[PATCH] D99853: [InstSimplify] Teach isUndefValue to understand const vector with both undef & poison

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune created this revision.
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A constant vector that has both undef & poison, e.g., `<i8 undef, i8 poison>`, isn't `UndefValue`.
This causes `SimplifyQuery::isUndefValue` to return false even if it is.
This patch teaches the function to recognize such form as well.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D99853

Files:
  llvm/include/llvm/Analysis/InstructionSimplify.h
  llvm/test/Transforms/InstSimplify/icmp-constant.ll


Index: llvm/test/Transforms/InstSimplify/icmp-constant.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/icmp-constant.ll
+++ llvm/test/Transforms/InstSimplify/icmp-constant.ll
@@ -1069,8 +1069,7 @@
 
 define <2 x i1> @heterogeneous_constvector(<2 x i8> %x) {
 ; CHECK-LABEL: @heterogeneous_constvector(
-; CHECK-NEXT:    [[C:%.*]] = icmp ult <2 x i8> [[X:%.*]], <i8 undef, i8 poison>
-; CHECK-NEXT:    ret <2 x i1> [[C]]
+; CHECK-NEXT:    ret <2 x i1> zeroinitializer
 ;
   %c = icmp ult <2 x i8> %x, <i8 undef, i8 poison>
   ret <2 x i1> %c
Index: llvm/include/llvm/Analysis/InstructionSimplify.h
===================================================================
--- llvm/include/llvm/Analysis/InstructionSimplify.h
+++ llvm/include/llvm/Analysis/InstructionSimplify.h
@@ -133,7 +133,22 @@
   bool isUndefValue(Value *V) const {
     if (!CanUseUndef)
       return false;
-    return isa<UndefValue>(V);
+
+    if (isa<UndefValue>(V))
+      return true;
+
+    // Check whether V is e.g., <undef, poison>
+    Constant *C = dyn_cast<Constant>(V);
+    auto *FVTy = dyn_cast<FixedVectorType>(V->getType());
+    if (C && FVTy) {
+      for (unsigned i = 0, e = FVTy->getNumElements(); i != e; ++i) {
+        auto *EV = C->getAggregateElement(i);
+        if (!EV || !isa<UndefValue>(EV))
+          return false;
+      }
+      return true;
+    }
+    return false;
   }
 };
 


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