[PATCH] D58874: [DAGCombiner] fold (add (add (xor a, -1), b), 1) -> (sub b, a)

[Amaury SECHET via Phabricator via llvm-commits]

deadalnix created this revision.
deadalnix added reviewers: efriedma, spatel, RKSimon, zvi, bkramer.
Herald added a project: LLVM.

This pattern is sometime created after legalization.


Repository:
  rL LLVM

https://reviews.llvm.org/D58874

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  test/CodeGen/X86/add.ll


Index: test/CodeGen/X86/add.ll
===================================================================
--- test/CodeGen/X86/add.ll
+++ test/CodeGen/X86/add.ll
@@ -482,25 +482,19 @@
 ; X32-LABEL: add_to_sub:
 ; X32:       # %bb.0:
 ; X32-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X32-NEXT:    movl {{[0-9]+}}(%esp), %ecx
-; X32-NEXT:    notl %ecx
-; X32-NEXT:    leal 1(%ecx,%eax), %eax
+; X32-NEXT:    subl {{[0-9]+}}(%esp), %eax
 ; X32-NEXT:    retl
 ;
 ; X64-LINUX-LABEL: add_to_sub:
 ; X64-LINUX:       # %bb.0:
-; X64-LINUX-NEXT:    # kill: def $esi killed $esi def $rsi
-; X64-LINUX-NEXT:    # kill: def $edi killed $edi def $rdi
-; X64-LINUX-NEXT:    notl %edi
-; X64-LINUX-NEXT:    leal 1(%rdi,%rsi), %eax
+; X64-LINUX-NEXT:    movl %esi, %eax
+; X64-LINUX-NEXT:    subl %edi, %eax
 ; X64-LINUX-NEXT:    retq
 ;
 ; X64-WIN32-LABEL: add_to_sub:
 ; X64-WIN32:       # %bb.0:
-; X64-WIN32-NEXT:    # kill: def $edx killed $edx def $rdx
-; X64-WIN32-NEXT:    # kill: def $ecx killed $ecx def $rcx
-; X64-WIN32-NEXT:    notl %ecx
-; X64-WIN32-NEXT:    leal 1(%rcx,%rdx), %eax
+; X64-WIN32-NEXT:    movl %edx, %eax
+; X64-WIN32-NEXT:    subl %ecx, %eax
 ; X64-WIN32-NEXT:    retq
   %nota = xor i32 %a, -1
   %add = add i32 %nota, %b
Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2185,10 +2185,30 @@
       DAG.haveNoCommonBitsSet(N0, N1))
     return DAG.getNode(ISD::OR, DL, VT, N0, N1);
 
-  // fold (add (xor a, -1), 1) -> (sub 0, a)
-  if (isBitwiseNot(N0) && isOneOrOneSplat(N1))
-    return DAG.getNode(ISD::SUB, DL, VT, DAG.getConstant(0, DL, VT),
-                       N0.getOperand(0));
+  if (isOneOrOneSplat(N1)) {
+    // fold (add (xor a, -1), 1) -> (sub 0, a)
+    if (isBitwiseNot(N0))
+      return DAG.getNode(ISD::SUB, DL, VT, DAG.getConstant(0, DL, VT),
+                         N0.getOperand(0));
+
+    // fold (add (add (xor a, -1), b), 1) -> (sub b, a)
+    if (N0.getOpcode() == ISD::ADD ||
+        N0.getOpcode() == ISD::UADDO ||
+        N0.getOpcode() == ISD::SADDO) {
+      SDValue A, Xor;
+
+      if (isBitwiseNot(N0.getOperand(0))) {
+        A = N0.getOperand(1);
+        Xor = N0.getOperand(0);
+      } else if (isBitwiseNot(N0.getOperand(1))) {
+        A = N0.getOperand(0);
+        Xor = N0.getOperand(1);
+      }
+
+      if (Xor)
+        return DAG.getNode(ISD::SUB, DL, VT, A, Xor.getOperand(0));
+    }
+  }
 
   if (SDValue Combined = visitADDLike(N0, N1, N))
     return Combined;


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