[ConstantFold] Handle same type in ConstantFoldLoadThroughBitcast

Usually the case where the types are the same ends up being handled fine because it's legal to do a trivial bitcast to the same type. However, this is not true for aggregate types. Short-circuit the whole code if the types match exactly to account for this.
llvm · Dec 10, 2021 · 65bec04 · 65bec04
1 parent 5082c33
commit 65bec04
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Showing 2 changed files with 4 additions and 2 deletions.
diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -352,6 +352,9 @@ Constant *llvm::ConstantFoldLoadThroughBitcast(Constant *C, Type *DestTy,
                                          const DataLayout &DL) {
   do {
     Type *SrcTy = C->getType();
+    if (SrcTy == DestTy)
+      return C;
+
     TypeSize DestSize = DL.getTypeSizeInBits(DestTy);
     TypeSize SrcSize = DL.getTypeSizeInBits(SrcTy);
     if (!TypeSize::isKnownGE(SrcSize, DestSize))

diff --git a/llvm/test/Transforms/InstSimplify/ConstProp/loads.ll b/llvm/test/Transforms/InstSimplify/ConstProp/loads.ll
@@ -275,8 +275,7 @@ define {}* @test_trailing_zero_gep_index() {
 
 define { i64, i64 } @test_load_struct() {
 ; CHECK-LABEL: @test_load_struct(
-; CHECK-NEXT:    [[V:%.*]] = load { i64, i64 }, { i64, i64 }* @g3, align 8
-; CHECK-NEXT:    ret { i64, i64 } [[V]]
+; CHECK-NEXT:    ret { i64, i64 } { i64 123, i64 112312312 }
 ;
   %v = load { i64, i64 }, { i64, i64 }* @g3
   ret { i64, i64 } %v