From eb1ff70fc5fc166fa67dc1cfd5854fc6f51e0b17 Mon Sep 17 00:00:00 2001
From: Pawe Bylica <chfast@gmail.com>
Date: Fri, 25 Feb 2022 14:17:42 +0100
Subject: [PATCH] [X86] Combine ADC(ADD(X,Y),0,Carry) -> ADC(X,Y,Carry)

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D120435
---
 llvm/lib/Target/X86/X86ISelLowering.cpp |  7 +++++++
 llvm/test/CodeGen/X86/addcarry.ll       | 12 ++++--------
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index e46c4ec..1253e5a 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -52150,6 +52150,13 @@ static SDValue combineADC(SDNode *N, SelectionDAG &DAG,
     return DAG.getNode(X86ISD::ADC, SDLoc(N), VTs, LHS, RHS, Flags);
   }
 
+  // Fold ADC(ADD(X,Y),0,Carry) -> ADC(X,Y,Carry)
+  // iff the flag result is dead.
+  if (LHS.getOpcode() == ISD::ADD && isNullConstant(RHS) &&
+      !N->hasAnyUseOfValue(1))
+    return DAG.getNode(X86ISD::ADC, SDLoc(N), N->getVTList(), LHS.getOperand(0),
+                       LHS.getOperand(1), CarryIn);
+
   return SDValue();
 }
 
diff --git a/llvm/test/CodeGen/X86/addcarry.ll b/llvm/test/CodeGen/X86/addcarry.ll
index 3d99661..74ccb7e 100644
--- a/llvm/test/CodeGen/X86/addcarry.ll
+++ b/llvm/test/CodeGen/X86/addcarry.ll
@@ -1366,11 +1366,9 @@ define void @add_U256_without_i128_or_recursive(%uint256* sret(%uint256) %0, %ui
 define i32 @addcarry_ult(i32 %a, i32 %b, i32 %x, i32 %y) {
 ; CHECK-LABEL: addcarry_ult:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    # kill: def $esi killed $esi def $rsi
-; CHECK-NEXT:    # kill: def $edi killed $edi def $rdi
-; CHECK-NEXT:    leal (%rdi,%rsi), %eax
+; CHECK-NEXT:    movl %edi, %eax
 ; CHECK-NEXT:    cmpl %ecx, %edx
-; CHECK-NEXT:    adcl $0, %eax
+; CHECK-NEXT:    adcl %esi, %eax
 ; CHECK-NEXT:    retq
   %s = add i32 %a, %b
   %k = icmp ult i32 %x, %y
@@ -1382,11 +1380,9 @@ define i32 @addcarry_ult(i32 %a, i32 %b, i32 %x, i32 %y) {
 define i32 @addcarry_ugt(i32 %a, i32 %b, i32 %x, i32 %y) {
 ; CHECK-LABEL: addcarry_ugt:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    # kill: def $esi killed $esi def $rsi
-; CHECK-NEXT:    # kill: def $edi killed $edi def $rdi
-; CHECK-NEXT:    leal (%rdi,%rsi), %eax
+; CHECK-NEXT:    movl %edi, %eax
 ; CHECK-NEXT:    cmpl %edx, %ecx
-; CHECK-NEXT:    adcl $0, %eax
+; CHECK-NEXT:    adcl %esi, %eax
 ; CHECK-NEXT:    retq
   %s = add i32 %a, %b
   %k = icmp ugt i32 %x, %y
-- 
2.7.4