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c20995e070
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26708 91177308-0d34-0410-b5e6-96231b3b80d8
134 lines
3.6 KiB
Plaintext
134 lines
3.6 KiB
Plaintext
Target Independent Opportunities:
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===-------------------------------------------------------------------------===
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FreeBench/mason contains code like this:
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static p_type m0u(p_type p) {
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int m[]={0, 8, 1, 2, 16, 5, 13, 7, 14, 9, 3, 4, 11, 12, 15, 10, 17, 6};
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p_type pu;
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pu.a = m[p.a];
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pu.b = m[p.b];
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pu.c = m[p.c];
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return pu;
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}
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We currently compile this into a memcpy from a static array into 'm', then
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a bunch of loads from m. It would be better to avoid the memcpy and just do
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loads from the static array.
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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. :)
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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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//===---------------------------------------------------------------------===//
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DAG combine this into mul A, 8:
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int %test(int %A) {
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%B = mul int %A, 8 ;; shift
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%C = add int %B, 7 ;; dead, no demanded bits.
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%D = and int %C, -8 ;; dead once add is gone.
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ret int %D
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}
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This sort of thing occurs in the alloca lowering code and other places that
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are generating alignment of an already aligned value.
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//===---------------------------------------------------------------------===//
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Turn this into a signed shift right in instcombine:
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int f(unsigned x) {
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return x >> 31 ? -1 : 0;
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}
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25600
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http://gcc.gnu.org/ml/gcc-patches/2006-02/msg01492.html
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//===---------------------------------------------------------------------===//
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We should reassociate:
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int f(int a, int b){ return a * a + 2 * a * b + b * b; }
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into:
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int f(int a, int b) { return a * (a + 2 * b) + b * b; }
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to eliminate a multiply.
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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 is missing this:
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int test(int X, int Y) {
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return (X+X+Y+Y); // (X+Y) << 1;
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}
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it needs to turn the shifts into multiplies to get it.
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//===---------------------------------------------------------------------===//
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Reassociate should turn: X*X*X*X -> t=(X*X) (t*t) to eliminate a multiply.
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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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