From: Craig Topper <craig.topper@intel.com>
Date: Thu, 4 Jul 2019 18:18:46 +0000 (+0000)
Subject: [DAGCombiner] Don't combine (addcarry (uaddo X, Y), 0, Carry) -> (addcarry X, Y,... 
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=394ab2ed6fb573a6760c29bf889736dfc07c1a82;p=llvm

[DAGCombiner] Don't combine (addcarry (uaddo X, Y), 0, Carry) -> (addcarry X, Y, Carry) if the Carry comes from the uaddo.

Summary:
The uaddo won't be removed and the addcarry will still be
dependent on the uaddo. So we'll just increase the use count
of X and Y and potentially require a COPY.

Reviewers: spatel, RKSimon, deadalnix

Reviewed By: RKSimon

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64190

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@365149 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index b0e017571f6..c00f89267fb 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2966,8 +2966,11 @@ SDValue DAGCombiner::visitADDCARRYLike(SDValue N0, SDValue N1, SDValue CarryIn,
                                        SDNode *N) {
   // Iff the flag result is dead:
   // (addcarry (add|uaddo X, Y), 0, Carry) -> (addcarry X, Y, Carry)
+  // Don't do this if the Carry comes from the uaddo. It won't remove the uaddo
+  // or the dependency between the instructions.
   if ((N0.getOpcode() == ISD::ADD ||
-       (N0.getOpcode() == ISD::UADDO && N0.getResNo() == 0)) &&
+       (N0.getOpcode() == ISD::UADDO && N0.getResNo() == 0 &&
+        N0.getValue(1) != CarryIn)) &&
       isNullConstant(N1) && !N->hasAnyUseOfValue(1))
     return DAG.getNode(ISD::ADDCARRY, SDLoc(N), N->getVTList(),
                        N0.getOperand(0), N0.getOperand(1), CarryIn);
diff --git a/test/CodeGen/X86/add-of-carry.ll b/test/CodeGen/X86/add-of-carry.ll
index 1149ae57552..9bb50de25b2 100644
--- a/test/CodeGen/X86/add-of-carry.ll
+++ b/test/CodeGen/X86/add-of-carry.ll
@@ -9,11 +9,9 @@
 define i32 @test1(i32 %sum, i32 %x) nounwind readnone ssp {
 ; CHECK-LABEL: test1:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %ecx
 ; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; CHECK-NEXT:    movl %eax, %edx
-; CHECK-NEXT:    addl %ecx, %edx
-; CHECK-NEXT:    adcl %ecx, %eax
+; CHECK-NEXT:    addl {{[0-9]+}}(%esp), %eax
+; CHECK-NEXT:    adcl $0, %eax
 ; CHECK-NEXT:    retl
   %add4 = add i32 %x, %sum
   %cmp = icmp ult i32 %add4, %x