Fold bswap(undef) to undef.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96432 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/ConstantFolding.cpp b/lib/Analysis/ConstantFolding.cpp
index 6bab5eca20033e64e6d5aaac3c136b17f3767cf6..676a8466ac286f15199b0267f118af494d020d2f 100644 (file)
--- a/lib/Analysis/ConstantFolding.cpp
+++ b/lib/Analysis/ConstantFolding.cpp
@@ -1179,6 +1179,12 @@ llvm::ConstantFoldCall(Function *F,
       return 0;
     }
     
+    if (isa<UndefValue>(Operands[0])) {
+      if (Name.startswith("llvm.bswap"))
+        return Operands[0];
+      return 0;
+    }
+
     return 0;
   }
   

diff --git a/test/Transforms/InstCombine/bswap-fold.ll b/test/Transforms/InstCombine/bswap-fold.ll
index 034c70e400cee15c86b29c9b01fd5c39cf5730e1..a6b30c053eb66634551735c1c8f7e3ebfb095d4b 100644 (file)
--- a/test/Transforms/InstCombine/bswap-fold.ll
+++ b/test/Transforms/InstCombine/bswap-fold.ll
@@ -67,3 +67,9 @@ define i16 @test8(i64 %A) {
   %D = tail call i16 @llvm.bswap.i16(i16 %C) nounwind
   ret i16 %D
 }
+
+; Misc: Fold bswap(undef) to undef.
+define i64 @foo() {
+  %a = call i64 @llvm.bswap.i64(i64 undef)
+  ret i64 %a
+}