Handle a special case xor undef, undef -> 0. Technically this should be transformed to undef. But this is such a common idiom (misuse) we are going to handle it.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48792 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 2229743..e24a294 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2119,6 +2119,9 @@
if (FoldedVOp.Val) return FoldedVOp;
}
+ // fold (xor undef, undef) -> 0. This is a common idiom (misuse).
+ if (N0.getOpcode() == ISD::UNDEF && N1.getOpcode() == ISD::UNDEF)
+ return DAG.getConstant(0, VT);
// fold (xor x, undef) -> undef
if (N0.getOpcode() == ISD::UNDEF)
return N0;
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 05f7edb..ed564b2 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2245,6 +2245,12 @@
// Fold a bunch of operators when the RHS is undef.
if (N2.getOpcode() == ISD::UNDEF) {
switch (Opcode) {
+ case ISD::XOR:
+ if (N1.getOpcode() == ISD::UNDEF)
+ // Handle undef ^ undef -> 0 special case. This is a common
+ // idiom (misuse).
+ return getConstant(0, VT);
+ // fallthrough
case ISD::ADD:
case ISD::ADDC:
case ISD::ADDE:
@@ -2258,7 +2264,6 @@
case ISD::SDIV:
case ISD::UREM:
case ISD::SREM:
- case ISD::XOR:
return N2; // fold op(arg1, undef) -> undef
case ISD::MUL:
case ISD::AND:
diff --git a/lib/VMCore/ConstantFold.cpp b/lib/VMCore/ConstantFold.cpp
index 762a24a..7b21817 100644
--- a/lib/VMCore/ConstantFold.cpp
+++ b/lib/VMCore/ConstantFold.cpp
@@ -474,9 +474,14 @@
// Handle UndefValue up front
if (isa<UndefValue>(C1) || isa<UndefValue>(C2)) {
switch (Opcode) {
+ case Instruction::Xor:
+ if (isa<UndefValue>(C1) && isa<UndefValue>(C2))
+ // Handle undef ^ undef -> 0 special case. This is a common
+ // idiom (misuse).
+ return Constant::getNullValue(C1->getType());
+ // Fallthrough
case Instruction::Add:
case Instruction::Sub:
- case Instruction::Xor:
return UndefValue::get(C1->getType());
case Instruction::Mul:
case Instruction::And:
diff --git a/test/CodeGen/X86/xor-undef.ll b/test/CodeGen/X86/xor-undef.ll
new file mode 100644
index 0000000..0e60d4e
--- /dev/null
+++ b/test/CodeGen/X86/xor-undef.ll
@@ -0,0 +1,11 @@
+; RUN: llvm-as < %s | llc -march=x86 -mattr=+sse2 | grep xor | count 2
+
+define <4 x i32> @t1() {
+ %tmp = xor <4 x i32> undef, undef
+ ret <4 x i32> %tmp
+}
+
+define i32 @t2() {
+ %tmp = xor i32 undef, undef
+ ret i32 %tmp
+}