commit 9ee7123ab462d97a2b242280e9bf0b47883531cb
author Dan Gohman <gohman@apple.com> Wed Feb 17 00:54:58 2010 +0000
committer Dan Gohman <gohman@apple.com> Wed Feb 17 00:54:58 2010 +0000
tree 3588eaffa989e094b90f3caa5a668d725949a594
parent 378c0b35a7b9884f1de2a9762825424fbf1813ac

Fold bswap(undef) to undef.


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

lib/Analysis/ConstantFolding.cpp

diff --git a/lib/Analysis/ConstantFolding.cpp b/lib/Analysis/ConstantFolding.cpp
index 6bab5ec..676a846 100644
--- a/lib/Analysis/ConstantFolding.cpp
+++ b/lib/Analysis/ConstantFolding.cpp
@@ -1179,6 +1179,12 @@
       return 0;
     }
     
+    if (isa<UndefValue>(Operands[0])) {
+      if (Name.startswith("llvm.bswap"))
+        return Operands[0];
+      return 0;
+    }
+
     return 0;
   }
   

test/Transforms/InstCombine/bswap-fold.ll

diff --git a/test/Transforms/InstCombine/bswap-fold.ll b/test/Transforms/InstCombine/bswap-fold.ll
index 034c70e..a6b30c0 100644
--- a/test/Transforms/InstCombine/bswap-fold.ll
+++ b/test/Transforms/InstCombine/bswap-fold.ll
@@ -67,3 +67,9 @@
   %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
+}