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[ExpandMemCmp] Properly expand bcmp to an equality pattern.

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Before that change, constant-size `bcmp` would miss an opportunity to generate
a more efficient equality pattern and would generate a -1/0-1 pattern
instead.

Differential Revision: https://reviews.llvm.org/D123849
This commit is contained in:
Clement Courbet 2022-04-15 11:11:26 +02:00
parent 866bd4df47
commit 46a13a0ef8
6 changed files with 23 additions and 39 deletions
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7
llvm/lib/CodeGen/ExpandMemCmp.cpp
View file

@ -740,7 +740,7 @@ Value *MemCmpExpansion::getMemCmpExpansion() {
static bool expandMemCmp(CallInst *CI, const TargetTransformInfo *TTI,
const TargetLowering *TLI, const DataLayout *DL,
ProfileSummaryInfo *PSI, BlockFrequencyInfo *BFI,
DomTreeUpdater *DTU) {
DomTreeUpdater *DTU, const bool IsBCmp) {
NumMemCmpCalls++;
// Early exit from expansion if -Oz.
@ -760,7 +760,8 @@ static bool expandMemCmp(CallInst *CI, const TargetTransformInfo *TTI,
}
// TTI call to check if target would like to expand memcmp. Also, get the
// available load sizes.
const bool IsUsedForZeroCmp = isOnlyUsedInZeroEqualityComparison(CI);
const bool IsUsedForZeroCmp =
IsBCmp || isOnlyUsedInZeroEqualityComparison(CI);
bool OptForSize = CI->getFunction()->hasOptSize() ||
llvm::shouldOptimizeForSize(CI->getParent(), PSI, BFI);
auto Options = TTI->enableMemCmpExpansion(OptForSize,
@ -864,7 +865,7 @@ bool ExpandMemCmpPass::runOnBlock(BasicBlock &BB, const TargetLibraryInfo *TLI,
LibFunc Func;
if (TLI->getLibFunc(*CI, Func) &&
(Func == LibFunc_memcmp || Func == LibFunc_bcmp) &&
expandMemCmp(CI, TTI, TL, &DL, PSI, BFI, DTU)) {
expandMemCmp(CI, TTI, TL, &DL, PSI, BFI, DTU, Func == LibFunc_bcmp)) {
return true;
}
}

11
llvm/test/CodeGen/X86/memcmp-optsize-x32.ll
View file

@ -569,15 +569,12 @@ define i1 @length64_eq_const(i8* %X) nounwind optsize {
define i32 @bcmp_length2(i8* %X, i8* %Y) nounwind optsize {
; X86-LABEL: bcmp_length2:
; X86: # %bb.0:
; X86-NEXT: movl {{[0-9]+}}(%esp), %eax
; X86-NEXT: movl {{[0-9]+}}(%esp), %ecx
; X86-NEXT: movzwl (%ecx), %ecx
; X86-NEXT: movl {{[0-9]+}}(%esp), %eax
; X86-NEXT: movzwl (%eax), %edx
; X86-NEXT: rolw $8, %cx
; X86-NEXT: rolw $8, %dx
; X86-NEXT: movzwl %cx, %eax
; X86-NEXT: movzwl %dx, %ecx
; X86-NEXT: subl %ecx, %eax
; X86-NEXT: xorl %eax, %eax
; X86-NEXT: cmpw (%ecx), %dx
; X86-NEXT: setne %al
; X86-NEXT: retl
%m = tail call i32 @bcmp(i8* %X, i8* %Y, i32 2) nounwind
ret i32 %m

11
llvm/test/CodeGen/X86/memcmp-optsize.ll
View file

@ -584,13 +584,10 @@ define i1 @length64_eq_const(i8* %X) nounwind optsize {
define i32 @bcmp_length2(i8* %X, i8* %Y) nounwind optsize {
; X64-LABEL: bcmp_length2:
; X64: # %bb.0:
; X64-NEXT: movzwl (%rdi), %eax
; X64-NEXT: movzwl (%rsi), %ecx
; X64-NEXT: rolw $8, %ax
; X64-NEXT: rolw $8, %cx
; X64-NEXT: movzwl %ax, %eax
; X64-NEXT: movzwl %cx, %ecx
; X64-NEXT: subl %ecx, %eax
; X64-NEXT: movzwl (%rdi), %ecx
; X64-NEXT: xorl %eax, %eax
; X64-NEXT: cmpw (%rsi), %cx
; X64-NEXT: setne %al
; X64-NEXT: retq
%m = tail call i32 @bcmp(i8* %X, i8* %Y, i64 2) nounwind
ret i32 %m

11
llvm/test/CodeGen/X86/memcmp-pgso-x32.ll
View file

@ -569,15 +569,12 @@ define i1 @length64_eq_const(i8* %X) nounwind !prof !14 {
define i32 @bcmp_length2(i8* %X, i8* %Y) nounwind !prof !14 {
; X86-LABEL: bcmp_length2:
; X86: # %bb.0:
; X86-NEXT: movl {{[0-9]+}}(%esp), %eax
; X86-NEXT: movl {{[0-9]+}}(%esp), %ecx
; X86-NEXT: movzwl (%ecx), %ecx
; X86-NEXT: movl {{[0-9]+}}(%esp), %eax
; X86-NEXT: movzwl (%eax), %edx
; X86-NEXT: rolw $8, %cx
; X86-NEXT: rolw $8, %dx
; X86-NEXT: movzwl %cx, %eax
; X86-NEXT: movzwl %dx, %ecx
; X86-NEXT: subl %ecx, %eax
; X86-NEXT: xorl %eax, %eax
; X86-NEXT: cmpw (%ecx), %dx
; X86-NEXT: setne %al
; X86-NEXT: retl
%m = tail call i32 @bcmp(i8* %X, i8* %Y, i32 2) nounwind
ret i32 %m

11
llvm/test/CodeGen/X86/memcmp-pgso.ll
View file

@ -584,13 +584,10 @@ define i1 @length64_eq_const(i8* %X) nounwind !prof !14 {
define i32 @bcmp_length2(i8* %X, i8* %Y) nounwind !prof !14 {
; X64-LABEL: bcmp_length2:
; X64: # %bb.0:
; X64-NEXT: movzwl (%rdi), %eax
; X64-NEXT: movzwl (%rsi), %ecx
; X64-NEXT: rolw $8, %ax
; X64-NEXT: rolw $8, %cx
; X64-NEXT: movzwl %ax, %eax
; X64-NEXT: movzwl %cx, %ecx
; X64-NEXT: subl %ecx, %eax
; X64-NEXT: movzwl (%rdi), %ecx
; X64-NEXT: xorl %eax, %eax
; X64-NEXT: cmpw (%rsi), %cx
; X64-NEXT: setne %al
; X64-NEXT: retq
%m = tail call i32 @bcmp(i8* %X, i8* %Y, i64 2) nounwind
ret i32 %m

11
llvm/test/Transforms/ExpandMemCmp/X86/bcmp.ll
View file

@ -9,14 +9,9 @@ define i32 @bcmp8(i8* nocapture readonly %x, i8* nocapture readonly %y) {
; X64-NEXT: [[TMP2:%.*]] = bitcast i8* [[Y:%.*]] to i64*
; X64-NEXT: [[TMP3:%.*]] = load i64, i64* [[TMP1]], align 1
; X64-NEXT: [[TMP4:%.*]] = load i64, i64* [[TMP2]], align 1
; X64-NEXT: [[TMP5:%.*]] = call i64 @llvm.bswap.i64(i64 [[TMP3]])
; X64-NEXT: [[TMP6:%.*]] = call i64 @llvm.bswap.i64(i64 [[TMP4]])
; X64-NEXT: [[TMP7:%.*]] = icmp ugt i64 [[TMP5]], [[TMP6]]
; X64-NEXT: [[TMP8:%.*]] = icmp ult i64 [[TMP5]], [[TMP6]]
; X64-NEXT: [[TMP9:%.*]] = zext i1 [[TMP7]] to i32
; X64-NEXT: [[TMP10:%.*]] = zext i1 [[TMP8]] to i32
; X64-NEXT: [[TMP11:%.*]] = sub i32 [[TMP9]], [[TMP10]]
; X64-NEXT: ret i32 [[TMP11]]
; X64-NEXT: [[TMP5:%.*]] = icmp ne i64 [[TMP3]], [[TMP4]]
; X64-NEXT: [[TMP6:%.*]] = zext i1 [[TMP5]] to i32
; X64-NEXT: ret i32 [[TMP6]]
;
%call = tail call i32 @bcmp(i8* %x, i8* %y, i64 8)
ret i32 %call