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[SimplifyCFG] avoid illegal phi with both poison and undef
In the example based on: https://llvm.org/PR49218 ...we are crashing because poison is a subclass of undef, so we merge blocks and create: PHI node has multiple entries for the same basic block with different incoming values! %k3 = phi i64 [ poison, %entry ], [ %k3, %g ], [ undef, %entry ] If both poison and undef values are incoming, we soften the poison values to undef. Differential Revision: https://reviews.llvm.org/D97495
This commit is contained in:
Sanjay Patel
parent
80c4b80982
commit
c42cc1f879
@ -918,6 +918,7 @@ static void gatherIncomingValuesToPhi(PHINode *PN,
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/// \param IncomingValues A map from block to value.
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/// \param IncomingValues A map from block to value.
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static void replaceUndefValuesInPhi(PHINode *PN,
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static void replaceUndefValuesInPhi(PHINode *PN,
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const IncomingValueMap &IncomingValues) {
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const IncomingValueMap &IncomingValues) {
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SmallVector<unsigned> TrueUndefOps;
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for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
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for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
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Value *V = PN->getIncomingValue(i);
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Value *V = PN->getIncomingValue(i);
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@ -925,10 +926,31 @@ static void replaceUndefValuesInPhi(PHINode *PN,
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BasicBlock *BB = PN->getIncomingBlock(i);
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BasicBlock *BB = PN->getIncomingBlock(i);
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IncomingValueMap::const_iterator It = IncomingValues.find(BB);
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IncomingValueMap::const_iterator It = IncomingValues.find(BB);
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if (It == IncomingValues.end()) continue;
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// Keep track of undef/poison incoming values. Those must match, so we fix
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// them up below if needed.
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// Note: this is conservatively correct, but we could try harder and group
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// the undef values per incoming basic block.
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if (It == IncomingValues.end()) {
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TrueUndefOps.push_back(i);
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continue;
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}
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// There is a defined value for this incoming block, so map this undef
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// incoming value to the defined value.
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PN->setIncomingValue(i, It->second);
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PN->setIncomingValue(i, It->second);
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}
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}
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// If there are both undef and poison values incoming, then convert those
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// values to undef. It is invalid to have different values for the same
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// incoming block.
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unsigned PoisonCount = count_if(TrueUndefOps, [&](unsigned i) {
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return isa<PoisonValue>(PN->getIncomingValue(i));
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});
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if (PoisonCount != 0 && PoisonCount != TrueUndefOps.size()) {
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for (unsigned i : TrueUndefOps)
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PN->setIncomingValue(i, UndefValue::get(PN->getType()));
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}
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}
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}
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/// Replace a value flowing from a block to a phi with
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/// Replace a value flowing from a block to a phi with
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200
test/Transforms/SimplifyCFG/poison-merge.ll
Normal file
200
test/Transforms/SimplifyCFG/poison-merge.ll
Normal file
@ -0,0 +1,200 @@
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt -S -simplifycfg -simplifycfg-require-and-preserve-domtree=1 -keep-loops=0 < %s | FileCheck %s
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; Merge 2 undefined incoming values.
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define i32 @undef_merge(i32 %x) {
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; CHECK-LABEL: @undef_merge(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: switch i32 [[X:%.*]], label [[EXIT:%.*]] [
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; CHECK-NEXT: i32 4, label [[G:%.*]]
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; CHECK-NEXT: i32 12, label [[G]]
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; CHECK-NEXT: ]
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; CHECK: g:
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; CHECK-NEXT: [[K3:%.*]] = phi i64 [ undef, [[ENTRY:%.*]] ], [ [[K3]], [[G]] ], [ undef, [[ENTRY]] ]
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; CHECK-NEXT: br label [[G]]
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; CHECK: exit:
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; CHECK-NEXT: ret i32 undef
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;
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entry:
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switch i32 %x, label %exit [
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i32 4, label %loop
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i32 12, label %g
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]
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loop:
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%k2 = phi i64 [ %k3, %g ], [ undef, %entry ]
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br label %g
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g:
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%k3 = phi i64 [ %k2, %loop ], [ undef, %entry ]
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br label %loop
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exit:
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ret i32 undef
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}
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; Merge 2 poison incoming values.
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define i32 @poison_merge(i32 %x) {
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; CHECK-LABEL: @poison_merge(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: switch i32 [[X:%.*]], label [[EXIT:%.*]] [
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; CHECK-NEXT: i32 4, label [[G:%.*]]
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; CHECK-NEXT: i32 12, label [[G]]
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; CHECK-NEXT: ]
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; CHECK: g:
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; CHECK-NEXT: [[K3:%.*]] = phi i64 [ poison, [[ENTRY:%.*]] ], [ [[K3]], [[G]] ], [ poison, [[ENTRY]] ]
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; CHECK-NEXT: br label [[G]]
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; CHECK: exit:
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; CHECK-NEXT: ret i32 undef
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;
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entry:
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switch i32 %x, label %exit [
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i32 4, label %loop
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i32 12, label %g
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]
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loop:
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%k2 = phi i64 [ %k3, %g ], [ poison, %entry ]
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br label %g
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g:
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%k3 = phi i64 [ %k2, %loop ], [ poison, %entry ]
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br label %loop
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exit:
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ret i32 undef
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}
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; Merge equal defined incoming values.
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define i32 @defined_merge(i32 %x) {
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; CHECK-LABEL: @defined_merge(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: switch i32 [[X:%.*]], label [[EXIT:%.*]] [
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; CHECK-NEXT: i32 4, label [[G:%.*]]
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; CHECK-NEXT: i32 12, label [[G]]
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; CHECK-NEXT: ]
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; CHECK: g:
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; CHECK-NEXT: [[K3:%.*]] = phi i64 [ 42, [[ENTRY:%.*]] ], [ [[K3]], [[G]] ], [ 42, [[ENTRY]] ]
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; CHECK-NEXT: br label [[G]]
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; CHECK: exit:
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; CHECK-NEXT: ret i32 undef
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;
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entry:
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switch i32 %x, label %exit [
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i32 4, label %loop
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i32 12, label %g
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]
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loop:
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%k2 = phi i64 [ %k3, %g ], [ 42, %entry ]
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br label %g
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g:
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%k3 = phi i64 [ %k2, %loop ], [ 42, %entry ]
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br label %loop
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exit:
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ret i32 undef
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}
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; Merge defined and undef incoming values.
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define i32 @defined_and_undef_merge(i32 %x) {
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; CHECK-LABEL: @defined_and_undef_merge(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: switch i32 [[X:%.*]], label [[EXIT:%.*]] [
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; CHECK-NEXT: i32 4, label [[G:%.*]]
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; CHECK-NEXT: i32 12, label [[G]]
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; CHECK-NEXT: ]
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; CHECK: g:
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; CHECK-NEXT: [[K3:%.*]] = phi i64 [ 42, [[ENTRY:%.*]] ], [ [[K3]], [[G]] ], [ 42, [[ENTRY]] ]
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; CHECK-NEXT: br label [[G]]
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; CHECK: exit:
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; CHECK-NEXT: ret i32 undef
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;
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entry:
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switch i32 %x, label %exit [
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i32 4, label %loop
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i32 12, label %g
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]
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loop:
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%k2 = phi i64 [ %k3, %g ], [ undef, %entry ]
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br label %g
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g:
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%k3 = phi i64 [ %k2, %loop ], [ 42, %entry ]
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br label %loop
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exit:
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ret i32 undef
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}
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; Merge defined and poison incoming values.
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define i32 @defined_and_poison_merge(i32 %x) {
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; CHECK-LABEL: @defined_and_poison_merge(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: switch i32 [[X:%.*]], label [[EXIT:%.*]] [
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; CHECK-NEXT: i32 4, label [[G:%.*]]
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; CHECK-NEXT: i32 12, label [[G]]
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; CHECK-NEXT: ]
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; CHECK: g:
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; CHECK-NEXT: [[K3:%.*]] = phi i64 [ 42, [[ENTRY:%.*]] ], [ [[K3]], [[G]] ], [ 42, [[ENTRY]] ]
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; CHECK-NEXT: br label [[G]]
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; CHECK: exit:
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; CHECK-NEXT: ret i32 undef
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;
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entry:
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switch i32 %x, label %exit [
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i32 4, label %loop
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i32 12, label %g
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]
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loop:
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%k2 = phi i64 [ %k3, %g ], [ poison, %entry ]
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br label %g
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g:
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%k3 = phi i64 [ %k2, %loop ], [ 42, %entry ]
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br label %loop
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exit:
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ret i32 undef
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}
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; Do not crash trying to merge poison and undef into a single phi.
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define i32 @PR49218(i32 %x) {
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; CHECK-LABEL: @PR49218(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: switch i32 [[X:%.*]], label [[EXIT:%.*]] [
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; CHECK-NEXT: i32 4, label [[G:%.*]]
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; CHECK-NEXT: i32 12, label [[G]]
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; CHECK-NEXT: ]
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; CHECK: g:
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; CHECK-NEXT: [[K3:%.*]] = phi i64 [ undef, [[ENTRY:%.*]] ], [ [[K3]], [[G]] ], [ undef, [[ENTRY]] ]
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; CHECK-NEXT: br label [[G]]
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; CHECK: exit:
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; CHECK-NEXT: ret i32 undef
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;
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entry:
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switch i32 %x, label %exit [
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i32 4, label %loop
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i32 12, label %g
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]
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loop:
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%k2 = phi i64 [ %k3, %g ], [ undef, %entry ]
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br label %g
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g:
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%k3 = phi i64 [ %k2, %loop ], [ poison, %entry ]
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br label %loop
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exit:
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ret i32 undef
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}
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