- Teach SelectionDAG::isKnownNeverZero to return true (op x, c) when c is

  non-zero.
- Teach X86 cmov optimization to eliminate the cmov from ctlz, cttz extension
  when the source of X86ISD::BSR / X86ISD::BSF is proven to be non-zero.

rdar://9490949

llvm-svn: 131948

1 files changed, 15 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/clz.ll b/llvm/test/CodeGen/X86/clz.ll
index 623ac75b529..d76fab4123b 100644
--- a/llvm/test/CodeGen/X86/clz.ll
+++ b/llvm/test/CodeGen/X86/clz.ll
@@ -31,3 +31,18 @@ entry:
 }
 
 declare i16 @llvm.ctlz.i16(i16) nounwind readnone 
+
+; Don't generate the cmovne when the source is known non-zero (and bsr would
+; not set ZF).
+; rdar://9490949
+
+define i32 @t4(i32 %n) nounwind {
+entry:
+; CHECK: t4:
+; CHECK: bsrl
+; CHECK-NOT: cmov
+; CHECK: ret
+  %or = or i32 %n, 1
+  %tmp1 = tail call i32 @llvm.ctlz.i32(i32 %or)
+  ret i32 %tmp1
+}