[llvm] 356cdab - [SimplifyCFG] avoid illegal phi with both poison and undef
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Sat Feb 27 06:58:42 PST 2021
Author: Sanjay Patel
Date: 2021-02-27T09:10:32-05:00
New Revision: 356cdabd3a9e0ff919ea2c1a35c8706ecb915297
URL: https://github.com/llvm/llvm-project/commit/356cdabd3a9e0ff919ea2c1a35c8706ecb915297
DIFF: https://github.com/llvm/llvm-project/commit/356cdabd3a9e0ff919ea2c1a35c8706ecb915297.diff
LOG: [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
Added:
llvm/test/Transforms/SimplifyCFG/poison-merge.ll
Modified:
llvm/lib/Transforms/Utils/Local.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 971f4a137bff..7c5321c4a4f7 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -918,6 +918,7 @@ static void gatherIncomingValuesToPhi(PHINode *PN,
/// \param IncomingValues A map from block to value.
static void replaceUndefValuesInPhi(PHINode *PN,
const IncomingValueMap &IncomingValues) {
+ SmallVector<unsigned> TrueUndefOps;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Value *V = PN->getIncomingValue(i);
@@ -925,10 +926,31 @@ static void replaceUndefValuesInPhi(PHINode *PN,
BasicBlock *BB = PN->getIncomingBlock(i);
IncomingValueMap::const_iterator It = IncomingValues.find(BB);
- if (It == IncomingValues.end()) continue;
+ // Keep track of undef/poison incoming values. Those must match, so we fix
+ // them up below if needed.
+ // Note: this is conservatively correct, but we could try harder and group
+ // the undef values per incoming basic block.
+ if (It == IncomingValues.end()) {
+ TrueUndefOps.push_back(i);
+ continue;
+ }
+
+ // There is a defined value for this incoming block, so map this undef
+ // incoming value to the defined value.
PN->setIncomingValue(i, It->second);
}
+
+ // If there are both undef and poison values incoming, then convert those
+ // values to undef. It is invalid to have
diff erent values for the same
+ // incoming block.
+ unsigned PoisonCount = count_if(TrueUndefOps, [&](unsigned i) {
+ return isa<PoisonValue>(PN->getIncomingValue(i));
+ });
+ if (PoisonCount != 0 && PoisonCount != TrueUndefOps.size()) {
+ for (unsigned i : TrueUndefOps)
+ PN->setIncomingValue(i, UndefValue::get(PN->getType()));
+ }
}
/// Replace a value flowing from a block to a phi with
diff --git a/llvm/test/Transforms/SimplifyCFG/poison-merge.ll b/llvm/test/Transforms/SimplifyCFG/poison-merge.ll
new file mode 100644
index 000000000000..93d9b0b299a6
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/poison-merge.ll
@@ -0,0 +1,200 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -simplifycfg -simplifycfg-require-and-preserve-domtree=1 -keep-loops=0 < %s | FileCheck %s
+
+; Merge 2 undefined incoming values.
+
+define i32 @undef_merge(i32 %x) {
+; CHECK-LABEL: @undef_merge(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: switch i32 [[X:%.*]], label [[EXIT:%.*]] [
+; CHECK-NEXT: i32 4, label [[G:%.*]]
+; CHECK-NEXT: i32 12, label [[G]]
+; CHECK-NEXT: ]
+; CHECK: g:
+; CHECK-NEXT: [[K3:%.*]] = phi i64 [ undef, [[ENTRY:%.*]] ], [ [[K3]], [[G]] ], [ undef, [[ENTRY]] ]
+; CHECK-NEXT: br label [[G]]
+; CHECK: exit:
+; CHECK-NEXT: ret i32 undef
+;
+entry:
+ switch i32 %x, label %exit [
+ i32 4, label %loop
+ i32 12, label %g
+ ]
+
+loop:
+ %k2 = phi i64 [ %k3, %g ], [ undef, %entry ]
+ br label %g
+
+g:
+ %k3 = phi i64 [ %k2, %loop ], [ undef, %entry ]
+ br label %loop
+
+exit:
+ ret i32 undef
+}
+
+; Merge 2 poison incoming values.
+
+define i32 @poison_merge(i32 %x) {
+; CHECK-LABEL: @poison_merge(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: switch i32 [[X:%.*]], label [[EXIT:%.*]] [
+; CHECK-NEXT: i32 4, label [[G:%.*]]
+; CHECK-NEXT: i32 12, label [[G]]
+; CHECK-NEXT: ]
+; CHECK: g:
+; CHECK-NEXT: [[K3:%.*]] = phi i64 [ poison, [[ENTRY:%.*]] ], [ [[K3]], [[G]] ], [ poison, [[ENTRY]] ]
+; CHECK-NEXT: br label [[G]]
+; CHECK: exit:
+; CHECK-NEXT: ret i32 undef
+;
+entry:
+ switch i32 %x, label %exit [
+ i32 4, label %loop
+ i32 12, label %g
+ ]
+
+loop:
+ %k2 = phi i64 [ %k3, %g ], [ poison, %entry ]
+ br label %g
+
+g:
+ %k3 = phi i64 [ %k2, %loop ], [ poison, %entry ]
+ br label %loop
+
+exit:
+ ret i32 undef
+}
+
+; Merge equal defined incoming values.
+
+define i32 @defined_merge(i32 %x) {
+; CHECK-LABEL: @defined_merge(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: switch i32 [[X:%.*]], label [[EXIT:%.*]] [
+; CHECK-NEXT: i32 4, label [[G:%.*]]
+; CHECK-NEXT: i32 12, label [[G]]
+; CHECK-NEXT: ]
+; CHECK: g:
+; CHECK-NEXT: [[K3:%.*]] = phi i64 [ 42, [[ENTRY:%.*]] ], [ [[K3]], [[G]] ], [ 42, [[ENTRY]] ]
+; CHECK-NEXT: br label [[G]]
+; CHECK: exit:
+; CHECK-NEXT: ret i32 undef
+;
+entry:
+ switch i32 %x, label %exit [
+ i32 4, label %loop
+ i32 12, label %g
+ ]
+
+loop:
+ %k2 = phi i64 [ %k3, %g ], [ 42, %entry ]
+ br label %g
+
+g:
+ %k3 = phi i64 [ %k2, %loop ], [ 42, %entry ]
+ br label %loop
+
+exit:
+ ret i32 undef
+}
+
+; Merge defined and undef incoming values.
+
+define i32 @defined_and_undef_merge(i32 %x) {
+; CHECK-LABEL: @defined_and_undef_merge(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: switch i32 [[X:%.*]], label [[EXIT:%.*]] [
+; CHECK-NEXT: i32 4, label [[G:%.*]]
+; CHECK-NEXT: i32 12, label [[G]]
+; CHECK-NEXT: ]
+; CHECK: g:
+; CHECK-NEXT: [[K3:%.*]] = phi i64 [ 42, [[ENTRY:%.*]] ], [ [[K3]], [[G]] ], [ 42, [[ENTRY]] ]
+; CHECK-NEXT: br label [[G]]
+; CHECK: exit:
+; CHECK-NEXT: ret i32 undef
+;
+entry:
+ switch i32 %x, label %exit [
+ i32 4, label %loop
+ i32 12, label %g
+ ]
+
+loop:
+ %k2 = phi i64 [ %k3, %g ], [ undef, %entry ]
+ br label %g
+
+g:
+ %k3 = phi i64 [ %k2, %loop ], [ 42, %entry ]
+ br label %loop
+
+exit:
+ ret i32 undef
+}
+
+; Merge defined and poison incoming values.
+
+define i32 @defined_and_poison_merge(i32 %x) {
+; CHECK-LABEL: @defined_and_poison_merge(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: switch i32 [[X:%.*]], label [[EXIT:%.*]] [
+; CHECK-NEXT: i32 4, label [[G:%.*]]
+; CHECK-NEXT: i32 12, label [[G]]
+; CHECK-NEXT: ]
+; CHECK: g:
+; CHECK-NEXT: [[K3:%.*]] = phi i64 [ 42, [[ENTRY:%.*]] ], [ [[K3]], [[G]] ], [ 42, [[ENTRY]] ]
+; CHECK-NEXT: br label [[G]]
+; CHECK: exit:
+; CHECK-NEXT: ret i32 undef
+;
+entry:
+ switch i32 %x, label %exit [
+ i32 4, label %loop
+ i32 12, label %g
+ ]
+
+loop:
+ %k2 = phi i64 [ %k3, %g ], [ poison, %entry ]
+ br label %g
+
+g:
+ %k3 = phi i64 [ %k2, %loop ], [ 42, %entry ]
+ br label %loop
+
+exit:
+ ret i32 undef
+}
+
+; Do not crash trying to merge poison and undef into a single phi.
+
+define i32 @PR49218(i32 %x) {
+; CHECK-LABEL: @PR49218(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: switch i32 [[X:%.*]], label [[EXIT:%.*]] [
+; CHECK-NEXT: i32 4, label [[G:%.*]]
+; CHECK-NEXT: i32 12, label [[G]]
+; CHECK-NEXT: ]
+; CHECK: g:
+; CHECK-NEXT: [[K3:%.*]] = phi i64 [ undef, [[ENTRY:%.*]] ], [ [[K3]], [[G]] ], [ undef, [[ENTRY]] ]
+; CHECK-NEXT: br label [[G]]
+; CHECK: exit:
+; CHECK-NEXT: ret i32 undef
+;
+entry:
+ switch i32 %x, label %exit [
+ i32 4, label %loop
+ i32 12, label %g
+ ]
+
+loop:
+ %k2 = phi i64 [ %k3, %g ], [ undef, %entry ]
+ br label %g
+
+g:
+ %k3 = phi i64 [ %k2, %loop ], [ poison, %entry ]
+ br label %loop
+
+exit:
+ ret i32 undef
+}
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