[AArch64] canCreateUndefOrPoisonForTargetNode - AArch64ISD::MOVI opcodes can't create undef/poison #149323
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…des can't create undef/poison Possible fix for failed fold in llvm#148191
RKSimon
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Jul 17, 2025
| case AArch64ISD::MOVIedit: | ||
| case AArch64ISD::MOVImsl: | ||
| case AArch64ISD::MOVIshift: | ||
| case AArch64ISD::MVNIshift: |
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In fact I think these can be put into a AArch64TargetLowering::isGuaranteedNotToBeUndefOrPoisonForTargetNode implementation, but this should have the same effect
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That sounds OK to me, they should never be poison. Do we have a standard way of creating tests for changes like this?
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It might be that #148191 is the first case where we manage to show the problem (we need a case where the freeze needs removing quite late into lowering) - I haven't had time to investigate though.
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…'t create undef/poison We can always fold freeze(vashr(x,y)) -> vashr(freeze(x),freeze(y)) as VASHR has defined behaviour for out-of-range shift amounts. Test coverage can be tricky, so I've hijacked a ComputeNumSignBits test to show that value tracking can still analyse the VASHR node as the FREEZE will have been discarded by the canCreateUndefOrPoison/isGuaranteedNotToBeUndefOrPoison logic in getFreeze(). If this AArch64SelectionDAGTest.cpp approach is OK I'm intending to use it in llvm#149323 once llvm#155696 has landed.
… the freeze will be removed.
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@davemgreen I've added test coverage similar to what I'm attempting on #156445 |
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Sounds great, thanks. LGTM
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@llvm/pr-subscribers-backend-aarch64 Author: Simon Pilgrim (RKSimon) ChangesPossible fix for failed fold in #148191 Full diff: https://github.com/llvm/llvm-project/pull/149323.diff 3 Files Affected:
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index d3515cf81f443..f59cb9c5c6770 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -30959,6 +30959,24 @@ bool AArch64TargetLowering::SimplifyDemandedBitsForTargetNode(
Op, OriginalDemandedBits, OriginalDemandedElts, Known, TLO, Depth);
}
+bool AArch64TargetLowering::canCreateUndefOrPoisonForTargetNode(
+ SDValue Op, const APInt &DemandedElts, const SelectionDAG &DAG,
+ bool PoisonOnly, bool ConsiderFlags, unsigned Depth) const {
+
+ // TODO: Add more target nodes.
+ switch (Op.getOpcode()) {
+ case AArch64ISD::MOVI:
+ case AArch64ISD::MOVIedit:
+ case AArch64ISD::MOVImsl:
+ case AArch64ISD::MOVIshift:
+ case AArch64ISD::MVNImsl:
+ case AArch64ISD::MVNIshift:
+ return false;
+ }
+ return TargetLowering::canCreateUndefOrPoisonForTargetNode(
+ Op, DemandedElts, DAG, PoisonOnly, ConsiderFlags, Depth);
+}
+
bool AArch64TargetLowering::isTargetCanonicalConstantNode(SDValue Op) const {
return Op.getOpcode() == AArch64ISD::DUP ||
Op.getOpcode() == AArch64ISD::MOVI ||
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.h b/llvm/lib/Target/AArch64/AArch64ISelLowering.h
index b840af36be7e7..1988ee82880a8 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.h
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.h
@@ -869,6 +869,12 @@ class AArch64TargetLowering : public TargetLowering {
TargetLoweringOpt &TLO,
unsigned Depth) const override;
+ bool canCreateUndefOrPoisonForTargetNode(SDValue Op,
+ const APInt &DemandedElts,
+ const SelectionDAG &DAG,
+ bool PoisonOnly, bool ConsiderFlags,
+ unsigned Depth) const override;
+
bool isTargetCanonicalConstantNode(SDValue Op) const override;
// With the exception of data-predicate transitions, no instructions are
diff --git a/llvm/unittests/Target/AArch64/AArch64SelectionDAGTest.cpp b/llvm/unittests/Target/AArch64/AArch64SelectionDAGTest.cpp
index 18c8d4a69e7a8..c4cbd4f7015e6 100644
--- a/llvm/unittests/Target/AArch64/AArch64SelectionDAGTest.cpp
+++ b/llvm/unittests/Target/AArch64/AArch64SelectionDAGTest.cpp
@@ -319,6 +319,7 @@ TEST_F(AArch64SelectionDAGTest, ComputeKnownBits_UADDO_CARRY) {
}
// Piggy-backing on the AArch64 tests to verify SelectionDAG::computeKnownBits.
+// Attempt to FREEZE the MOV/MVN nodes to show that they can still be analysed.
TEST_F(AArch64SelectionDAGTest, ComputeKnownBits_MOVI) {
SDLoc Loc;
auto IntSca32VT = MVT::i32;
@@ -344,6 +345,11 @@ TEST_F(AArch64SelectionDAGTest, ComputeKnownBits_MOVI) {
EXPECT_EQ(Known.Zero, APInt(64, 0x00FF00FFFF00FF00));
EXPECT_EQ(Known.One, APInt(64, 0xFF00FF0000FF00FF));
+ auto FrMOVIedit128 = DAG->getFreeze(OpMOVIedit128);
+ Known = DAG->computeKnownBits(FrMOVIedit128);
+ EXPECT_EQ(Known.Zero, APInt(64, 0x00FF00FFFF00FF00));
+ EXPECT_EQ(Known.One, APInt(64, 0xFF00FF0000FF00FF));
+
auto N264 = DAG->getConstant(264, Loc, IntSca32VT);
auto OpMOVImsl64 =
DAG->getNode(AArch64ISD::MOVImsl, Loc, Int2Vec32VT, N165, N264);
@@ -358,6 +364,11 @@ TEST_F(AArch64SelectionDAGTest, ComputeKnownBits_MOVI) {
EXPECT_EQ(Known.Zero, APInt(32, 0xFF5A0000));
EXPECT_EQ(Known.One, APInt(32, 0x00A5FFFF));
+ auto FrMOVImsl128 = DAG->getFreeze(OpMOVImsl128);
+ Known = DAG->computeKnownBits(FrMOVImsl128);
+ EXPECT_EQ(Known.Zero, APInt(32, 0xFF5A0000));
+ EXPECT_EQ(Known.One, APInt(32, 0x00A5FFFF));
+
auto OpMVNImsl64 =
DAG->getNode(AArch64ISD::MVNImsl, Loc, Int2Vec32VT, N165, N272);
Known = DAG->computeKnownBits(OpMVNImsl64);
@@ -370,6 +381,11 @@ TEST_F(AArch64SelectionDAGTest, ComputeKnownBits_MOVI) {
EXPECT_EQ(Known.Zero, APInt(32, 0x0000A5FF));
EXPECT_EQ(Known.One, APInt(32, 0xFFFF5A00));
+ auto FrMVNImsl128 = DAG->getFreeze(OpMVNImsl128);
+ Known = DAG->computeKnownBits(FrMVNImsl128);
+ EXPECT_EQ(Known.Zero, APInt(32, 0x0000A5FF));
+ EXPECT_EQ(Known.One, APInt(32, 0xFFFF5A00));
+
auto N0 = DAG->getConstant(0, Loc, IntSca32VT);
auto OpMOVIshift2Vec32 =
DAG->getNode(AArch64ISD::MOVIshift, Loc, Int2Vec32VT, N165, N0);
@@ -384,6 +400,11 @@ TEST_F(AArch64SelectionDAGTest, ComputeKnownBits_MOVI) {
EXPECT_EQ(Known.Zero, APInt(32, 0x5AFFFFFF));
EXPECT_EQ(Known.One, APInt(32, 0xA5000000));
+ auto FrMOVIshift4Vec32 = DAG->getFreeze(OpMOVIshift4Vec32);
+ Known = DAG->computeKnownBits(FrMOVIshift4Vec32);
+ EXPECT_EQ(Known.Zero, APInt(32, 0x5AFFFFFF));
+ EXPECT_EQ(Known.One, APInt(32, 0xA5000000));
+
auto OpMVNIshift2Vec32 =
DAG->getNode(AArch64ISD::MVNIshift, Loc, Int2Vec32VT, N165, N24);
Known = DAG->computeKnownBits(OpMVNIshift2Vec32);
@@ -396,6 +417,11 @@ TEST_F(AArch64SelectionDAGTest, ComputeKnownBits_MOVI) {
EXPECT_EQ(Known.Zero, APInt(32, 0x000000A5));
EXPECT_EQ(Known.One, APInt(32, 0xFFFFFF5A));
+ auto FrMVNIshift4Vec32 = DAG->getFreeze(OpMVNIshift4Vec32);
+ Known = DAG->computeKnownBits(FrMVNIshift4Vec32);
+ EXPECT_EQ(Known.Zero, APInt(32, 0x000000A5));
+ EXPECT_EQ(Known.One, APInt(32, 0xFFFFFF5A));
+
auto N8 = DAG->getConstant(8, Loc, IntSca32VT);
auto OpMOVIshift4Vec16 =
DAG->getNode(AArch64ISD::MOVIshift, Loc, Int4Vec16VT, N165, N0);
@@ -409,6 +435,11 @@ TEST_F(AArch64SelectionDAGTest, ComputeKnownBits_MOVI) {
EXPECT_EQ(Known.Zero, APInt(16, 0x5AFF));
EXPECT_EQ(Known.One, APInt(16, 0xA500));
+ auto FrMOVIshift8Vec16 = DAG->getFreeze(OpMOVIshift8Vec16);
+ Known = DAG->computeKnownBits(FrMOVIshift8Vec16);
+ EXPECT_EQ(Known.Zero, APInt(16, 0x5AFF));
+ EXPECT_EQ(Known.One, APInt(16, 0xA500));
+
auto OpMVNIshift4Vec16 =
DAG->getNode(AArch64ISD::MVNIshift, Loc, Int4Vec16VT, N165, N8);
Known = DAG->computeKnownBits(OpMVNIshift4Vec16);
@@ -421,6 +452,11 @@ TEST_F(AArch64SelectionDAGTest, ComputeKnownBits_MOVI) {
EXPECT_EQ(Known.Zero, APInt(16, 0x00A5));
EXPECT_EQ(Known.One, APInt(16, 0xFF5A));
+ auto FrMVNIshift8Vec16 = DAG->getFreeze(OpMVNIshift8Vec16);
+ Known = DAG->computeKnownBits(FrMVNIshift8Vec16);
+ EXPECT_EQ(Known.Zero, APInt(16, 0x00A5));
+ EXPECT_EQ(Known.One, APInt(16, 0xFF5A));
+
auto OpMOVI8Vec8 = DAG->getNode(AArch64ISD::MOVI, Loc, Int8Vec8VT, N165);
Known = DAG->computeKnownBits(OpMOVI8Vec8);
EXPECT_EQ(Known.Zero, APInt(8, 0x5A));
@@ -430,6 +466,11 @@ TEST_F(AArch64SelectionDAGTest, ComputeKnownBits_MOVI) {
Known = DAG->computeKnownBits(OpMOVI16Vec8);
EXPECT_EQ(Known.Zero, APInt(8, 0x5A));
EXPECT_EQ(Known.One, APInt(8, 0xA5));
+
+ auto FrMOVI16Vec8 = DAG->getFreeze(OpMOVI16Vec8);
+ Known = DAG->computeKnownBits(FrMOVI16Vec8);
+ EXPECT_EQ(Known.Zero, APInt(8, 0x5A));
+ EXPECT_EQ(Known.One, APInt(8, 0xA5));
}
// Piggy-backing on the AArch64 tests to verify SelectionDAG::computeKnownBits.
|
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/163/builds/25881 Here is the relevant piece of the build log for the reference |
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Possible fix for failed fold in #148191