RPCSX/llvm
1
0
Fork 0
mirror of https://github.com/RPCSX/llvm.git synced 2025-01-18 18:32:32 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

[SimplifyLibCalls] Turn memchr(const, C, const) into a bitfield check.

Browse Source 
strchr("123!", C) != nullptr is a common pattern to check if C is one
of 1, 2, 3 or !. If the largest element of the string is smaller than
the target's register size we can easily create a bitfield and just
do a simple test for set membership.

int foo(char C) { return strchr("123!", C) != nullptr; } now becomes

	cmpl	$64, %edi ## range check
	sbbb	%al, %al
	movabsq	$0xE000200000001, %rcx
	btq	%rdi, %rcx ## bit test
	sbbb	%cl, %cl
	andb	%al, %cl ## and the two conditions
	andb	$1, %cl
	movzbl	%cl, %eax ## returning an int
	ret

(imho the backend should expand this into a series of branches, but
that's a different story)

The code is currently limited to bit fields that fit in a register, so
usually 64 or 32 bits. Sadly, this misses anything using alpha chars
or {}. This could be fixed by just emitting a i128 bit field, but that
can generate really ugly code so we have to find a better way. To some
degree this is also recreating switch lowering logic, but we can't
simply emit a switch instruction and thus change the CFG within
instcombine.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232902 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2015-03-21 21:09:33 +00:00
parent 2bb644f469
commit fd48a80e14
4 changed files with 138 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
lib/Target/README.txt
View File

@ -1268,7 +1268,8 @@ int foo (void) {
..
else if (strchr ("<>", *intel_parser.op_string)
Those should be turned into a switch.
Those should be turned into a switch. SimplifyLibCalls only gets the second
case.
//===---------------------------------------------------------------------===//

54
lib/Transforms/Utils/SimplifyLibCalls.cpp
View File

@ -762,11 +762,9 @@ Value *LibCallSimplifier::optimizeMemChr(CallInst *CI, IRBuilder<> &B) {
if (LenC && LenC->isNullValue())
return Constant::getNullValue(CI->getType());
// Check if all arguments are constants. If so, we can constant fold.
// From now on we need at least constant length and string.
StringRef Str;
if (!CharC || !LenC ||
!getConstantStringInfo(SrcStr, Str, /*Offset=*/0,
/*TrimAtNul=*/false))
if (!LenC || !getConstantStringInfo(SrcStr, Str, 0, /*TrimAtNul=*/false))
return nullptr;
// Truncate the string to LenC. If Str is smaller than LenC we will still only
@ -774,6 +772,54 @@ Value *LibCallSimplifier::optimizeMemChr(CallInst *CI, IRBuilder<> &B) {
// return null if we don't find the char.
Str = Str.substr(0, LenC->getZExtValue());
// If the char is variable but the input str and length are not we can turn
// this memchr call into a simple bit field test. Of course this only works
// when the return value is only checked against null.
//
// It would be really nice to reuse switch lowering here but we can't change
// the CFG at this point.
//
// memchr("\r\n", C, 2) != nullptr -> (C & ((1 << '\r') | (1 << '\n'))) != 0
// after bounds check.
if (!CharC && !Str.empty() && isOnlyUsedInZeroEqualityComparison(CI)) {
unsigned char Max = *std::max_element(Str.begin(), Str.end());
// Make sure the bit field we're about to create fits in a register on the
// target.
// FIXME: On a 64 bit architecture this prevents us from using the
// interesting range of alpha ascii chars. We could do better by emitting
// two bitfields or shifting the range by 64 if no lower chars are used.
if (!DL.fitsInLegalInteger(Max + 1))
return nullptr;
// For the bit field use a power-of-2 type with at least 8 bits to avoid
// creating unnecessary illegal types.
unsigned char Width = NextPowerOf2(std::max((unsigned char)7, Max));
// Now build the bit field.
APInt Bitfield(Width, 0);
for (char C : Str)
Bitfield.setBit((unsigned char)C);
Value *BitfieldC = B.getInt(Bitfield);
// First check that the bit field access is within bounds.
Value *C = B.CreateZExtOrTrunc(CI->getArgOperand(1), BitfieldC->getType());
Value *Bounds = B.CreateICmp(ICmpInst::ICMP_ULT, C, B.getIntN(Width, Width),
"memchr.bounds");
// Create code that checks if the given bit is set in the field.
Value *Shl = B.CreateShl(B.getIntN(Width, 1ULL), C);
Value *Bits = B.CreateIsNotNull(B.CreateAnd(Shl, BitfieldC), "memchr.bits");
// Finally merge both checks and cast to pointer type. The inttoptr
// implicitly zexts the i1 to intptr type.
return B.CreateIntToPtr(B.CreateAnd(Bounds, Bits, "memchr"), CI->getType());
}
// Check if all arguments are constants. If so, we can constant fold.
if (!CharC)
return nullptr;
// Compute the offset.
size_t I = Str.find(CharC->getSExtValue() & 0xFF);
if (I == StringRef::npos) // Didn't find the char. memchr returns null.

69
test/Transforms/InstCombine/memchr.ll
View File

@ -1,11 +1,14 @@
; Test that the memchr library call simplifier works correctly.
; RUN: opt < %s -instcombine -S | FileCheck %s
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128-n8:16:32"
@hello = constant [14 x i8] c"hello world\5Cn\00"
@hellonull = constant [14 x i8] c"hello\00world\5Cn\00"
@null = constant [1 x i8] zeroinitializer
@newlines = constant [3 x i8] c"\0D\0A\00"
@single = constant [2 x i8] c"\1F\00"
@spaces = constant [4 x i8] c" \0D\0A\00"
@chp = global i8* zeroinitializer
declare i8* @memchr(i8*, i32, i32)
@ -119,3 +122,67 @@ define void @test9() {
store i8* %dst, i8** @chp
ret void
}
define void @test10() {
; CHECK-LABEL: @test10
; CHECK: store i8* null, i8** @chp, align 4
; CHECK-NOT: call i8* @memchr
; CHECK: ret void
%str = getelementptr [14 x i8], [14 x i8]* @hello, i32 0, i32 0
%dst = call i8* @memchr(i8* %str, i32 119, i32 6)
store i8* %dst, i8** @chp
ret void
}
; Check transformation memchr("\r\n", C, 2) != nullptr -> (C & 9216) != 0
define i1 @test11(i32 %C) {
; CHECK-LABEL: @test11
; CHECK-NEXT: [[TRUNC:%.*]] = trunc i32 %C to i16
; CHECK-NEXT: %memchr.bounds = icmp ult i16 [[TRUNC]], 16
; CHECK-NEXT: [[SHL:%.*]] = shl i16 1, [[TRUNC]]
; CHECK-NEXT: [[AND:%.*]] = and i16 [[SHL]], 9216
; CHECK-NEXT: %memchr.bits = icmp ne i16 [[AND]], 0
; CHECK-NEXT: %memchr = and i1 %memchr.bounds, %memchr.bits
; CHECK-NEXT: ret i1 %memchr
%dst = call i8* @memchr(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @newlines, i64 0, i64 0), i32 %C, i32 2)
%cmp = icmp ne i8* %dst, null
ret i1 %cmp
}
; No 64 bits here
define i1 @test12(i32 %C) {
; CHECK-LABEL: @test12
; CHECK-NEXT: %dst = call i8* @memchr(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @spaces, i32 0, i32 0), i32 %C, i32 3)
; CHECK-NEXT: %cmp = icmp ne i8* %dst, null
; CHECK-NEXT: ret i1 %cmp
%dst = call i8* @memchr(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @spaces, i64 0, i64 0), i32 %C, i32 3)
%cmp = icmp ne i8* %dst, null
ret i1 %cmp
}
define i1 @test13(i32 %C) {
; CHECK-LABEL: @test13
; CHECK-NEXT: %memchr.bounds = icmp ult i32 %C, 32
; CHECK-NEXT: [[SHL:%.*]] = shl i32 1, %C
; CHECK-NEXT: [[AND:%.*]] = and i32 [[SHL]], -2147483647
; CHECK-NEXT: %memchr.bits = icmp ne i32 [[AND]], 0
; CHECK-NEXT: %memchr = and i1 %memchr.bounds, %memchr.bits
; CHECK-NEXT: ret i1 %memchr
%dst = call i8* @memchr(i8* getelementptr inbounds ([2 x i8], [2 x i8]* @single, i64 0, i64 0), i32 %C, i32 2)
%cmp = icmp ne i8* %dst, null
ret i1 %cmp
}
define i1 @test14(i32 %C) {
; CHECK-LABEL: @test14
; CHECK-NEXT: icmp eq i32 %C, 31
; CHECK-NEXT: ret
%dst = call i8* @memchr(i8* getelementptr inbounds ([2 x i8], [2 x i8]* @single, i64 0, i64 0), i32 %C, i32 1)
%cmp = icmp ne i8* %dst, null
ret i1 %cmp
}

19
test/Transforms/InstCombine/strchr-1.ll
View File

@ -1,10 +1,11 @@
; Test that the strchr library call simplifier works correctly.
; RUN: opt < %s -instcombine -S | FileCheck %s
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128-n8:16:32"
@hello = constant [14 x i8] c"hello world\5Cn\00"
@null = constant [1 x i8] zeroinitializer
@newlines = constant [3 x i8] c"\0D\0A\00"
@chp = global i8* zeroinitializer
declare i8* @strchr(i8*, i32)
@ -76,3 +77,19 @@ define void @test_simplify6(i8* %str) {
store i8* %dst, i8** @chp
ret void
}
; Check transformation strchr("\r\n", C) != nullptr -> (C & 9217) != 0
define i1 @test_simplify7(i32 %C) {
; CHECK-LABEL: @test_simplify7
; CHECK-NEXT: [[TRUNC:%.*]] = trunc i32 %C to i16
; CHECK-NEXT: %memchr.bounds = icmp ult i16 [[TRUNC]], 16
; CHECK-NEXT: [[SHL:%.*]] = shl i16 1, [[TRUNC]]
; CHECK-NEXT: [[AND:%.*]] = and i16 [[SHL]], 9217
; CHECK-NEXT: %memchr.bits = icmp ne i16 [[AND]], 0
; CHECK-NEXT: %memchr1 = and i1 %memchr.bounds, %memchr.bits
; CHECK-NEXT: ret i1 %memchr1
%dst = call i8* @strchr(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @newlines, i64 0, i64 0), i32 %C)
%cmp = icmp ne i8* %dst, null
ret i1 %cmp
}