[PATCH] D29528: [DAGCombiner] Push truncate through adde when the carry isn't used.

[Amaury SECHET via Phabricator via llvm-commits]

deadalnix updated this revision to Diff 87232.
deadalnix added a comment.

Rebase, clang-format


https://reviews.llvm.org/D29528

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  test/CodeGen/X86/adde-carry.ll


Index: test/CodeGen/X86/adde-carry.ll
===================================================================
--- test/CodeGen/X86/adde-carry.ll
+++ test/CodeGen/X86/adde-carry.ll
@@ -28,8 +28,7 @@
 ; CHECK-LABEL: b:
 ; CHECK:       # BB#0: # %entry
 ; CHECK-NEXT:    addq %rdx, %rsi
-; CHECK-NEXT:    sbbq %rax, %rax
-; CHECK-NEXT:    subl %eax, %ecx
+; CHECK-NEXT:    adcl $0, %ecx
 ; CHECK-NEXT:    movl %ecx, (%rdi)
 ; CHECK-NEXT:    retq
 entry:
@@ -48,8 +47,7 @@
 ; CHECK-LABEL: c:
 ; CHECK:       # BB#0: # %entry
 ; CHECK-NEXT:    addq %rdx, %rsi
-; CHECK-NEXT:    sbbq %rax, %rax
-; CHECK-NEXT:    subl %eax, %ecx
+; CHECK-NEXT:    adcw $0, %cx
 ; CHECK-NEXT:    movw %cx, (%rdi)
 ; CHECK-NEXT:    retq
 entry:
@@ -68,8 +66,7 @@
 ; CHECK-LABEL: d:
 ; CHECK:       # BB#0: # %entry
 ; CHECK-NEXT:    addq %rdx, %rsi
-; CHECK-NEXT:    sbbq %rax, %rax
-; CHECK-NEXT:    subl %eax, %ecx
+; CHECK-NEXT:    adcb $0, %cl
 ; CHECK-NEXT:    movb %cl, (%rdi)
 ; CHECK-NEXT:    retq
 entry:
@@ -164,9 +161,8 @@
 ; CHECK-NEXT:    adcq $0, %rdx
 ; CHECK-NEXT:    movq %rax, (%rdi)
 ; CHECK-NEXT:    addq 8(%rdi), %rdx
-; CHECK-NEXT:    sbbq %rax, %rax
 ; CHECK-NEXT:    movq %rdx, 8(%rdi)
-; CHECK-NEXT:    subl %eax, 16(%rdi)
+; CHECK-NEXT:    adcl $0, 16(%rdi)
 ; CHECK-NEXT:    retq
 entry:
   %0 = zext i64 %arg.a to i128
Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7869,6 +7869,18 @@
       SimplifyDemandedBits(SDValue(N, 0)))
     return SDValue(N, 0);
 
+  // (trunc adde(X, Y, Carry)) -> (adde trunc(X), trunc(Y), Carry)
+  // When the adde's carry is not used.
+  if (N0.getOpcode() == ISD::ADDE && N0.hasOneUse() &&
+      !N0.getNode()->hasAnyUseOfValue(1) &&
+      TLI.isOperationLegalOrCustom(ISD::ADDE, VT)) {
+    SDLoc SL(N);
+    auto X = DAG.getNode(ISD::TRUNCATE, SL, VT, N0.getOperand(0));
+    auto Y = DAG.getNode(ISD::TRUNCATE, SL, VT, N0.getOperand(1));
+    return DAG.getNode(ISD::ADDE, SL, DAG.getVTList(VT, MVT::Glue),
+                       X, Y, N0.getOperand(2));
+  }
+
   return SDValue();
 }
 


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