[DAGCombiner] Do various combine on usubo.

deadalnix · deadalnix · commit 10425de0632a · 2017-03-09T19:28:00.000Z
Summary: This essentially does the same transform as for SUBC. Reviewers: jyknight, nemanjai, mkuper, spatel, RKSimon, zvi, bkramer Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D30437 llvm-svn: 297404
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -236,6 +236,7 @@ namespace {
     SDValue visitSUB(SDNode *N);
     SDValue visitADDC(SDNode *N);
     SDValue visitSUBC(SDNode *N);
+    SDValue visitUSUBO(SDNode *N);
     SDValue visitADDE(SDNode *N);
     SDValue visitSUBE(SDNode *N);
     SDValue visitMUL(SDNode *N);
@@ -1400,6 +1401,7 @@ SDValue DAGCombiner::visit(SDNode *N) {
   case ISD::SUB:                return visitSUB(N);
   case ISD::ADDC:               return visitADDC(N);
   case ISD::SUBC:               return visitSUBC(N);
+  case ISD::USUBO:              return visitUSUBO(N);
   case ISD::ADDE:               return visitADDE(N);
   case ISD::SUBE:               return visitSUBE(N);
   case ISD::MUL:                return visitMUL(N);
@@ -2133,6 +2135,38 @@ SDValue DAGCombiner::visitSUBC(SDNode *N) {
   return SDValue();
 }
 
+SDValue DAGCombiner::visitUSUBO(SDNode *N) {
+  SDValue N0 = N->getOperand(0);
+  SDValue N1 = N->getOperand(1);
+  EVT VT = N0.getValueType();
+  if (VT.isVector())
+    return SDValue();
+
+  EVT CarryVT = N->getValueType(1);
+  SDLoc DL(N);
+
+  // If the flag result is dead, turn this into an SUB.
+  if (!N->hasAnyUseOfValue(1))
+    return CombineTo(N, DAG.getNode(ISD::SUB, DL, VT, N0, N1),
+                     DAG.getUNDEF(CarryVT));
+
+  // fold (usubo x, x) -> 0 + no borrow
+  if (N0 == N1)
+    return CombineTo(N, DAG.getConstant(0, DL, VT),
+                     DAG.getConstant(0, DL, CarryVT));
+
+  // fold (usubo x, 0) -> x + no borrow
+  if (isNullConstant(N1))
+    return CombineTo(N, N0, DAG.getConstant(0, DL, CarryVT));
+
+  // Canonicalize (usubo -1, x) -> ~x, i.e. (xor x, -1) + no borrow
+  if (isAllOnesConstant(N0))
+    return CombineTo(N, DAG.getNode(ISD::XOR, DL, VT, N1, N0),
+                     DAG.getConstant(0, DL, CarryVT));
+
+  return SDValue();
+}
+
 SDValue DAGCombiner::visitSUBE(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
diff --git a/llvm/test/CodeGen/X86/xaluo.ll b/llvm/test/CodeGen/X86/xaluo.ll
@@ -1372,43 +1372,23 @@ define {i64, i1} @uaddoovf(i64 %a, i64 %b) {
 define {i64, i1} @usuboovf(i64 %a, i64 %b) {
 ; SDAG-LABEL: usuboovf:
 ; SDAG:       ## BB#0:
-; SDAG-NEXT:    subq %rdi, %rdi
-; SDAG-NEXT:    sbbb %r8b, %r8b
-; SDAG-NEXT:    movq $-1, %rax
-; SDAG-NEXT:    subq %rsi, %rax
-; SDAG-NEXT:    sbbb %cl, %cl
-; SDAG-NEXT:    subq %rdi, %rax
-; SDAG-NEXT:    sbbb %dl, %dl
-; SDAG-NEXT:    orb %cl, %dl
-; SDAG-NEXT:    orb %r8b, %dl
-; SDAG-NEXT:    andb $1, %dl
+; SDAG-NEXT:    notq %rsi
+; SDAG-NEXT:    xorl %edx, %edx
+; SDAG-NEXT:    movq %rsi, %rax
 ; SDAG-NEXT:    retq
 ;
 ; FAST-LABEL: usuboovf:
 ; FAST:       ## BB#0:
-; FAST-NEXT:    subq %rdi, %rdi
-; FAST-NEXT:    sbbb %r8b, %r8b
-; FAST-NEXT:    movq $-1, %rax
-; FAST-NEXT:    subq %rsi, %rax
-; FAST-NEXT:    sbbb %cl, %cl
-; FAST-NEXT:    subq %rdi, %rax
-; FAST-NEXT:    sbbb %dl, %dl
-; FAST-NEXT:    orb %cl, %dl
-; FAST-NEXT:    orb %r8b, %dl
-; FAST-NEXT:    andb $1, %dl
+; FAST-NEXT:    notq %rsi
+; FAST-NEXT:    xorl %edx, %edx
+; FAST-NEXT:    movq %rsi, %rax
 ; FAST-NEXT:    retq
 ;
 ; KNL-LABEL: usuboovf:
 ; KNL:       ## BB#0:
-; KNL-NEXT:    subq %rdi, %rdi
-; KNL-NEXT:    sbbb %dl, %dl
-; KNL-NEXT:    movq $-1, %rax
-; KNL-NEXT:    subq %rsi, %rax
-; KNL-NEXT:    sbbb %cl, %cl
-; KNL-NEXT:    orb %dl, %cl
-; KNL-NEXT:    subq %rdi, %rax
-; KNL-NEXT:    sbbb %dl, %dl
-; KNL-NEXT:    orb %cl, %dl
+; KNL-NEXT:    notq %rsi
+; KNL-NEXT:    xorl %edx, %edx
+; KNL-NEXT:    movq %rsi, %rax
 ; KNL-NEXT:    retq
   %t0 = call {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %a)
   %v0 = extractvalue {i64, i1} %t0, 0
