now that addc/adde are gone, "ADDC" in the X86 backend uses EFLAGS results,

the same as setcc.  Optimize ADDC(0,0,FLAGS) -> SET_CARRY(FLAGS).  This is
a step towards finishing off PR5443.  In the testcase in that bug we now  get:

	movq	%rdi, %rax
	addq	%rsi, %rax
	sbbq	%rcx, %rcx
	testb	$1, %cl
	setne	%dl
	ret

instead of:

	movq	%rdi, %rax
	addq	%rsi, %rax
	movl	$0, %ecx
	adcq	$0, %rcx
	testq	%rcx, %rcx
	setne	%dl
	ret



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122219 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 27 insertions, 0 deletions

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 05cd3af..55c83a5 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -11493,6 +11493,32 @@ static SDValue PerformSETCCCombine(SDNode *N, SelectionDAG &DAG) {
   
   return SDValue();
 }
+          
+// Optimize RES, EFLAGS = X86ISD::ADC LHS, RHS, EFLAGS
+static SDValue PerformADCCombine(SDNode *N, SelectionDAG &DAG,
+                                 X86TargetLowering::DAGCombinerInfo &DCI) {
+  // If the LHS and RHS of the ADC node are zero, then it can't overflow and
+  // the result is either zero or one (depending on the input carry bit).
+  // Strength reduce this down to a "set on carry" aka SETCC_CARRY&1.
+  if (X86::isZeroNode(N->getOperand(0)) &&
+      X86::isZeroNode(N->getOperand(1)) &&
+      // We don't have a good way to replace an EFLAGS use, so only do this when
+      // dead right now.
+      SDValue(N, 1).use_empty()) {
+    DebugLoc DL = N->getDebugLoc();
+    EVT VT = N->getValueType(0);
+    SDValue CarryOut = DAG.getConstant(0, N->getValueType(1));
+    SDValue Res1 = DAG.getNode(ISD::AND, DL, VT,
+                               DAG.getNode(X86ISD::SETCC_CARRY, DL, VT,
+                                           DAG.getConstant(X86::COND_B,MVT::i8),
+                                           N->getOperand(2)),
+                               DAG.getConstant(1, VT));
+    return DCI.CombineTo(N, Res1, CarryOut);
+  }
+
+  return SDValue();
+}
+
 
 SDValue X86TargetLowering::PerformDAGCombine(SDNode *N,
                                              DAGCombinerInfo &DCI) const {
@@ -11503,6 +11529,7 @@ SDValue X86TargetLowering::PerformDAGCombine(SDNode *N,
     return PerformEXTRACT_VECTOR_ELTCombine(N, DAG, *this);
   case ISD::SELECT:         return PerformSELECTCombine(N, DAG, Subtarget);
   case X86ISD::CMOV:        return PerformCMOVCombine(N, DAG, DCI);
+  case X86ISD::ADC:         return PerformADCCombine(N, DAG, DCI);
   case ISD::MUL:            return PerformMulCombine(N, DAG, DCI);
   case ISD::SHL:
   case ISD::SRA: