[llvm] [SelectionDAG] Improve isGuaranteedNotToBeUndefOrPoison (PR #147019)
Björn Pettersson via llvm-commits
llvm-commits at lists.llvm.org
Thu Jul 17 07:55:20 PDT 2025
https://github.com/bjope updated https://github.com/llvm/llvm-project/pull/147019
>From 3d04a3b11539083519973d65db78d2595a767d54 Mon Sep 17 00:00:00 2001
From: Bjorn Pettersson <bjorn.a.pettersson at ericsson.com>
Date: Thu, 17 Jul 2025 16:32:38 +0200
Subject: [PATCH] [SelectionDAG] Improve isGuaranteedNotToBeUndefOrPoison
Add special handling of EXTRACT_SUBVECTOR, INSERT_SUBVECTOR,
EXTRACT_VECTOR_ELT, INSERT_VECTOR_ELT and SCALAR_TO_VECTOR in
isGuaranteedNotToBeUndefOrPoison. Make use of DemandedElts to
improve the analysis and only check relevant elements for each
operand.
Also start using DemandedElts in the recursive calls that
check isGuaranteedNotToBeUndefOrPoison for all operands for
operations that do not create undef/poison. We can do that for
a number of elementwise operations for which the DemandedElts
can be applied to every operand (e.g. ADD, OR, BITREVERSE, TRUNCATE).
---
.../lib/CodeGen/SelectionDAG/SelectionDAG.cpp | 123 ++++++++++++++++++
.../X86/div-rem-pair-recomposition-signed.ll | 31 +++--
llvm/test/CodeGen/X86/pr62286.ll | 14 +-
3 files changed, 146 insertions(+), 22 deletions(-)
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 682d93d0abf3f..ab39123d34dbd 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -5461,6 +5461,83 @@ bool SelectionDAG::isGuaranteedNotToBeUndefOrPoison(SDValue Op,
}
return true;
+ case ISD::EXTRACT_SUBVECTOR: {
+ SDValue Src = Op.getOperand(0);
+ if (Src.getValueType().isScalableVector())
+ break;
+ uint64_t Idx = Op.getConstantOperandVal(1);
+ unsigned NumSrcElts = Src.getValueType().getVectorNumElements();
+ APInt DemandedSrcElts = DemandedElts.zext(NumSrcElts).shl(Idx);
+ return isGuaranteedNotToBeUndefOrPoison(Src, DemandedSrcElts, PoisonOnly,
+ Depth + 1);
+ }
+
+ case ISD::INSERT_SUBVECTOR: {
+ if (Op.getValueType().isScalableVector())
+ break;
+ SDValue Src = Op.getOperand(0);
+ SDValue Sub = Op.getOperand(1);
+ uint64_t Idx = Op.getConstantOperandVal(2);
+ unsigned NumSubElts = Sub.getValueType().getVectorNumElements();
+ APInt DemandedSubElts = DemandedElts.extractBits(NumSubElts, Idx);
+ APInt DemandedSrcElts = DemandedElts;
+ DemandedSrcElts.clearBits(Idx, Idx + NumSubElts);
+
+ if (!!DemandedSubElts && !isGuaranteedNotToBeUndefOrPoison(
+ Sub, DemandedSubElts, PoisonOnly, Depth + 1))
+ return false;
+ if (!!DemandedSrcElts && !isGuaranteedNotToBeUndefOrPoison(
+ Src, DemandedSrcElts, PoisonOnly, Depth + 1))
+ return false;
+ return true;
+ }
+
+ case ISD::EXTRACT_VECTOR_ELT: {
+ SDValue Src = Op.getOperand(0);
+ auto *IndexC = dyn_cast<ConstantSDNode>(Op.getOperand(1));
+ EVT SrcVT = Src.getValueType();
+ if (SrcVT.isFixedLengthVector() && IndexC &&
+ IndexC->getAPIntValue().ult(SrcVT.getVectorNumElements())) {
+ APInt DemandedSrcElts = APInt::getOneBitSet(SrcVT.getVectorNumElements(),
+ IndexC->getZExtValue());
+ return isGuaranteedNotToBeUndefOrPoison(Src, DemandedSrcElts, PoisonOnly,
+ Depth + 1);
+ }
+ break;
+ }
+
+ case ISD::INSERT_VECTOR_ELT: {
+ SDValue InVec = Op.getOperand(0);
+ SDValue InVal = Op.getOperand(1);
+ SDValue EltNo = Op.getOperand(2);
+ EVT VT = InVec.getValueType();
+ auto *IndexC = dyn_cast<ConstantSDNode>(EltNo);
+ if (IndexC && VT.isFixedLengthVector() &&
+ IndexC->getZExtValue() < VT.getVectorNumElements()) {
+ if (DemandedElts[IndexC->getZExtValue()] &&
+ !isGuaranteedNotToBeUndefOrPoison(InVal, PoisonOnly, Depth + 1))
+ return false;
+ APInt InVecDemandedElts = DemandedElts;
+ InVecDemandedElts.clearBit(IndexC->getZExtValue());
+ if (!!InVecDemandedElts &&
+ !isGuaranteedNotToBeUndefOrPoison(InVec, InVecDemandedElts,
+ PoisonOnly, Depth + 1))
+ return false;
+ return true;
+ }
+ break;
+ }
+
+ case ISD::SCALAR_TO_VECTOR:
+ // Check upper (known undef) elements.
+ if (DemandedElts.ugt(1) && !PoisonOnly)
+ return false;
+ // Check element zero.
+ if (DemandedElts[0] && !isGuaranteedNotToBeUndefOrPoison(
+ Op.getOperand(0), PoisonOnly, Depth + 1))
+ return false;
+ return true;
+
case ISD::SPLAT_VECTOR:
return isGuaranteedNotToBeUndefOrPoison(Op.getOperand(0), PoisonOnly,
Depth + 1);
@@ -5483,6 +5560,52 @@ bool SelectionDAG::isGuaranteedNotToBeUndefOrPoison(SDValue Op,
return true;
}
+ case ISD::SHL:
+ case ISD::SRL:
+ case ISD::SRA:
+ // Shift amount operand is checked by canCreateUndefOrPoison. So it is
+ // enough to check operand 0 if Op can't create undef/poison.
+ return !canCreateUndefOrPoison(Op, DemandedElts, PoisonOnly,
+ /*ConsiderFlags*/ true, Depth) &&
+ isGuaranteedNotToBeUndefOrPoison(Op.getOperand(0), DemandedElts,
+ PoisonOnly, Depth + 1);
+
+ case ISD::BSWAP:
+ case ISD::CTPOP:
+ case ISD::BITREVERSE:
+ case ISD::AND:
+ case ISD::OR:
+ case ISD::XOR:
+ case ISD::ADD:
+ case ISD::SUB:
+ case ISD::MUL:
+ case ISD::SADDSAT:
+ case ISD::UADDSAT:
+ case ISD::SSUBSAT:
+ case ISD::USUBSAT:
+ case ISD::SSHLSAT:
+ case ISD::USHLSAT:
+ case ISD::SMIN:
+ case ISD::SMAX:
+ case ISD::UMIN:
+ case ISD::UMAX:
+ case ISD::ZERO_EXTEND:
+ case ISD::SIGN_EXTEND:
+ case ISD::ANY_EXTEND:
+ case ISD::TRUNCATE:
+ case ISD::VSELECT: {
+ // If Op can't create undef/poison and none of its operands are undef/poison
+ // then Op is never undef/poison. A difference from the more common check
+ // below, outside the switch, is that we handle elementwise operations for
+ // which the DemandedElts mask is valid for all operands here.
+ return !canCreateUndefOrPoison(Op, DemandedElts, PoisonOnly,
+ /*ConsiderFlags*/ true, Depth) &&
+ all_of(Op->ops(), [&](SDValue V) {
+ return isGuaranteedNotToBeUndefOrPoison(V, DemandedElts,
+ PoisonOnly, Depth + 1);
+ });
+ }
+
// TODO: Search for noundef attributes from library functions.
// TODO: Pointers dereferenced by ISD::LOAD/STORE ops are noundef.
diff --git a/llvm/test/CodeGen/X86/div-rem-pair-recomposition-signed.ll b/llvm/test/CodeGen/X86/div-rem-pair-recomposition-signed.ll
index 661e7bb19641c..d1a0930d8b7b3 100644
--- a/llvm/test/CodeGen/X86/div-rem-pair-recomposition-signed.ll
+++ b/llvm/test/CodeGen/X86/div-rem-pair-recomposition-signed.ll
@@ -172,10 +172,9 @@ define i128 @scalar_i128(i128 %x, i128 %y, ptr %divdst) nounwind {
; X86-NEXT: movl %esi, {{[-0-9]+}}(%e{{[sb]}}p) # 4-byte Spill
; X86-NEXT: sbbl %eax, %edi
; X86-NEXT: movl %edi, {{[-0-9]+}}(%e{{[sb]}}p) # 4-byte Spill
-; X86-NEXT: movl 52(%ebp), %ecx
-; X86-NEXT: movl %ecx, %edx
+; X86-NEXT: movl 52(%ebp), %esi
+; X86-NEXT: movl %esi, %edx
; X86-NEXT: sarl $31, %edx
-; X86-NEXT: movl %ecx, %esi
; X86-NEXT: xorl %edx, %esi
; X86-NEXT: movl 48(%ebp), %ecx
; X86-NEXT: xorl %edx, %ecx
@@ -204,14 +203,14 @@ define i128 @scalar_i128(i128 %x, i128 %y, ptr %divdst) nounwind {
; X86-NEXT: sete %al
; X86-NEXT: orb %cl, %al
; X86-NEXT: movb %al, {{[-0-9]+}}(%e{{[sb]}}p) # 1-byte Spill
-; X86-NEXT: movl {{[-0-9]+}}(%e{{[sb]}}p), %eax # 4-byte Reload
-; X86-NEXT: bsrl %eax, %edx
+; X86-NEXT: bsrl %esi, %edx
; X86-NEXT: xorl $31, %edx
-; X86-NEXT: addl $32, %edx
-; X86-NEXT: bsrl %esi, %ecx
+; X86-NEXT: movl {{[-0-9]+}}(%e{{[sb]}}p), %eax # 4-byte Reload
+; X86-NEXT: bsrl %eax, %ecx
; X86-NEXT: xorl $31, %ecx
+; X86-NEXT: addl $32, %ecx
; X86-NEXT: testl %esi, %esi
-; X86-NEXT: cmovel %edx, %ecx
+; X86-NEXT: cmovnel %edx, %ecx
; X86-NEXT: bsrl %ebx, %edx
; X86-NEXT: xorl $31, %edx
; X86-NEXT: movl %edi, {{[-0-9]+}}(%e{{[sb]}}p) # 4-byte Spill
@@ -226,14 +225,14 @@ define i128 @scalar_i128(i128 %x, i128 %y, ptr %divdst) nounwind {
; X86-NEXT: movl %esi, {{[-0-9]+}}(%e{{[sb]}}p) # 4-byte Spill
; X86-NEXT: orl %esi, %edx
; X86-NEXT: cmovnel %ecx, %edi
-; X86-NEXT: bsrl {{[-0-9]+}}(%e{{[sb]}}p), %edx # 4-byte Folded Reload
-; X86-NEXT: xorl $31, %edx
-; X86-NEXT: addl $32, %edx
; X86-NEXT: movl {{[-0-9]+}}(%e{{[sb]}}p), %eax # 4-byte Reload
-; X86-NEXT: bsrl %eax, %ecx
+; X86-NEXT: bsrl %eax, %edx
+; X86-NEXT: xorl $31, %edx
+; X86-NEXT: bsrl {{[-0-9]+}}(%e{{[sb]}}p), %ecx # 4-byte Folded Reload
; X86-NEXT: xorl $31, %ecx
+; X86-NEXT: addl $32, %ecx
; X86-NEXT: testl %eax, %eax
-; X86-NEXT: cmovel %edx, %ecx
+; X86-NEXT: cmovnel %edx, %ecx
; X86-NEXT: movl {{[-0-9]+}}(%e{{[sb]}}p), %ebx # 4-byte Reload
; X86-NEXT: bsrl %ebx, %esi
; X86-NEXT: xorl $31, %esi
@@ -380,9 +379,9 @@ define i128 @scalar_i128(i128 %x, i128 %y, ptr %divdst) nounwind {
; X86-NEXT: movl {{[-0-9]+}}(%e{{[sb]}}p), %eax # 4-byte Reload
; X86-NEXT: adcl $-1, %eax
; X86-NEXT: movl %eax, {{[-0-9]+}}(%e{{[sb]}}p) # 4-byte Spill
-; X86-NEXT: movl {{[-0-9]+}}(%e{{[sb]}}p), %eax # 4-byte Reload
-; X86-NEXT: adcl $-1, %eax
-; X86-NEXT: movl %eax, {{[-0-9]+}}(%e{{[sb]}}p) # 4-byte Spill
+; X86-NEXT: movl {{[-0-9]+}}(%e{{[sb]}}p), %ecx # 4-byte Reload
+; X86-NEXT: adcl $-1, %ecx
+; X86-NEXT: movl %ecx, {{[-0-9]+}}(%e{{[sb]}}p) # 4-byte Spill
; X86-NEXT: movl {{[-0-9]+}}(%e{{[sb]}}p), %ecx # 4-byte Reload
; X86-NEXT: adcl $-1, %ecx
; X86-NEXT: movl %ecx, {{[-0-9]+}}(%e{{[sb]}}p) # 4-byte Spill
diff --git a/llvm/test/CodeGen/X86/pr62286.ll b/llvm/test/CodeGen/X86/pr62286.ll
index 2d1b7fcbf0239..ce03f8fad4a19 100644
--- a/llvm/test/CodeGen/X86/pr62286.ll
+++ b/llvm/test/CodeGen/X86/pr62286.ll
@@ -28,8 +28,9 @@ define i64 @PR62286(i32 %a) {
; AVX1-NEXT: vmovd %edi, %xmm0
; AVX1-NEXT: vpslldq {{.*#+}} xmm1 = zero,zero,zero,zero,zero,zero,zero,zero,zero,zero,zero,zero,xmm0[0,1,2,3]
; AVX1-NEXT: vpaddd %xmm0, %xmm0, %xmm0
+; AVX1-NEXT: vpxor %xmm2, %xmm2, %xmm2
+; AVX1-NEXT: vpblendw {{.*#+}} xmm0 = xmm0[0,1],xmm2[2,3,4,5,6,7]
; AVX1-NEXT: vpand {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm1, %xmm1
-; AVX1-NEXT: vpblendw {{.*#+}} xmm0 = xmm0[0,1],xmm1[2,3,4,5,6,7]
; AVX1-NEXT: vpmovsxdq %xmm0, %xmm0
; AVX1-NEXT: vpshufd {{.*#+}} xmm1 = xmm1[2,3,2,3]
; AVX1-NEXT: vpmovsxdq %xmm1, %xmm1
@@ -58,12 +59,13 @@ define i64 @PR62286(i32 %a) {
; AVX512-LABEL: PR62286:
; AVX512: # %bb.0:
; AVX512-NEXT: vmovd %edi, %xmm0
-; AVX512-NEXT: vpshufd {{.*#+}} xmm0 = xmm0[0,1,1,0]
-; AVX512-NEXT: vpandd {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %zmm0, %zmm1
-; AVX512-NEXT: movw $4369, %ax # imm = 0x1111
+; AVX512-NEXT: movb $8, %al
; AVX512-NEXT: kmovd %eax, %k1
-; AVX512-NEXT: vpaddd %zmm0, %zmm0, %zmm1 {%k1}
-; AVX512-NEXT: vpmovsxdq %ymm1, %zmm0
+; AVX512-NEXT: vpexpandd %ymm0, %ymm1 {%k1} {z}
+; AVX512-NEXT: vpand {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm1, %ymm1
+; AVX512-NEXT: vpaddd %ymm0, %ymm0, %ymm0
+; AVX512-NEXT: vpblendd {{.*#+}} ymm0 = ymm0[0],ymm1[1,2,3],ymm0[4],ymm1[5,6,7]
+; AVX512-NEXT: vpmovsxdq %ymm0, %zmm0
; AVX512-NEXT: vextracti64x4 $1, %zmm0, %ymm1
; AVX512-NEXT: vpaddq %zmm1, %zmm0, %zmm0
; AVX512-NEXT: vextracti128 $1, %ymm0, %xmm1
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