[PATCH] D86396: [Attributor] Change AANoUndef not to deduce noundef for dead returned positions

[Shinji Okumura via Phabricator via llvm-commits]

okura created this revision.
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When a returned position is dead, returned values will be replaced with undef values by AAIsDead.
Therefore we should not deduce noundef for the position. Otherwise, AAUndefinedBehavior caught that and replace them with `unreachable` incorrectly.


https://reviews.llvm.org/D86396

Files:
  llvm/lib/Transforms/IPO/AttributorAttributes.cpp
  llvm/test/Transforms/Attributor/noundef.ll


Index: llvm/test/Transforms/Attributor/noundef.ll
===================================================================
--- llvm/test/Transforms/Attributor/noundef.ll
+++ llvm/test/Transforms/Attributor/noundef.ll
@@ -20,3 +20,21 @@
   call void @bar(i32* %x)
   ret void
 }
+
+define internal i8* @returned_dead() {
+; CHECK-LABEL: define internal noalias align 536870912 i8* @returned_dead(
+; CHECK-NEXT:    call void @unknown()
+; CHECK-NEXT:    ret i8* undef
+;
+  call void @unknown()
+  ret i8* null
+}
+
+define void @caller() {
+; CHECK-LABEL: @caller(
+; CHECK-NEXT:    [[TMP1:%.*]] = call i8* @returned_dead()
+; CHECK-NEXT:    ret void
+;
+  call i8* @returned_dead()
+  ret void
+}
Index: llvm/lib/Transforms/IPO/AttributorAttributes.cpp
===================================================================
--- llvm/lib/Transforms/IPO/AttributorAttributes.cpp
+++ llvm/lib/Transforms/IPO/AttributorAttributes.cpp
@@ -7786,8 +7786,18 @@
 
 struct AANoUndefReturned final
     : AAReturnedFromReturnedValues<AANoUndef, AANoUndefImpl> {
-  AANoUndefReturned(const IRPosition &IRP, Attributor &A)
-      : AAReturnedFromReturnedValues<AANoUndef, AANoUndefImpl>(IRP, A) {}
+  using Base = AAReturnedFromReturnedValues<AANoUndef, AANoUndefImpl>;
+  AANoUndefReturned(const IRPosition &IRP, Attributor &A) : Base(IRP, A) {}
+
+  /// See AbstractAttribute::updateImpl(...).
+  ChangeStatus updateImpl(Attributor &A) override {
+    auto &LivenessAA = A.getAAFor<AAIsDead>(*this, getIRPosition());
+    // When the returned position is dead, returned values will be replaced with
+    // undef values by AAIsDead. So we don't deduce noundef for this position.
+    if (LivenessAA.isKnown())
+      return indicatePessimisticFixpoint();
+    return Base::updateImpl(A);
+  }
 
   /// See AbstractAttribute::trackStatistics()
   void trackStatistics() const override { STATS_DECLTRACK_FNRET_ATTR(noundef) }


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