sext(undef) = 0, because the top bits will all be the same.
zext(undef) = 0, because the top bits will be zero.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127649 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index bcb0ffe..c2711c8 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2483,7 +2483,8 @@
if (OpOpcode == ISD::SIGN_EXTEND || OpOpcode == ISD::ZERO_EXTEND)
return getNode(OpOpcode, DL, VT, Operand.getNode()->getOperand(0));
else if (OpOpcode == ISD::UNDEF)
- return getUNDEF(VT);
+ // sext(undef) = 0, because the top bits will all be the same.
+ return getConstant(0, VT);
break;
case ISD::ZERO_EXTEND:
assert(VT.isInteger() && Operand.getValueType().isInteger() &&
@@ -2498,6 +2499,9 @@
if (OpOpcode == ISD::ZERO_EXTEND) // (zext (zext x)) -> (zext x)
return getNode(ISD::ZERO_EXTEND, DL, VT,
Operand.getNode()->getOperand(0));
+ else if (OpOpcode == ISD::UNDEF)
+ // zext(undef) = 0, because the top bits will be zero.
+ return getConstant(0, VT);
break;
case ISD::ANY_EXTEND:
assert(VT.isInteger() && Operand.getValueType().isInteger() &&
diff --git a/test/CodeGen/X86/machine-cse.ll b/test/CodeGen/X86/machine-cse.ll
index e284776..d819fc8 100644
--- a/test/CodeGen/X86/machine-cse.ll
+++ b/test/CodeGen/X86/machine-cse.ll
@@ -6,11 +6,11 @@
%struct.s2 = type { i32, i8*, i8*, [256 x %struct.s1*], [8 x i32], i64, i8*, i32, i64, i64, i32, %struct.s3*, %struct.s3*, [49 x i64] }
%struct.s3 = type { %struct.s3*, %struct.s3*, i32, i32, i32 }
-define fastcc i8* @t(i64 %size) nounwind {
+define fastcc i8* @t(i32 %base) nounwind {
entry:
; CHECK: t:
; CHECK: leaq (%rax,%rax,4)
- %0 = zext i32 undef to i64
+ %0 = zext i32 %base to i64
%1 = getelementptr inbounds %struct.s2* null, i64 %0
br i1 undef, label %bb1, label %bb2