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[AArch64] Report icmp as free if it can be folded into ands #143286

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Jun 17, 2025
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[AArch64] Report icmp as free if it can be folded into ands #143286

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Pre-commit tests (NFC)
AZero13 Jun 16, 2025
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[AArch64] Report icmp as free if it can be folded into ands
AZero13 Jun 16, 2025
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25 changes: 18 additions & 7 deletions llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4353,15 +4353,26 @@ InstructionCost AArch64TTIImpl::getCmpSelInstrCost(
}
}

// Treat the icmp in icmp(and, 0) as free, as we can make use of ands.
// FIXME: This can apply to more conditions and add/sub if it can be shown to
// be profitable.
// Treat the icmp in icmp(and, 0) or icmp(and, -1/1) when it can be folded to
// icmp(and, 0) as free, as we can make use of ands, but only if the
// comparison is not unsigned.
if (ValTy->isIntegerTy() && ISD == ISD::SETCC && I &&
ICmpInst::isEquality(VecPred) &&
!CmpInst::isUnsigned(VecPred) &&
TLI->isTypeLegal(TLI->getValueType(DL, ValTy)) &&
match(I->getOperand(1), m_Zero()) &&
match(I->getOperand(0), m_And(m_Value(), m_Value())))
return 0;
match(I->getOperand(0), m_And(m_Value(), m_Value()))) {
if (match(I->getOperand(1), m_Zero()))
return 0;

// x >= 1 / x < 1 -> x > 0 / x <= 0
if (match(I->getOperand(1), m_One()) &&
(VecPred == CmpInst::ICMP_SLT || VecPred == CmpInst::ICMP_SGE))
return 0;

// x <= -1 / x > -1 -> x > 0 / x <= 0
if (match(I->getOperand(1), m_AllOnes()) &&
(VecPred == CmpInst::ICMP_SLE || VecPred == CmpInst::ICMP_SGT))
return 0;
}

// The base case handles scalable vectors fine for now, since it treats the
// cost as 1 * legalization cost.
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21 changes: 20 additions & 1 deletion llvm/test/Analysis/CostModel/AArch64/cmp.ll
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Expand Up @@ -53,6 +53,14 @@ define void @andcmp() {
; CHECK-NEXT: Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: %c32 = icmp eq i32 %a32, 0
; CHECK-NEXT: Cost Model: Found costs of 1 for: %a64 = and i64 undef, undef
; CHECK-NEXT: Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: %c64 = icmp ne i64 %a64, 0
; CHECK-NEXT: Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: %c32ge = icmp sge i32 %a32, 1
; CHECK-NEXT: Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: %c32le = icmp slt i32 %a32, 1
; CHECK-NEXT: Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: %c32leneg = icmp sle i32 %a32, -1
; CHECK-NEXT: Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: %c32gtneg = icmp sgt i32 %a32, -1
; CHECK-NEXT: Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: %c64ge = icmp sge i64 %a64, 1
; CHECK-NEXT: Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: %c64le = icmp slt i64 %a64, 1
; CHECK-NEXT: Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: %c64leneg = icmp sle i64 %a64, -1
; CHECK-NEXT: Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: %c64gtneg = icmp sgt i64 %a64, -1
; CHECK-NEXT: Cost Model: Found costs of RThru:2 CodeSize:1 Lat:1 SizeLat:1 for: %a128 = and i128 undef, undef
; CHECK-NEXT: Cost Model: Found costs of RThru:2 CodeSize:1 Lat:1 SizeLat:1 for: %c128 = icmp eq i128 %a128, 0
; CHECK-NEXT: Cost Model: Found costs of 1 for: %av16i8 = and <16 x i8> undef, undef
Expand All @@ -62,7 +70,7 @@ define void @andcmp() {
; CHECK-NEXT: Cost Model: Found costs of 1 for: %av4i32 = and <4 x i32> undef, undef
; CHECK-NEXT: Cost Model: Found costs of 1 for: %cv4i32 = icmp ne <4 x i32> %av4i32, zeroinitializer
; CHECK-NEXT: Cost Model: Found costs of 1 for: %c32not0 = icmp eq i32 %a32, 1
; CHECK-NEXT: Cost Model: Found costs of 1 for: %c64sle = icmp sle i64 %a64, 0
; CHECK-NEXT: Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: %c64sle = icmp sle i64 %a64, 0
; CHECK-NEXT: Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: ret void
;
%a8 = and i8 undef, undef
Expand All @@ -73,6 +81,17 @@ define void @andcmp() {
%c32 = icmp eq i32 %a32, 0
%a64 = and i64 undef, undef
%c64 = icmp ne i64 %a64, 0

%c32ge = icmp sge i32 %a32, 1
%c32le = icmp slt i32 %a32, 1
%c32leneg = icmp sle i32 %a32, -1
%c32gtneg = icmp sgt i32 %a32, -1

%c64ge = icmp sge i64 %a64, 1
%c64le = icmp slt i64 %a64, 1
%c64leneg = icmp sle i64 %a64, -1
%c64gtneg = icmp sgt i64 %a64, -1

%a128 = and i128 undef, undef
%c128 = icmp eq i128 %a128, zeroinitializer
%av16i8 = and <16 x i8> undef, undef
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