SimplifyLibcalls: The return value of ffsll is always i32, even when the input is zero.

Fixes PR13028.

llvm-svn: 166313

2 files changed, 14 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp
index 90efa8ae0e0..c82a00fc2c8 100644
--- a/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp
@@ -772,8 +772,8 @@ struct FFSOpt : public LibCallOptimization {
 
     // Constant fold.
     if (ConstantInt *CI = dyn_cast<ConstantInt>(Op)) {
-      if (CI->getValue() == 0)  // ffs(0) -> 0.
-        return Constant::getNullValue(CI->getType());
+      if (CI->isZero()) // ffs(0) -> 0.
+        return B.getInt32(0);
       // ffs(c) -> cttz(c)+1
       return B.getInt32(CI->getValue().countTrailingZeros() + 1);
     }
diff --git a/llvm/test/Transforms/SimplifyLibCalls/FFS.ll b/llvm/test/Transforms/SimplifyLibCalls/FFS.ll
index e38d78349d4..6aecbeacd7e 100644
--- a/llvm/test/Transforms/SimplifyLibCalls/FFS.ll
+++ b/llvm/test/Transforms/SimplifyLibCalls/FFS.ll
@@ -1,6 +1,7 @@
-; Test that the ToAsciiOptimizer works correctly
-; RUN: opt < %s -simplify-libcalls -S | \
-; RUN:   not grep "call.*@ffs"
+; Test that FFSOpt works correctly
+; RUN: opt < %s -simplify-libcalls -S | FileCheck %s
+
+; CHECK-NOT: call{{.*}}@ffs
 
 @non_const = external global i32		; <i32*> [#uses=1]
 
@@ -34,3 +35,11 @@ define i32 @a(i64) nounwind {
         %2 = call i32 @ffsll(i64 %0)            ; <i32> [#uses=1]
         ret i32 %2
 }
+
+; PR13028
+define i32 @b() nounwind {
+  %ffs = call i32 @ffsll(i64 0)
+  ret i32 %ffs
+; CHECK: @b
+; CHECK-NEXT: ret i32 0
+}