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3e41106de4
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119925 91177308-0d34-0410-b5e6-96231b3b80d8
2022 lines
60 KiB
Plaintext
2022 lines
60 KiB
Plaintext
Target Independent Opportunities:
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//===---------------------------------------------------------------------===//
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We should recognize idioms for add-with-carry and turn it into the appropriate
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intrinsics. This example:
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unsigned add32carry(unsigned sum, unsigned x) {
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unsigned z = sum + x;
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if (sum + x < x)
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z++;
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return z;
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}
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Compiles to: clang t.c -S -o - -O3 -fomit-frame-pointer -m64 -mkernel
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_add32carry: ## @add32carry
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addl %esi, %edi
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cmpl %esi, %edi
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sbbl %eax, %eax
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andl $1, %eax
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addl %edi, %eax
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ret
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with clang, but to:
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_add32carry:
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leal (%rsi,%rdi), %eax
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cmpl %esi, %eax
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adcl $0, %eax
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ret
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with gcc.
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//===---------------------------------------------------------------------===//
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Dead argument elimination should be enhanced to handle cases when an argument is
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dead to an externally visible function. Though the argument can't be removed
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from the externally visible function, the caller doesn't need to pass it in.
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For example in this testcase:
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void foo(int X) __attribute__((noinline));
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void foo(int X) { sideeffect(); }
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void bar(int A) { foo(A+1); }
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We compile bar to:
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define void @bar(i32 %A) nounwind ssp {
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%0 = add nsw i32 %A, 1 ; <i32> [#uses=1]
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tail call void @foo(i32 %0) nounwind noinline ssp
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ret void
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}
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The add is dead, we could pass in 'i32 undef' instead. This occurs for C++
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templates etc, which usually have linkonce_odr/weak_odr linkage, not internal
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linkage.
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//===---------------------------------------------------------------------===//
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With the recent changes to make the implicit def/use set explicit in
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machineinstrs, we should change the target descriptions for 'call' instructions
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so that the .td files don't list all the call-clobbered registers as implicit
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defs. Instead, these should be added by the code generator (e.g. on the dag).
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This has a number of uses:
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1. PPC32/64 and X86 32/64 can avoid having multiple copies of call instructions
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for their different impdef sets.
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2. Targets with multiple calling convs (e.g. x86) which have different clobber
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sets don't need copies of call instructions.
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3. 'Interprocedural register allocation' can be done to reduce the clobber sets
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of calls.
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//===---------------------------------------------------------------------===//
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Make the PPC branch selector target independant
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//===---------------------------------------------------------------------===//
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Get the C front-end to expand hypot(x,y) -> llvm.sqrt(x*x+y*y) when errno and
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precision don't matter (ffastmath). Misc/mandel will like this. :) This isn't
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safe in general, even on darwin. See the libm implementation of hypot for
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examples (which special case when x/y are exactly zero to get signed zeros etc
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right).
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//===---------------------------------------------------------------------===//
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Solve this DAG isel folding deficiency:
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int X, Y;
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void fn1(void)
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{
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X = X | (Y << 3);
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}
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compiles to
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fn1:
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movl Y, %eax
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shll $3, %eax
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orl X, %eax
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movl %eax, X
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ret
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The problem is the store's chain operand is not the load X but rather
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a TokenFactor of the load X and load Y, which prevents the folding.
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There are two ways to fix this:
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1. The dag combiner can start using alias analysis to realize that y/x
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don't alias, making the store to X not dependent on the load from Y.
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2. The generated isel could be made smarter in the case it can't
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disambiguate the pointers.
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Number 1 is the preferred solution.
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This has been "fixed" by a TableGen hack. But that is a short term workaround
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which will be removed once the proper fix is made.
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//===---------------------------------------------------------------------===//
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On targets with expensive 64-bit multiply, we could LSR this:
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for (i = ...; ++i) {
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x = 1ULL << i;
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into:
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long long tmp = 1;
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for (i = ...; ++i, tmp+=tmp)
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x = tmp;
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This would be a win on ppc32, but not x86 or ppc64.
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//===---------------------------------------------------------------------===//
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Shrink: (setlt (loadi32 P), 0) -> (setlt (loadi8 Phi), 0)
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//===---------------------------------------------------------------------===//
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Reassociate should turn things like:
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int factorial(int X) {
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return X*X*X*X*X*X*X*X;
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}
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into llvm.powi calls, allowing the code generator to produce balanced
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multiplication trees.
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First, the intrinsic needs to be extended to support integers, and second the
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code generator needs to be enhanced to lower these to multiplication trees.
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//===---------------------------------------------------------------------===//
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Interesting? testcase for add/shift/mul reassoc:
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int bar(int x, int y) {
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return x*x*x+y+x*x*x*x*x*y*y*y*y;
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}
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int foo(int z, int n) {
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return bar(z, n) + bar(2*z, 2*n);
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}
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This is blocked on not handling X*X*X -> powi(X, 3) (see note above). The issue
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is that we end up getting t = 2*X s = t*t and don't turn this into 4*X*X,
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which is the same number of multiplies and is canonical, because the 2*X has
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multiple uses. Here's a simple example:
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define i32 @test15(i32 %X1) {
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%B = mul i32 %X1, 47 ; X1*47
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%C = mul i32 %B, %B
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ret i32 %C
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}
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//===---------------------------------------------------------------------===//
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Reassociate should handle the example in GCC PR16157:
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extern int a0, a1, a2, a3, a4; extern int b0, b1, b2, b3, b4;
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void f () { /* this can be optimized to four additions... */
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b4 = a4 + a3 + a2 + a1 + a0;
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b3 = a3 + a2 + a1 + a0;
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b2 = a2 + a1 + a0;
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b1 = a1 + a0;
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}
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This requires reassociating to forms of expressions that are already available,
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something that reassoc doesn't think about yet.
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//===---------------------------------------------------------------------===//
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This function: (derived from GCC PR19988)
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double foo(double x, double y) {
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return ((x + 0.1234 * y) * (x + -0.1234 * y));
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}
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compiles to:
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_foo:
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movapd %xmm1, %xmm2
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mulsd LCPI1_1(%rip), %xmm1
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mulsd LCPI1_0(%rip), %xmm2
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addsd %xmm0, %xmm1
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addsd %xmm0, %xmm2
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movapd %xmm1, %xmm0
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mulsd %xmm2, %xmm0
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ret
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Reassociate should be able to turn it into:
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double foo(double x, double y) {
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return ((x + 0.1234 * y) * (x - 0.1234 * y));
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}
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Which allows the multiply by constant to be CSE'd, producing:
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_foo:
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mulsd LCPI1_0(%rip), %xmm1
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movapd %xmm1, %xmm2
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addsd %xmm0, %xmm2
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subsd %xmm1, %xmm0
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mulsd %xmm2, %xmm0
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ret
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This doesn't need -ffast-math support at all. This is particularly bad because
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the llvm-gcc frontend is canonicalizing the later into the former, but clang
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doesn't have this problem.
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//===---------------------------------------------------------------------===//
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These two functions should generate the same code on big-endian systems:
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int g(int *j,int *l) { return memcmp(j,l,4); }
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int h(int *j, int *l) { return *j - *l; }
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this could be done in SelectionDAGISel.cpp, along with other special cases,
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for 1,2,4,8 bytes.
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//===---------------------------------------------------------------------===//
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It would be nice to revert this patch:
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http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20060213/031986.html
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And teach the dag combiner enough to simplify the code expanded before
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legalize. It seems plausible that this knowledge would let it simplify other
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stuff too.
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//===---------------------------------------------------------------------===//
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For vector types, TargetData.cpp::getTypeInfo() returns alignment that is equal
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to the type size. It works but can be overly conservative as the alignment of
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specific vector types are target dependent.
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//===---------------------------------------------------------------------===//
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We should produce an unaligned load from code like this:
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v4sf example(float *P) {
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return (v4sf){P[0], P[1], P[2], P[3] };
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}
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//===---------------------------------------------------------------------===//
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Add support for conditional increments, and other related patterns. Instead
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of:
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movl 136(%esp), %eax
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cmpl $0, %eax
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je LBB16_2 #cond_next
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LBB16_1: #cond_true
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incl _foo
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LBB16_2: #cond_next
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emit:
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movl _foo, %eax
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cmpl $1, %edi
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sbbl $-1, %eax
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movl %eax, _foo
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//===---------------------------------------------------------------------===//
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Combine: a = sin(x), b = cos(x) into a,b = sincos(x).
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Expand these to calls of sin/cos and stores:
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double sincos(double x, double *sin, double *cos);
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float sincosf(float x, float *sin, float *cos);
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long double sincosl(long double x, long double *sin, long double *cos);
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Doing so could allow SROA of the destination pointers. See also:
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17687
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This is now easily doable with MRVs. We could even make an intrinsic for this
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if anyone cared enough about sincos.
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//===---------------------------------------------------------------------===//
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quantum_sigma_x in 462.libquantum contains the following loop:
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for(i=0; i<reg->size; i++)
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{
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/* Flip the target bit of each basis state */
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reg->node[i].state ^= ((MAX_UNSIGNED) 1 << target);
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}
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Where MAX_UNSIGNED/state is a 64-bit int. On a 32-bit platform it would be just
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so cool to turn it into something like:
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long long Res = ((MAX_UNSIGNED) 1 << target);
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if (target < 32) {
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for(i=0; i<reg->size; i++)
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reg->node[i].state ^= Res & 0xFFFFFFFFULL;
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} else {
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for(i=0; i<reg->size; i++)
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reg->node[i].state ^= Res & 0xFFFFFFFF00000000ULL
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}
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... which would only do one 32-bit XOR per loop iteration instead of two.
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It would also be nice to recognize the reg->size doesn't alias reg->node[i], but
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this requires TBAA.
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//===---------------------------------------------------------------------===//
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This isn't recognized as bswap by instcombine (yes, it really is bswap):
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unsigned long reverse(unsigned v) {
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unsigned t;
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t = v ^ ((v << 16) | (v >> 16));
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t &= ~0xff0000;
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v = (v << 24) | (v >> 8);
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return v ^ (t >> 8);
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}
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Neither is this (very standard idiom):
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int f(int n)
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{
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return (((n) << 24) | (((n) & 0xff00) << 8)
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| (((n) >> 8) & 0xff00) | ((n) >> 24));
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}
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//===---------------------------------------------------------------------===//
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[LOOP RECOGNITION]
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These idioms should be recognized as popcount (see PR1488):
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unsigned countbits_slow(unsigned v) {
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unsigned c;
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for (c = 0; v; v >>= 1)
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c += v & 1;
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return c;
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}
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unsigned countbits_fast(unsigned v){
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unsigned c;
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for (c = 0; v; c++)
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v &= v - 1; // clear the least significant bit set
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return c;
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}
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BITBOARD = unsigned long long
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int PopCnt(register BITBOARD a) {
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register int c=0;
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while(a) {
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c++;
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a &= a - 1;
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}
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return c;
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}
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unsigned int popcount(unsigned int input) {
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unsigned int count = 0;
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for (unsigned int i = 0; i < 4 * 8; i++)
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count += (input >> i) & i;
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return count;
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}
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This is a form of idiom recognition for loops, the same thing that could be
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useful for recognizing memset/memcpy.
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//===---------------------------------------------------------------------===//
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These should turn into single 16-bit (unaligned?) loads on little/big endian
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processors.
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unsigned short read_16_le(const unsigned char *adr) {
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return adr[0] | (adr[1] << 8);
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}
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unsigned short read_16_be(const unsigned char *adr) {
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return (adr[0] << 8) | adr[1];
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}
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//===---------------------------------------------------------------------===//
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-instcombine should handle this transform:
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icmp pred (sdiv X / C1 ), C2
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when X, C1, and C2 are unsigned. Similarly for udiv and signed operands.
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Currently InstCombine avoids this transform but will do it when the signs of
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the operands and the sign of the divide match. See the FIXME in
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InstructionCombining.cpp in the visitSetCondInst method after the switch case
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for Instruction::UDiv (around line 4447) for more details.
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The SingleSource/Benchmarks/Shootout-C++/hash and hash2 tests have examples of
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this construct.
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//===---------------------------------------------------------------------===//
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[LOOP RECOGNITION]
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viterbi speeds up *significantly* if the various "history" related copy loops
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are turned into memcpy calls at the source level. We need a "loops to memcpy"
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pass.
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//===---------------------------------------------------------------------===//
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[LOOP OPTIMIZATION]
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SingleSource/Benchmarks/Misc/dt.c shows several interesting optimization
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opportunities in its double_array_divs_variable function: it needs loop
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interchange, memory promotion (which LICM already does), vectorization and
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variable trip count loop unrolling (since it has a constant trip count). ICC
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apparently produces this very nice code with -ffast-math:
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..B1.70: # Preds ..B1.70 ..B1.69
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mulpd %xmm0, %xmm1 #108.2
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mulpd %xmm0, %xmm1 #108.2
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mulpd %xmm0, %xmm1 #108.2
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mulpd %xmm0, %xmm1 #108.2
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addl $8, %edx #
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cmpl $131072, %edx #108.2
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jb ..B1.70 # Prob 99% #108.2
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It would be better to count down to zero, but this is a lot better than what we
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do.
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//===---------------------------------------------------------------------===//
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Consider:
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typedef unsigned U32;
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typedef unsigned long long U64;
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int test (U32 *inst, U64 *regs) {
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U64 effective_addr2;
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U32 temp = *inst;
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int r1 = (temp >> 20) & 0xf;
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int b2 = (temp >> 16) & 0xf;
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effective_addr2 = temp & 0xfff;
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if (b2) effective_addr2 += regs[b2];
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b2 = (temp >> 12) & 0xf;
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if (b2) effective_addr2 += regs[b2];
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effective_addr2 &= regs[4];
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if ((effective_addr2 & 3) == 0)
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return 1;
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return 0;
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}
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Note that only the low 2 bits of effective_addr2 are used. On 32-bit systems,
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we don't eliminate the computation of the top half of effective_addr2 because
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we don't have whole-function selection dags. On x86, this means we use one
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extra register for the function when effective_addr2 is declared as U64 than
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when it is declared U32.
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PHI Slicing could be extended to do this.
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//===---------------------------------------------------------------------===//
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LSR should know what GPR types a target has from TargetData. This code:
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volatile short X, Y; // globals
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void foo(int N) {
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int i;
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for (i = 0; i < N; i++) { X = i; Y = i*4; }
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}
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produces two near identical IV's (after promotion) on PPC/ARM:
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LBB1_2:
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ldr r3, LCPI1_0
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ldr r3, [r3]
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strh r2, [r3]
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ldr r3, LCPI1_1
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ldr r3, [r3]
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strh r1, [r3]
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add r1, r1, #4
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add r2, r2, #1 <- [0,+,1]
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sub r0, r0, #1 <- [0,-,1]
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cmp r0, #0
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bne LBB1_2
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LSR should reuse the "+" IV for the exit test.
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//===---------------------------------------------------------------------===//
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Tail call elim should be more aggressive, checking to see if the call is
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followed by an uncond branch to an exit block.
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; This testcase is due to tail-duplication not wanting to copy the return
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; instruction into the terminating blocks because there was other code
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; optimized out of the function after the taildup happened.
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; RUN: llvm-as < %s | opt -tailcallelim | llvm-dis | not grep call
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define i32 @t4(i32 %a) {
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entry:
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%tmp.1 = and i32 %a, 1 ; <i32> [#uses=1]
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%tmp.2 = icmp ne i32 %tmp.1, 0 ; <i1> [#uses=1]
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br i1 %tmp.2, label %then.0, label %else.0
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then.0: ; preds = %entry
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%tmp.5 = add i32 %a, -1 ; <i32> [#uses=1]
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%tmp.3 = call i32 @t4( i32 %tmp.5 ) ; <i32> [#uses=1]
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br label %return
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else.0: ; preds = %entry
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%tmp.7 = icmp ne i32 %a, 0 ; <i1> [#uses=1]
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br i1 %tmp.7, label %then.1, label %return
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then.1: ; preds = %else.0
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%tmp.11 = add i32 %a, -2 ; <i32> [#uses=1]
|
|
%tmp.9 = call i32 @t4( i32 %tmp.11 ) ; <i32> [#uses=1]
|
|
br label %return
|
|
|
|
return: ; preds = %then.1, %else.0, %then.0
|
|
%result.0 = phi i32 [ 0, %else.0 ], [ %tmp.3, %then.0 ],
|
|
[ %tmp.9, %then.1 ]
|
|
ret i32 %result.0
|
|
}
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Tail recursion elimination should handle:
|
|
|
|
int pow2m1(int n) {
|
|
if (n == 0)
|
|
return 0;
|
|
return 2 * pow2m1 (n - 1) + 1;
|
|
}
|
|
|
|
Also, multiplies can be turned into SHL's, so they should be handled as if
|
|
they were associative. "return foo() << 1" can be tail recursion eliminated.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Argument promotion should promote arguments for recursive functions, like
|
|
this:
|
|
|
|
; RUN: llvm-as < %s | opt -argpromotion | llvm-dis | grep x.val
|
|
|
|
define internal i32 @foo(i32* %x) {
|
|
entry:
|
|
%tmp = load i32* %x ; <i32> [#uses=0]
|
|
%tmp.foo = call i32 @foo( i32* %x ) ; <i32> [#uses=1]
|
|
ret i32 %tmp.foo
|
|
}
|
|
|
|
define i32 @bar(i32* %x) {
|
|
entry:
|
|
%tmp3 = call i32 @foo( i32* %x ) ; <i32> [#uses=1]
|
|
ret i32 %tmp3
|
|
}
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We should investigate an instruction sinking pass. Consider this silly
|
|
example in pic mode:
|
|
|
|
#include <assert.h>
|
|
void foo(int x) {
|
|
assert(x);
|
|
//...
|
|
}
|
|
|
|
we compile this to:
|
|
_foo:
|
|
subl $28, %esp
|
|
call "L1$pb"
|
|
"L1$pb":
|
|
popl %eax
|
|
cmpl $0, 32(%esp)
|
|
je LBB1_2 # cond_true
|
|
LBB1_1: # return
|
|
# ...
|
|
addl $28, %esp
|
|
ret
|
|
LBB1_2: # cond_true
|
|
...
|
|
|
|
The PIC base computation (call+popl) is only used on one path through the
|
|
code, but is currently always computed in the entry block. It would be
|
|
better to sink the picbase computation down into the block for the
|
|
assertion, as it is the only one that uses it. This happens for a lot of
|
|
code with early outs.
|
|
|
|
Another example is loads of arguments, which are usually emitted into the
|
|
entry block on targets like x86. If not used in all paths through a
|
|
function, they should be sunk into the ones that do.
|
|
|
|
In this case, whole-function-isel would also handle this.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Investigate lowering of sparse switch statements into perfect hash tables:
|
|
http://burtleburtle.net/bob/hash/perfect.html
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We should turn things like "load+fabs+store" and "load+fneg+store" into the
|
|
corresponding integer operations. On a yonah, this loop:
|
|
|
|
double a[256];
|
|
void foo() {
|
|
int i, b;
|
|
for (b = 0; b < 10000000; b++)
|
|
for (i = 0; i < 256; i++)
|
|
a[i] = -a[i];
|
|
}
|
|
|
|
is twice as slow as this loop:
|
|
|
|
long long a[256];
|
|
void foo() {
|
|
int i, b;
|
|
for (b = 0; b < 10000000; b++)
|
|
for (i = 0; i < 256; i++)
|
|
a[i] ^= (1ULL << 63);
|
|
}
|
|
|
|
and I suspect other processors are similar. On X86 in particular this is a
|
|
big win because doing this with integers allows the use of read/modify/write
|
|
instructions.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
DAG Combiner should try to combine small loads into larger loads when
|
|
profitable. For example, we compile this C++ example:
|
|
|
|
struct THotKey { short Key; bool Control; bool Shift; bool Alt; };
|
|
extern THotKey m_HotKey;
|
|
THotKey GetHotKey () { return m_HotKey; }
|
|
|
|
into (-O3 -fno-exceptions -static -fomit-frame-pointer):
|
|
|
|
__Z9GetHotKeyv:
|
|
pushl %esi
|
|
movl 8(%esp), %eax
|
|
movb _m_HotKey+3, %cl
|
|
movb _m_HotKey+4, %dl
|
|
movb _m_HotKey+2, %ch
|
|
movw _m_HotKey, %si
|
|
movw %si, (%eax)
|
|
movb %ch, 2(%eax)
|
|
movb %cl, 3(%eax)
|
|
movb %dl, 4(%eax)
|
|
popl %esi
|
|
ret $4
|
|
|
|
GCC produces:
|
|
|
|
__Z9GetHotKeyv:
|
|
movl _m_HotKey, %edx
|
|
movl 4(%esp), %eax
|
|
movl %edx, (%eax)
|
|
movzwl _m_HotKey+4, %edx
|
|
movw %dx, 4(%eax)
|
|
ret $4
|
|
|
|
The LLVM IR contains the needed alignment info, so we should be able to
|
|
merge the loads and stores into 4-byte loads:
|
|
|
|
%struct.THotKey = type { i16, i8, i8, i8 }
|
|
define void @_Z9GetHotKeyv(%struct.THotKey* sret %agg.result) nounwind {
|
|
...
|
|
%tmp2 = load i16* getelementptr (@m_HotKey, i32 0, i32 0), align 8
|
|
%tmp5 = load i8* getelementptr (@m_HotKey, i32 0, i32 1), align 2
|
|
%tmp8 = load i8* getelementptr (@m_HotKey, i32 0, i32 2), align 1
|
|
%tmp11 = load i8* getelementptr (@m_HotKey, i32 0, i32 3), align 2
|
|
|
|
Alternatively, we should use a small amount of base-offset alias analysis
|
|
to make it so the scheduler doesn't need to hold all the loads in regs at
|
|
once.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We should add an FRINT node to the DAG to model targets that have legal
|
|
implementations of ceil/floor/rint.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Consider:
|
|
|
|
int test() {
|
|
long long input[8] = {1,1,1,1,1,1,1,1};
|
|
foo(input);
|
|
}
|
|
|
|
We currently compile this into a memcpy from a global array since the
|
|
initializer is fairly large and not memset'able. This is good, but the memcpy
|
|
gets lowered to load/stores in the code generator. This is also ok, except
|
|
that the codegen lowering for memcpy doesn't handle the case when the source
|
|
is a constant global. This gives us atrocious code like this:
|
|
|
|
call "L1$pb"
|
|
"L1$pb":
|
|
popl %eax
|
|
movl _C.0.1444-"L1$pb"+32(%eax), %ecx
|
|
movl %ecx, 40(%esp)
|
|
movl _C.0.1444-"L1$pb"+20(%eax), %ecx
|
|
movl %ecx, 28(%esp)
|
|
movl _C.0.1444-"L1$pb"+36(%eax), %ecx
|
|
movl %ecx, 44(%esp)
|
|
movl _C.0.1444-"L1$pb"+44(%eax), %ecx
|
|
movl %ecx, 52(%esp)
|
|
movl _C.0.1444-"L1$pb"+40(%eax), %ecx
|
|
movl %ecx, 48(%esp)
|
|
movl _C.0.1444-"L1$pb"+12(%eax), %ecx
|
|
movl %ecx, 20(%esp)
|
|
movl _C.0.1444-"L1$pb"+4(%eax), %ecx
|
|
...
|
|
|
|
instead of:
|
|
movl $1, 16(%esp)
|
|
movl $0, 20(%esp)
|
|
movl $1, 24(%esp)
|
|
movl $0, 28(%esp)
|
|
movl $1, 32(%esp)
|
|
movl $0, 36(%esp)
|
|
...
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
http://llvm.org/PR717:
|
|
|
|
The following code should compile into "ret int undef". Instead, LLVM
|
|
produces "ret int 0":
|
|
|
|
int f() {
|
|
int x = 4;
|
|
int y;
|
|
if (x == 3) y = 0;
|
|
return y;
|
|
}
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
The loop unroller should partially unroll loops (instead of peeling them)
|
|
when code growth isn't too bad and when an unroll count allows simplification
|
|
of some code within the loop. One trivial example is:
|
|
|
|
#include <stdio.h>
|
|
int main() {
|
|
int nRet = 17;
|
|
int nLoop;
|
|
for ( nLoop = 0; nLoop < 1000; nLoop++ ) {
|
|
if ( nLoop & 1 )
|
|
nRet += 2;
|
|
else
|
|
nRet -= 1;
|
|
}
|
|
return nRet;
|
|
}
|
|
|
|
Unrolling by 2 would eliminate the '&1' in both copies, leading to a net
|
|
reduction in code size. The resultant code would then also be suitable for
|
|
exit value computation.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We miss a bunch of rotate opportunities on various targets, including ppc, x86,
|
|
etc. On X86, we miss a bunch of 'rotate by variable' cases because the rotate
|
|
matching code in dag combine doesn't look through truncates aggressively
|
|
enough. Here are some testcases reduces from GCC PR17886:
|
|
|
|
unsigned long long f(unsigned long long x, int y) {
|
|
return (x << y) | (x >> 64-y);
|
|
}
|
|
unsigned f2(unsigned x, int y){
|
|
return (x << y) | (x >> 32-y);
|
|
}
|
|
unsigned long long f3(unsigned long long x){
|
|
int y = 9;
|
|
return (x << y) | (x >> 64-y);
|
|
}
|
|
unsigned f4(unsigned x){
|
|
int y = 10;
|
|
return (x << y) | (x >> 32-y);
|
|
}
|
|
unsigned long long f5(unsigned long long x, unsigned long long y) {
|
|
return (x << 8) | ((y >> 48) & 0xffull);
|
|
}
|
|
unsigned long long f6(unsigned long long x, unsigned long long y, int z) {
|
|
switch(z) {
|
|
case 1:
|
|
return (x << 8) | ((y >> 48) & 0xffull);
|
|
case 2:
|
|
return (x << 16) | ((y >> 40) & 0xffffull);
|
|
case 3:
|
|
return (x << 24) | ((y >> 32) & 0xffffffull);
|
|
case 4:
|
|
return (x << 32) | ((y >> 24) & 0xffffffffull);
|
|
default:
|
|
return (x << 40) | ((y >> 16) & 0xffffffffffull);
|
|
}
|
|
}
|
|
|
|
On X86-64, we only handle f2/f3/f4 right. On x86-32, a few of these
|
|
generate truly horrible code, instead of using shld and friends. On
|
|
ARM, we end up with calls to L___lshrdi3/L___ashldi3 in f, which is
|
|
badness. PPC64 misses f, f5 and f6. CellSPU aborts in isel.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We do a number of simplifications in simplify libcalls to strength reduce
|
|
standard library functions, but we don't currently merge them together. For
|
|
example, it is useful to merge memcpy(a,b,strlen(b)) -> strcpy. This can only
|
|
be done safely if "b" isn't modified between the strlen and memcpy of course.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We compile this program: (from GCC PR11680)
|
|
http://gcc.gnu.org/bugzilla/attachment.cgi?id=4487
|
|
|
|
Into code that runs the same speed in fast/slow modes, but both modes run 2x
|
|
slower than when compile with GCC (either 4.0 or 4.2):
|
|
|
|
$ llvm-g++ perf.cpp -O3 -fno-exceptions
|
|
$ time ./a.out fast
|
|
1.821u 0.003s 0:01.82 100.0% 0+0k 0+0io 0pf+0w
|
|
|
|
$ g++ perf.cpp -O3 -fno-exceptions
|
|
$ time ./a.out fast
|
|
0.821u 0.001s 0:00.82 100.0% 0+0k 0+0io 0pf+0w
|
|
|
|
It looks like we are making the same inlining decisions, so this may be raw
|
|
codegen badness or something else (haven't investigated).
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We miss some instcombines for stuff like this:
|
|
void bar (void);
|
|
void foo (unsigned int a) {
|
|
/* This one is equivalent to a >= (3 << 2). */
|
|
if ((a >> 2) >= 3)
|
|
bar ();
|
|
}
|
|
|
|
A few other related ones are in GCC PR14753.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Divisibility by constant can be simplified (according to GCC PR12849) from
|
|
being a mulhi to being a mul lo (cheaper). Testcase:
|
|
|
|
void bar(unsigned n) {
|
|
if (n % 3 == 0)
|
|
true();
|
|
}
|
|
|
|
This is equivalent to the following, where 2863311531 is the multiplicative
|
|
inverse of 3, and 1431655766 is ((2^32)-1)/3+1:
|
|
void bar(unsigned n) {
|
|
if (n * 2863311531U < 1431655766U)
|
|
true();
|
|
}
|
|
|
|
The same transformation can work with an even modulo with the addition of a
|
|
rotate: rotate the result of the multiply to the right by the number of bits
|
|
which need to be zero for the condition to be true, and shrink the compare RHS
|
|
by the same amount. Unless the target supports rotates, though, that
|
|
transformation probably isn't worthwhile.
|
|
|
|
The transformation can also easily be made to work with non-zero equality
|
|
comparisons: just transform, for example, "n % 3 == 1" to "(n-1) % 3 == 0".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Better mod/ref analysis for scanf would allow us to eliminate the vtable and a
|
|
bunch of other stuff from this example (see PR1604):
|
|
|
|
#include <cstdio>
|
|
struct test {
|
|
int val;
|
|
virtual ~test() {}
|
|
};
|
|
|
|
int main() {
|
|
test t;
|
|
std::scanf("%d", &t.val);
|
|
std::printf("%d\n", t.val);
|
|
}
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
These functions perform the same computation, but produce different assembly.
|
|
|
|
define i8 @select(i8 %x) readnone nounwind {
|
|
%A = icmp ult i8 %x, 250
|
|
%B = select i1 %A, i8 0, i8 1
|
|
ret i8 %B
|
|
}
|
|
|
|
define i8 @addshr(i8 %x) readnone nounwind {
|
|
%A = zext i8 %x to i9
|
|
%B = add i9 %A, 6 ;; 256 - 250 == 6
|
|
%C = lshr i9 %B, 8
|
|
%D = trunc i9 %C to i8
|
|
ret i8 %D
|
|
}
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
From gcc bug 24696:
|
|
int
|
|
f (unsigned long a, unsigned long b, unsigned long c)
|
|
{
|
|
return ((a & (c - 1)) != 0) || ((b & (c - 1)) != 0);
|
|
}
|
|
int
|
|
f (unsigned long a, unsigned long b, unsigned long c)
|
|
{
|
|
return ((a & (c - 1)) != 0) | ((b & (c - 1)) != 0);
|
|
}
|
|
Both should combine to ((a|b) & (c-1)) != 0. Currently not optimized with
|
|
"clang -emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
From GCC Bug 20192:
|
|
#define PMD_MASK (~((1UL << 23) - 1))
|
|
void clear_pmd_range(unsigned long start, unsigned long end)
|
|
{
|
|
if (!(start & ~PMD_MASK) && !(end & ~PMD_MASK))
|
|
f();
|
|
}
|
|
The expression should optimize to something like
|
|
"!((start|end)&~PMD_MASK). Currently not optimized with "clang
|
|
-emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
void a(int variable)
|
|
{
|
|
if (variable == 4 || variable == 6)
|
|
bar();
|
|
}
|
|
This should optimize to "if ((variable | 2) == 6)". Currently not
|
|
optimized with "clang -emit-llvm-bc | opt -std-compile-opts | llc".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
unsigned int f(unsigned int i, unsigned int n) {++i; if (i == n) ++i; return
|
|
i;}
|
|
unsigned int f2(unsigned int i, unsigned int n) {++i; i += i == n; return i;}
|
|
These should combine to the same thing. Currently, the first function
|
|
produces better code on X86.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
From GCC Bug 15784:
|
|
#define abs(x) x>0?x:-x
|
|
int f(int x, int y)
|
|
{
|
|
return (abs(x)) >= 0;
|
|
}
|
|
This should optimize to x == INT_MIN. (With -fwrapv.) Currently not
|
|
optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
From GCC Bug 14753:
|
|
void
|
|
rotate_cst (unsigned int a)
|
|
{
|
|
a = (a << 10) | (a >> 22);
|
|
if (a == 123)
|
|
bar ();
|
|
}
|
|
void
|
|
minus_cst (unsigned int a)
|
|
{
|
|
unsigned int tem;
|
|
|
|
tem = 20 - a;
|
|
if (tem == 5)
|
|
bar ();
|
|
}
|
|
void
|
|
mask_gt (unsigned int a)
|
|
{
|
|
/* This is equivalent to a > 15. */
|
|
if ((a & ~7) > 8)
|
|
bar ();
|
|
}
|
|
void
|
|
rshift_gt (unsigned int a)
|
|
{
|
|
/* This is equivalent to a > 23. */
|
|
if ((a >> 2) > 5)
|
|
bar ();
|
|
}
|
|
All should simplify to a single comparison. All of these are
|
|
currently not optimized with "clang -emit-llvm-bc | opt
|
|
-std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
From GCC Bug 32605:
|
|
int c(int* x) {return (char*)x+2 == (char*)x;}
|
|
Should combine to 0. Currently not optimized with "clang
|
|
-emit-llvm-bc | opt -std-compile-opts" (although llc can optimize it).
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
int a(unsigned b) {return ((b << 31) | (b << 30)) >> 31;}
|
|
Should be combined to "((b >> 1) | b) & 1". Currently not optimized
|
|
with "clang -emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
unsigned a(unsigned x, unsigned y) { return x | (y & 1) | (y & 2);}
|
|
Should combine to "x | (y & 3)". Currently not optimized with "clang
|
|
-emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
int a(int a, int b, int c) {return (~a & c) | ((c|a) & b);}
|
|
Should fold to "(~a & c) | (a & b)". Currently not optimized with
|
|
"clang -emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
int a(int a,int b) {return (~(a|b))|a;}
|
|
Should fold to "a|~b". Currently not optimized with "clang
|
|
-emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
int a(int a, int b) {return (a&&b) || (a&&!b);}
|
|
Should fold to "a". Currently not optimized with "clang -emit-llvm-bc
|
|
| opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
int a(int a, int b, int c) {return (a&&b) || (!a&&c);}
|
|
Should fold to "a ? b : c", or at least something sane. Currently not
|
|
optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
int a(int a, int b, int c) {return (a&&b) || (a&&c) || (a&&b&&c);}
|
|
Should fold to a && (b || c). Currently not optimized with "clang
|
|
-emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
int a(int x) {return x | ((x & 8) ^ 8);}
|
|
Should combine to x | 8. Currently not optimized with "clang
|
|
-emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
int a(int x) {return x ^ ((x & 8) ^ 8);}
|
|
Should also combine to x | 8. Currently not optimized with "clang
|
|
-emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
int a(int x) {return (x & 8) == 0 ? -1 : -9;}
|
|
Should combine to (x | -9) ^ 8. Currently not optimized with "clang
|
|
-emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
int a(int x) {return (x & 8) == 0 ? -9 : -1;}
|
|
Should combine to x | -9. Currently not optimized with "clang
|
|
-emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
int a(int x) {return ((x | -9) ^ 8) & x;}
|
|
Should combine to x & -9. Currently not optimized with "clang
|
|
-emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
unsigned a(unsigned a) {return a * 0x11111111 >> 28 & 1;}
|
|
Should combine to "a * 0x88888888 >> 31". Currently not optimized
|
|
with "clang -emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
unsigned a(char* x) {if ((*x & 32) == 0) return b();}
|
|
There's an unnecessary zext in the generated code with "clang
|
|
-emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
unsigned a(unsigned long long x) {return 40 * (x >> 1);}
|
|
Should combine to "20 * (((unsigned)x) & -2)". Currently not
|
|
optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
This was noticed in the entryblock for grokdeclarator in 403.gcc:
|
|
|
|
%tmp = icmp eq i32 %decl_context, 4
|
|
%decl_context_addr.0 = select i1 %tmp, i32 3, i32 %decl_context
|
|
%tmp1 = icmp eq i32 %decl_context_addr.0, 1
|
|
%decl_context_addr.1 = select i1 %tmp1, i32 0, i32 %decl_context_addr.0
|
|
|
|
tmp1 should be simplified to something like:
|
|
(!tmp || decl_context == 1)
|
|
|
|
This allows recursive simplifications, tmp1 is used all over the place in
|
|
the function, e.g. by:
|
|
|
|
%tmp23 = icmp eq i32 %decl_context_addr.1, 0 ; <i1> [#uses=1]
|
|
%tmp24 = xor i1 %tmp1, true ; <i1> [#uses=1]
|
|
%or.cond8 = and i1 %tmp23, %tmp24 ; <i1> [#uses=1]
|
|
|
|
later.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
[STORE SINKING]
|
|
|
|
Store sinking: This code:
|
|
|
|
void f (int n, int *cond, int *res) {
|
|
int i;
|
|
*res = 0;
|
|
for (i = 0; i < n; i++)
|
|
if (*cond)
|
|
*res ^= 234; /* (*) */
|
|
}
|
|
|
|
On this function GVN hoists the fully redundant value of *res, but nothing
|
|
moves the store out. This gives us this code:
|
|
|
|
bb: ; preds = %bb2, %entry
|
|
%.rle = phi i32 [ 0, %entry ], [ %.rle6, %bb2 ]
|
|
%i.05 = phi i32 [ 0, %entry ], [ %indvar.next, %bb2 ]
|
|
%1 = load i32* %cond, align 4
|
|
%2 = icmp eq i32 %1, 0
|
|
br i1 %2, label %bb2, label %bb1
|
|
|
|
bb1: ; preds = %bb
|
|
%3 = xor i32 %.rle, 234
|
|
store i32 %3, i32* %res, align 4
|
|
br label %bb2
|
|
|
|
bb2: ; preds = %bb, %bb1
|
|
%.rle6 = phi i32 [ %3, %bb1 ], [ %.rle, %bb ]
|
|
%indvar.next = add i32 %i.05, 1
|
|
%exitcond = icmp eq i32 %indvar.next, %n
|
|
br i1 %exitcond, label %return, label %bb
|
|
|
|
DSE should sink partially dead stores to get the store out of the loop.
|
|
|
|
Here's another partial dead case:
|
|
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12395
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Scalar PRE hoists the mul in the common block up to the else:
|
|
|
|
int test (int a, int b, int c, int g) {
|
|
int d, e;
|
|
if (a)
|
|
d = b * c;
|
|
else
|
|
d = b - c;
|
|
e = b * c + g;
|
|
return d + e;
|
|
}
|
|
|
|
It would be better to do the mul once to reduce codesize above the if.
|
|
This is GCC PR38204.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
[STORE SINKING]
|
|
|
|
GCC PR37810 is an interesting case where we should sink load/store reload
|
|
into the if block and outside the loop, so we don't reload/store it on the
|
|
non-call path.
|
|
|
|
for () {
|
|
*P += 1;
|
|
if ()
|
|
call();
|
|
else
|
|
...
|
|
->
|
|
tmp = *P
|
|
for () {
|
|
tmp += 1;
|
|
if () {
|
|
*P = tmp;
|
|
call();
|
|
tmp = *P;
|
|
} else ...
|
|
}
|
|
*P = tmp;
|
|
|
|
We now hoist the reload after the call (Transforms/GVN/lpre-call-wrap.ll), but
|
|
we don't sink the store. We need partially dead store sinking.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
[LOAD PRE CRIT EDGE SPLITTING]
|
|
|
|
GCC PR37166: Sinking of loads prevents SROA'ing the "g" struct on the stack
|
|
leading to excess stack traffic. This could be handled by GVN with some crazy
|
|
symbolic phi translation. The code we get looks like (g is on the stack):
|
|
|
|
bb2: ; preds = %bb1
|
|
..
|
|
%9 = getelementptr %struct.f* %g, i32 0, i32 0
|
|
store i32 %8, i32* %9, align bel %bb3
|
|
|
|
bb3: ; preds = %bb1, %bb2, %bb
|
|
%c_addr.0 = phi %struct.f* [ %g, %bb2 ], [ %c, %bb ], [ %c, %bb1 ]
|
|
%b_addr.0 = phi %struct.f* [ %b, %bb2 ], [ %g, %bb ], [ %b, %bb1 ]
|
|
%10 = getelementptr %struct.f* %c_addr.0, i32 0, i32 0
|
|
%11 = load i32* %10, align 4
|
|
|
|
%11 is partially redundant, an in BB2 it should have the value %8.
|
|
|
|
GCC PR33344 and PR35287 are similar cases.
|
|
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
[LOAD PRE]
|
|
|
|
There are many load PRE testcases in testsuite/gcc.dg/tree-ssa/loadpre* in the
|
|
GCC testsuite, ones we don't get yet are (checked through loadpre25):
|
|
|
|
[CRIT EDGE BREAKING]
|
|
loadpre3.c predcom-4.c
|
|
|
|
[PRE OF READONLY CALL]
|
|
loadpre5.c
|
|
|
|
[TURN SELECT INTO BRANCH]
|
|
loadpre14.c loadpre15.c
|
|
|
|
actually a conditional increment: loadpre18.c loadpre19.c
|
|
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
[SCALAR PRE]
|
|
There are many PRE testcases in testsuite/gcc.dg/tree-ssa/ssa-pre-*.c in the
|
|
GCC testsuite.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
There are some interesting cases in testsuite/gcc.dg/tree-ssa/pred-comm* in the
|
|
GCC testsuite. For example, we get the first example in predcom-1.c, but
|
|
miss the second one:
|
|
|
|
unsigned fib[1000];
|
|
unsigned avg[1000];
|
|
|
|
__attribute__ ((noinline))
|
|
void count_averages(int n) {
|
|
int i;
|
|
for (i = 1; i < n; i++)
|
|
avg[i] = (((unsigned long) fib[i - 1] + fib[i] + fib[i + 1]) / 3) & 0xffff;
|
|
}
|
|
|
|
which compiles into two loads instead of one in the loop.
|
|
|
|
predcom-2.c is the same as predcom-1.c
|
|
|
|
predcom-3.c is very similar but needs loads feeding each other instead of
|
|
store->load.
|
|
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
[ALIAS ANALYSIS]
|
|
|
|
Type based alias analysis:
|
|
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14705
|
|
|
|
We should do better analysis of posix_memalign. At the least it should
|
|
no-capture its pointer argument, at best, we should know that the out-value
|
|
result doesn't point to anything (like malloc). One example of this is in
|
|
SingleSource/Benchmarks/Misc/dt.c
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
A/B get pinned to the stack because we turn an if/then into a select instead
|
|
of PRE'ing the load/store. This may be fixable in instcombine:
|
|
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37892
|
|
|
|
struct X { int i; };
|
|
int foo (int x) {
|
|
struct X a;
|
|
struct X b;
|
|
struct X *p;
|
|
a.i = 1;
|
|
b.i = 2;
|
|
if (x)
|
|
p = &a;
|
|
else
|
|
p = &b;
|
|
return p->i;
|
|
}
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Interesting missed case because of control flow flattening (should be 2 loads):
|
|
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26629
|
|
With: llvm-gcc t2.c -S -o - -O0 -emit-llvm | llvm-as |
|
|
opt -mem2reg -gvn -instcombine | llvm-dis
|
|
we miss it because we need 1) CRIT EDGE 2) MULTIPLE DIFFERENT
|
|
VALS PRODUCED BY ONE BLOCK OVER DIFFERENT PATHS
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19633
|
|
We could eliminate the branch condition here, loading from null is undefined:
|
|
|
|
struct S { int w, x, y, z; };
|
|
struct T { int r; struct S s; };
|
|
void bar (struct S, int);
|
|
void foo (int a, struct T b)
|
|
{
|
|
struct S *c = 0;
|
|
if (a)
|
|
c = &b.s;
|
|
bar (*c, a);
|
|
}
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
simplifylibcalls should do several optimizations for strspn/strcspn:
|
|
|
|
strcspn(x, "a") -> inlined loop for up to 3 letters (similarly for strspn):
|
|
|
|
size_t __strcspn_c3 (__const char *__s, int __reject1, int __reject2,
|
|
int __reject3) {
|
|
register size_t __result = 0;
|
|
while (__s[__result] != '\0' && __s[__result] != __reject1 &&
|
|
__s[__result] != __reject2 && __s[__result] != __reject3)
|
|
++__result;
|
|
return __result;
|
|
}
|
|
|
|
This should turn into a switch on the character. See PR3253 for some notes on
|
|
codegen.
|
|
|
|
456.hmmer apparently uses strcspn and strspn a lot. 471.omnetpp uses strspn.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
"gas" uses this idiom:
|
|
else if (strchr ("+-/*%|&^:[]()~", *intel_parser.op_string))
|
|
..
|
|
else if (strchr ("<>", *intel_parser.op_string)
|
|
|
|
Those should be turned into a switch.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
252.eon contains this interesting code:
|
|
|
|
%3072 = getelementptr [100 x i8]* %tempString, i32 0, i32 0
|
|
%3073 = call i8* @strcpy(i8* %3072, i8* %3071) nounwind
|
|
%strlen = call i32 @strlen(i8* %3072) ; uses = 1
|
|
%endptr = getelementptr [100 x i8]* %tempString, i32 0, i32 %strlen
|
|
call void @llvm.memcpy.i32(i8* %endptr,
|
|
i8* getelementptr ([5 x i8]* @"\01LC42", i32 0, i32 0), i32 5, i32 1)
|
|
%3074 = call i32 @strlen(i8* %endptr) nounwind readonly
|
|
|
|
This is interesting for a couple reasons. First, in this:
|
|
|
|
%3073 = call i8* @strcpy(i8* %3072, i8* %3071) nounwind
|
|
%strlen = call i32 @strlen(i8* %3072)
|
|
|
|
The strlen could be replaced with: %strlen = sub %3072, %3073, because the
|
|
strcpy call returns a pointer to the end of the string. Based on that, the
|
|
endptr GEP just becomes equal to 3073, which eliminates a strlen call and GEP.
|
|
|
|
Second, the memcpy+strlen strlen can be replaced with:
|
|
|
|
%3074 = call i32 @strlen([5 x i8]* @"\01LC42") nounwind readonly
|
|
|
|
Because the destination was just copied into the specified memory buffer. This,
|
|
in turn, can be constant folded to "4".
|
|
|
|
In other code, it contains:
|
|
|
|
%endptr6978 = bitcast i8* %endptr69 to i32*
|
|
store i32 7107374, i32* %endptr6978, align 1
|
|
%3167 = call i32 @strlen(i8* %endptr69) nounwind readonly
|
|
|
|
Which could also be constant folded. Whatever is producing this should probably
|
|
be fixed to leave this as a memcpy from a string.
|
|
|
|
Further, eon also has an interesting partially redundant strlen call:
|
|
|
|
bb8: ; preds = %_ZN18eonImageCalculatorC1Ev.exit
|
|
%682 = getelementptr i8** %argv, i32 6 ; <i8**> [#uses=2]
|
|
%683 = load i8** %682, align 4 ; <i8*> [#uses=4]
|
|
%684 = load i8* %683, align 1 ; <i8> [#uses=1]
|
|
%685 = icmp eq i8 %684, 0 ; <i1> [#uses=1]
|
|
br i1 %685, label %bb10, label %bb9
|
|
|
|
bb9: ; preds = %bb8
|
|
%686 = call i32 @strlen(i8* %683) nounwind readonly
|
|
%687 = icmp ugt i32 %686, 254 ; <i1> [#uses=1]
|
|
br i1 %687, label %bb10, label %bb11
|
|
|
|
bb10: ; preds = %bb9, %bb8
|
|
%688 = call i32 @strlen(i8* %683) nounwind readonly
|
|
|
|
This could be eliminated by doing the strlen once in bb8, saving code size and
|
|
improving perf on the bb8->9->10 path.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
I see an interesting fully redundant call to strlen left in 186.crafty:InputMove
|
|
which looks like:
|
|
%movetext11 = getelementptr [128 x i8]* %movetext, i32 0, i32 0
|
|
|
|
|
|
bb62: ; preds = %bb55, %bb53
|
|
%promote.0 = phi i32 [ %169, %bb55 ], [ 0, %bb53 ]
|
|
%171 = call i32 @strlen(i8* %movetext11) nounwind readonly align 1
|
|
%172 = add i32 %171, -1 ; <i32> [#uses=1]
|
|
%173 = getelementptr [128 x i8]* %movetext, i32 0, i32 %172
|
|
|
|
... no stores ...
|
|
br i1 %or.cond, label %bb65, label %bb72
|
|
|
|
bb65: ; preds = %bb62
|
|
store i8 0, i8* %173, align 1
|
|
br label %bb72
|
|
|
|
bb72: ; preds = %bb65, %bb62
|
|
%trank.1 = phi i32 [ %176, %bb65 ], [ -1, %bb62 ]
|
|
%177 = call i32 @strlen(i8* %movetext11) nounwind readonly align 1
|
|
|
|
Note that on the bb62->bb72 path, that the %177 strlen call is partially
|
|
redundant with the %171 call. At worst, we could shove the %177 strlen call
|
|
up into the bb65 block moving it out of the bb62->bb72 path. However, note
|
|
that bb65 stores to the string, zeroing out the last byte. This means that on
|
|
that path the value of %177 is actually just %171-1. A sub is cheaper than a
|
|
strlen!
|
|
|
|
This pattern repeats several times, basically doing:
|
|
|
|
A = strlen(P);
|
|
P[A-1] = 0;
|
|
B = strlen(P);
|
|
where it is "obvious" that B = A-1.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
186.crafty also contains this code:
|
|
|
|
%1906 = call i32 @strlen(i8* getelementptr ([32 x i8]* @pgn_event, i32 0,i32 0))
|
|
%1907 = getelementptr [32 x i8]* @pgn_event, i32 0, i32 %1906
|
|
%1908 = call i8* @strcpy(i8* %1907, i8* %1905) nounwind align 1
|
|
%1909 = call i32 @strlen(i8* getelementptr ([32 x i8]* @pgn_event, i32 0,i32 0))
|
|
%1910 = getelementptr [32 x i8]* @pgn_event, i32 0, i32 %1909
|
|
|
|
The last strlen is computable as 1908-@pgn_event, which means 1910=1908.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
186.crafty has this interesting pattern with the "out.4543" variable:
|
|
|
|
call void @llvm.memcpy.i32(
|
|
i8* getelementptr ([10 x i8]* @out.4543, i32 0, i32 0),
|
|
i8* getelementptr ([7 x i8]* @"\01LC28700", i32 0, i32 0), i32 7, i32 1)
|
|
%101 = call@printf(i8* ... @out.4543, i32 0, i32 0)) nounwind
|
|
|
|
It is basically doing:
|
|
|
|
memcpy(globalarray, "string");
|
|
printf(..., globalarray);
|
|
|
|
Anyway, by knowing that printf just reads the memory and forward substituting
|
|
the string directly into the printf, this eliminates reads from globalarray.
|
|
Since this pattern occurs frequently in crafty (due to the "DisplayTime" and
|
|
other similar functions) there are many stores to "out". Once all the printfs
|
|
stop using "out", all that is left is the memcpy's into it. This should allow
|
|
globalopt to remove the "stored only" global.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
This code:
|
|
|
|
define inreg i32 @foo(i8* inreg %p) nounwind {
|
|
%tmp0 = load i8* %p
|
|
%tmp1 = ashr i8 %tmp0, 5
|
|
%tmp2 = sext i8 %tmp1 to i32
|
|
ret i32 %tmp2
|
|
}
|
|
|
|
could be dagcombine'd to a sign-extending load with a shift.
|
|
For example, on x86 this currently gets this:
|
|
|
|
movb (%eax), %al
|
|
sarb $5, %al
|
|
movsbl %al, %eax
|
|
|
|
while it could get this:
|
|
|
|
movsbl (%eax), %eax
|
|
sarl $5, %eax
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
GCC PR31029:
|
|
|
|
int test(int x) { return 1-x == x; } // --> return false
|
|
int test2(int x) { return 2-x == x; } // --> return x == 1 ?
|
|
|
|
Always foldable for odd constants, what is the rule for even?
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
PR 3381: GEP to field of size 0 inside a struct could be turned into GEP
|
|
for next field in struct (which is at same address).
|
|
|
|
For example: store of float into { {{}}, float } could be turned into a store to
|
|
the float directly.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
The arg promotion pass should make use of nocapture to make its alias analysis
|
|
stuff much more precise.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
The following functions should be optimized to use a select instead of a
|
|
branch (from gcc PR40072):
|
|
|
|
char char_int(int m) {if(m>7) return 0; return m;}
|
|
int int_char(char m) {if(m>7) return 0; return m;}
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
int func(int a, int b) { if (a & 0x80) b |= 0x80; else b &= ~0x80; return b; }
|
|
|
|
Generates this:
|
|
|
|
define i32 @func(i32 %a, i32 %b) nounwind readnone ssp {
|
|
entry:
|
|
%0 = and i32 %a, 128 ; <i32> [#uses=1]
|
|
%1 = icmp eq i32 %0, 0 ; <i1> [#uses=1]
|
|
%2 = or i32 %b, 128 ; <i32> [#uses=1]
|
|
%3 = and i32 %b, -129 ; <i32> [#uses=1]
|
|
%b_addr.0 = select i1 %1, i32 %3, i32 %2 ; <i32> [#uses=1]
|
|
ret i32 %b_addr.0
|
|
}
|
|
|
|
However, it's functionally equivalent to:
|
|
|
|
b = (b & ~0x80) | (a & 0x80);
|
|
|
|
Which generates this:
|
|
|
|
define i32 @func(i32 %a, i32 %b) nounwind readnone ssp {
|
|
entry:
|
|
%0 = and i32 %b, -129 ; <i32> [#uses=1]
|
|
%1 = and i32 %a, 128 ; <i32> [#uses=1]
|
|
%2 = or i32 %0, %1 ; <i32> [#uses=1]
|
|
ret i32 %2
|
|
}
|
|
|
|
This can be generalized for other forms:
|
|
|
|
b = (b & ~0x80) | (a & 0x40) << 1;
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
These two functions produce different code. They shouldn't:
|
|
|
|
#include <stdint.h>
|
|
|
|
uint8_t p1(uint8_t b, uint8_t a) {
|
|
b = (b & ~0xc0) | (a & 0xc0);
|
|
return (b);
|
|
}
|
|
|
|
uint8_t p2(uint8_t b, uint8_t a) {
|
|
b = (b & ~0x40) | (a & 0x40);
|
|
b = (b & ~0x80) | (a & 0x80);
|
|
return (b);
|
|
}
|
|
|
|
define zeroext i8 @p1(i8 zeroext %b, i8 zeroext %a) nounwind readnone ssp {
|
|
entry:
|
|
%0 = and i8 %b, 63 ; <i8> [#uses=1]
|
|
%1 = and i8 %a, -64 ; <i8> [#uses=1]
|
|
%2 = or i8 %1, %0 ; <i8> [#uses=1]
|
|
ret i8 %2
|
|
}
|
|
|
|
define zeroext i8 @p2(i8 zeroext %b, i8 zeroext %a) nounwind readnone ssp {
|
|
entry:
|
|
%0 = and i8 %b, 63 ; <i8> [#uses=1]
|
|
%.masked = and i8 %a, 64 ; <i8> [#uses=1]
|
|
%1 = and i8 %a, -128 ; <i8> [#uses=1]
|
|
%2 = or i8 %1, %0 ; <i8> [#uses=1]
|
|
%3 = or i8 %2, %.masked ; <i8> [#uses=1]
|
|
ret i8 %3
|
|
}
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
IPSCCP does not currently propagate argument dependent constants through
|
|
functions where it does not not all of the callers. This includes functions
|
|
with normal external linkage as well as templates, C99 inline functions etc.
|
|
Specifically, it does nothing to:
|
|
|
|
define i32 @test(i32 %x, i32 %y, i32 %z) nounwind {
|
|
entry:
|
|
%0 = add nsw i32 %y, %z
|
|
%1 = mul i32 %0, %x
|
|
%2 = mul i32 %y, %z
|
|
%3 = add nsw i32 %1, %2
|
|
ret i32 %3
|
|
}
|
|
|
|
define i32 @test2() nounwind {
|
|
entry:
|
|
%0 = call i32 @test(i32 1, i32 2, i32 4) nounwind
|
|
ret i32 %0
|
|
}
|
|
|
|
It would be interesting extend IPSCCP to be able to handle simple cases like
|
|
this, where all of the arguments to a call are constant. Because IPSCCP runs
|
|
before inlining, trivial templates and inline functions are not yet inlined.
|
|
The results for a function + set of constant arguments should be memoized in a
|
|
map.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
The libcall constant folding stuff should be moved out of SimplifyLibcalls into
|
|
libanalysis' constantfolding logic. This would allow IPSCCP to be able to
|
|
handle simple things like this:
|
|
|
|
static int foo(const char *X) { return strlen(X); }
|
|
int bar() { return foo("abcd"); }
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
InstCombine should use SimplifyDemandedBits to remove the or instruction:
|
|
|
|
define i1 @test(i8 %x, i8 %y) {
|
|
%A = or i8 %x, 1
|
|
%B = icmp ugt i8 %A, 3
|
|
ret i1 %B
|
|
}
|
|
|
|
Currently instcombine calls SimplifyDemandedBits with either all bits or just
|
|
the sign bit, if the comparison is obviously a sign test. In this case, we only
|
|
need all but the bottom two bits from %A, and if we gave that mask to SDB it
|
|
would delete the or instruction for us.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
functionattrs doesn't know much about memcpy/memset. This function should be
|
|
marked readnone rather than readonly, since it only twiddles local memory, but
|
|
functionattrs doesn't handle memset/memcpy/memmove aggressively:
|
|
|
|
struct X { int *p; int *q; };
|
|
int foo() {
|
|
int i = 0, j = 1;
|
|
struct X x, y;
|
|
int **p;
|
|
y.p = &i;
|
|
x.q = &j;
|
|
p = __builtin_memcpy (&x, &y, sizeof (int *));
|
|
return **p;
|
|
}
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Missed instcombine transformation:
|
|
define i1 @a(i32 %x) nounwind readnone {
|
|
entry:
|
|
%cmp = icmp eq i32 %x, 30
|
|
%sub = add i32 %x, -30
|
|
%cmp2 = icmp ugt i32 %sub, 9
|
|
%or = or i1 %cmp, %cmp2
|
|
ret i1 %or
|
|
}
|
|
This should be optimized to a single compare. Testcase derived from gcc.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Missed instcombine or reassociate transformation:
|
|
int a(int a, int b) { return (a==12)&(b>47)&(b<58); }
|
|
|
|
The sgt and slt should be combined into a single comparison. Testcase derived
|
|
from gcc.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Missed instcombine transformation:
|
|
define i32 @a(i32 %x) nounwind readnone {
|
|
entry:
|
|
%rem = srem i32 %x, 32
|
|
%shl = shl i32 1, %rem
|
|
ret i32 %shl
|
|
}
|
|
|
|
The srem can be transformed to an and because if x is negative, the shift is
|
|
undefined. Here's a more general case that occurs on 64-bit targets:
|
|
|
|
%382 = srem i32 %tmp14.i, 64 ; [#uses=1]
|
|
%383 = zext i32 %382 to i64 ; [#uses=1]
|
|
%384 = shl i64 %381, %383 ; [#uses=1]
|
|
%385 = icmp slt i32 %tmp14.i, 64 ; [#uses=1]
|
|
|
|
Testcase derived from 403.gcc.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
This is a range comparison on a divided result (from 403.gcc):
|
|
|
|
%1337 = sdiv i32 %1336, 8 ; [#uses=1]
|
|
%.off.i208 = add i32 %1336, 7 ; [#uses=1]
|
|
%1338 = icmp ult i32 %.off.i208, 15 ; [#uses=1]
|
|
|
|
We already catch this (removing the sdiv) if there isn't an add, we should
|
|
handle the 'add' as well. This is a common idiom with it's builtin_alloca code.
|
|
C testcase:
|
|
|
|
int a(int x) { return (unsigned)(x/16+7) < 15; }
|
|
|
|
Another similar case involves truncations on 64-bit targets:
|
|
|
|
%361 = sdiv i64 %.046, 8 ; [#uses=1]
|
|
%362 = trunc i64 %361 to i32 ; [#uses=2]
|
|
...
|
|
%367 = icmp eq i32 %362, 0 ; [#uses=1]
|
|
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Missed instcombine/dagcombine transformation:
|
|
define i32 @a(i32 %x, i32 %y) nounwind readnone {
|
|
entry:
|
|
%mul = mul i32 %y, -8
|
|
%sub = sub i32 %x, %mul
|
|
ret i32 %sub
|
|
}
|
|
|
|
Should compile to something like x+y*8, but currently compiles to an
|
|
inefficient result. Testcase derived from gcc. C testcase:
|
|
|
|
int a(int x, int y) { return y-x*-8; }
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Missed instcombine/dagcombine transformation:
|
|
define void @lshift_lt(i8 zeroext %a) nounwind {
|
|
entry:
|
|
%conv = zext i8 %a to i32
|
|
%shl = shl i32 %conv, 3
|
|
%cmp = icmp ult i32 %shl, 33
|
|
br i1 %cmp, label %if.then, label %if.end
|
|
|
|
if.then:
|
|
tail call void @bar() nounwind
|
|
ret void
|
|
|
|
if.end:
|
|
ret void
|
|
}
|
|
declare void @bar() nounwind
|
|
|
|
The shift should be eliminated. Testcase derived from gcc.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
These compile into different code, one gets recognized as a switch and the
|
|
other doesn't due to phase ordering issues (PR6212):
|
|
|
|
int test1(int mainType, int subType) {
|
|
if (mainType == 7)
|
|
subType = 4;
|
|
else if (mainType == 9)
|
|
subType = 6;
|
|
else if (mainType == 11)
|
|
subType = 9;
|
|
return subType;
|
|
}
|
|
|
|
int test2(int mainType, int subType) {
|
|
if (mainType == 7)
|
|
subType = 4;
|
|
if (mainType == 9)
|
|
subType = 6;
|
|
if (mainType == 11)
|
|
subType = 9;
|
|
return subType;
|
|
}
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
The following test case (from PR6576):
|
|
|
|
define i32 @mul(i32 %a, i32 %b) nounwind readnone {
|
|
entry:
|
|
%cond1 = icmp eq i32 %b, 0 ; <i1> [#uses=1]
|
|
br i1 %cond1, label %exit, label %bb.nph
|
|
bb.nph: ; preds = %entry
|
|
%tmp = mul i32 %b, %a ; <i32> [#uses=1]
|
|
ret i32 %tmp
|
|
exit: ; preds = %entry
|
|
ret i32 0
|
|
}
|
|
|
|
could be reduced to:
|
|
|
|
define i32 @mul(i32 %a, i32 %b) nounwind readnone {
|
|
entry:
|
|
%tmp = mul i32 %b, %a
|
|
ret i32 %tmp
|
|
}
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We should use DSE + llvm.lifetime.end to delete dead vtable pointer updates.
|
|
See GCC PR34949
|
|
|
|
Another interesting case is that something related could be used for variables
|
|
that go const after their ctor has finished. In these cases, globalopt (which
|
|
can statically run the constructor) could mark the global const (so it gets put
|
|
in the readonly section). A testcase would be:
|
|
|
|
#include <complex>
|
|
using namespace std;
|
|
const complex<char> should_be_in_rodata (42,-42);
|
|
complex<char> should_be_in_data (42,-42);
|
|
complex<char> should_be_in_bss;
|
|
|
|
Where we currently evaluate the ctors but the globals don't become const because
|
|
the optimizer doesn't know they "become const" after the ctor is done. See
|
|
GCC PR4131 for more examples.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
In this code:
|
|
|
|
long foo(long x) {
|
|
return x > 1 ? x : 1;
|
|
}
|
|
|
|
LLVM emits a comparison with 1 instead of 0. 0 would be equivalent
|
|
and cheaper on most targets.
|
|
|
|
LLVM prefers comparisons with zero over non-zero in general, but in this
|
|
case it choses instead to keep the max operation obvious.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Take the following testcase on x86-64 (similar testcases exist for all targets
|
|
with addc/adde):
|
|
|
|
define void @a(i64* nocapture %s, i64* nocapture %t, i64 %a, i64 %b,
|
|
i64 %c) nounwind {
|
|
entry:
|
|
%0 = zext i64 %a to i128 ; <i128> [#uses=1]
|
|
%1 = zext i64 %b to i128 ; <i128> [#uses=1]
|
|
%2 = add i128 %1, %0 ; <i128> [#uses=2]
|
|
%3 = zext i64 %c to i128 ; <i128> [#uses=1]
|
|
%4 = shl i128 %3, 64 ; <i128> [#uses=1]
|
|
%5 = add i128 %4, %2 ; <i128> [#uses=1]
|
|
%6 = lshr i128 %5, 64 ; <i128> [#uses=1]
|
|
%7 = trunc i128 %6 to i64 ; <i64> [#uses=1]
|
|
store i64 %7, i64* %s, align 8
|
|
%8 = trunc i128 %2 to i64 ; <i64> [#uses=1]
|
|
store i64 %8, i64* %t, align 8
|
|
ret void
|
|
}
|
|
|
|
Generated code:
|
|
addq %rcx, %rdx
|
|
movl $0, %eax
|
|
adcq $0, %rax
|
|
addq %r8, %rax
|
|
movq %rax, (%rdi)
|
|
movq %rdx, (%rsi)
|
|
ret
|
|
|
|
Expected code:
|
|
addq %rcx, %rdx
|
|
adcq $0, %r8
|
|
movq %r8, (%rdi)
|
|
movq %rdx, (%rsi)
|
|
ret
|
|
|
|
The generated SelectionDAG has an ADD of an ADDE, where both operands of the
|
|
ADDE are zero. Replacing one of the operands of the ADDE with the other operand
|
|
of the ADD, and replacing the ADD with the ADDE, should give the desired result.
|
|
|
|
(That said, we are doing a lot better than gcc on this testcase. :) )
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Switch lowering generates less than ideal code for the following switch:
|
|
define void @a(i32 %x) nounwind {
|
|
entry:
|
|
switch i32 %x, label %if.end [
|
|
i32 0, label %if.then
|
|
i32 1, label %if.then
|
|
i32 2, label %if.then
|
|
i32 3, label %if.then
|
|
i32 5, label %if.then
|
|
]
|
|
if.then:
|
|
tail call void @foo() nounwind
|
|
ret void
|
|
if.end:
|
|
ret void
|
|
}
|
|
declare void @foo()
|
|
|
|
Generated code on x86-64 (other platforms give similar results):
|
|
a:
|
|
cmpl $5, %edi
|
|
ja .LBB0_2
|
|
movl %edi, %eax
|
|
movl $47, %ecx
|
|
btq %rax, %rcx
|
|
jb .LBB0_3
|
|
.LBB0_2:
|
|
ret
|
|
.LBB0_3:
|
|
jmp foo # TAILCALL
|
|
|
|
The movl+movl+btq+jb could be simplified to a cmpl+jne.
|
|
|
|
Or, if we wanted to be really clever, we could simplify the whole thing to
|
|
something like the following, which eliminates a branch:
|
|
xorl $1, %edi
|
|
cmpl $4, %edi
|
|
ja .LBB0_2
|
|
ret
|
|
.LBB0_2:
|
|
jmp foo # TAILCALL
|
|
//===---------------------------------------------------------------------===//
|
|
Given a branch where the two target blocks are identical ("ret i32 %b" in
|
|
both), simplifycfg will simplify them away. But not so for a switch statement:
|
|
|
|
define i32 @f(i32 %a, i32 %b) nounwind readnone {
|
|
entry:
|
|
switch i32 %a, label %bb3 [
|
|
i32 4, label %bb
|
|
i32 6, label %bb
|
|
]
|
|
|
|
bb: ; preds = %entry, %entry
|
|
ret i32 %b
|
|
|
|
bb3: ; preds = %entry
|
|
ret i32 %b
|
|
}
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
clang -O3 fails to devirtualize this virtual inheritance case: (GCC PR45875)
|
|
Looks related to PR3100
|
|
|
|
struct c1 {};
|
|
struct c10 : c1{
|
|
virtual void foo ();
|
|
};
|
|
struct c11 : c10, c1{
|
|
virtual void f6 ();
|
|
};
|
|
struct c28 : virtual c11{
|
|
void f6 ();
|
|
};
|
|
void check_c28 () {
|
|
c28 obj;
|
|
c11 *ptr = &obj;
|
|
ptr->f6 ();
|
|
}
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We compile this:
|
|
|
|
int foo(int a) { return (a & (~15)) / 16; }
|
|
|
|
Into:
|
|
|
|
define i32 @foo(i32 %a) nounwind readnone ssp {
|
|
entry:
|
|
%and = and i32 %a, -16
|
|
%div = sdiv i32 %and, 16
|
|
ret i32 %div
|
|
}
|
|
|
|
but this code (X & -A)/A is X >> log2(A) when A is a power of 2, so this case
|
|
should be instcombined into just "a >> 4".
|
|
|
|
We do get this at the codegen level, so something knows about it, but
|
|
instcombine should catch it earlier:
|
|
|
|
_foo: ## @foo
|
|
## BB#0: ## %entry
|
|
movl %edi, %eax
|
|
sarl $4, %eax
|
|
ret
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|