Fix the "test" optimization to recognize "dec" as an add of
negative one, as subtracts of immediates are canonicalized
to adds.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66180 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index d56e672..33eee7a 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -5382,13 +5382,19 @@
UE = Op.getNode()->use_end(); UI != UE; ++UI)
if (UI->getOpcode() == ISD::STORE)
goto default_case;
- // An add of one will be selected as an INC.
if (ConstantSDNode *C =
- dyn_cast<ConstantSDNode>(Op.getNode()->getOperand(1)))
+ dyn_cast<ConstantSDNode>(Op.getNode()->getOperand(1))) {
+ // An add of one will be selected as an INC.
if (C->getAPIntValue() == 1) {
Opcode = X86ISD::INC;
break;
}
+ // An add of negative one (subtract of one) will be selected as a DEC.
+ if (C->getAPIntValue().isAllOnesValue()) {
+ Opcode = X86ISD::DEC;
+ break;
+ }
+ }
// Otherwise use a regular EFLAGS-setting add.
Opcode = X86ISD::ADD;
break;
@@ -5399,13 +5405,6 @@
UE = Op.getNode()->use_end(); UI != UE; ++UI)
if (UI->getOpcode() == ISD::STORE)
goto default_case;
- // A subtract of one will be selected as a DEC.
- if (ConstantSDNode *C =
- dyn_cast<ConstantSDNode>(Op.getNode()->getOperand(1)))
- if (C->getAPIntValue() == 1) {
- Opcode = X86ISD::DEC;
- break;
- }
// Otherwise use a regular EFLAGS-setting sub.
Opcode = X86ISD::SUB;
break;