From 0727e2b90c7b11d5c6be55919c443628d8e2bc6e Mon Sep 17 00:00:00 2001
From: Roman Lebedev <lebedev.ri@gmail.com>
Date: Fri, 3 Jan 2020 16:14:29 +0300
Subject: [DAGCombiner][X86][AArch64] Generalize `A-(A&B)`->`A&(~B)` fold
 (PR44448)

The fold 'A - (A & (B - 1))' -> 'A & (0 - B)'
added in 8dab0a4a7d691f2704f1079538e0ef29548db159
is too specific. It should/can just be 'A - (A & B)' -> 'A & (~B)'

Even if we don't manage to fold `~` into B,
we have likely formed `ANDN` node.
Also, this way there's less similar-but-duplicate folds.

Name: X - (X & Y)  ->  X & (~Y)
%o = and i32 %X, %Y
%r = sub i32 %X, %o
  =>
%n = xor i32 %Y, -1
%r = and i32 %X, %n

https://rise4fun.com/Alive/kOUl

See
  https://bugs.llvm.org/show_bug.cgi?id=44448
  https://reviews.llvm.org/D71499
---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 29 +++++++++------------------
 1 file changed, 9 insertions(+), 20 deletions(-)

(limited to 'llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp')

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 5a8b4d456d9..3bfea38932f 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3104,31 +3104,20 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
                        DAG.getNode(ISD::SUB, DL, VT, N1.getOperand(1),
                                    N1.getOperand(0)));
 
-  // A - (A & (B - 1))  ->  A & (~(B - 1))  ->  A & (0 - B)
-  if (N1.getOpcode() == ISD::AND && N1.hasOneUse()) {
+  // A - (A & B)  ->  A & (~B)
+  if (N1.getOpcode() == ISD::AND) {
     SDValue A = N1.getOperand(0);
-    SDValue BDec = N1.getOperand(1);
+    SDValue B = N1.getOperand(1);
     if (A != N0)
-      std::swap(A, BDec);
-    if (A == N0 && BDec.getOpcode() == ISD::ADD &&
-        isAllOnesOrAllOnesSplat(BDec->getOperand(1))) {
-      SDValue B = BDec.getOperand(0);
-      SDValue NegB =
-          DAG.getNode(ISD::SUB, DL, VT, DAG.getConstant(0, DL, VT), B);
-      return DAG.getNode(ISD::AND, DL, VT, A, NegB);
+      std::swap(A, B);
+    if (A == N0 &&
+        (N1.hasOneUse() || isConstantOrConstantVector(B, /*NoOpaques=*/true))) {
+      SDValue InvB =
+          DAG.getNode(ISD::XOR, DL, VT, B, DAG.getAllOnesConstant(DL, VT));
+      return DAG.getNode(ISD::AND, DL, VT, A, InvB);
     }
   }
 
-  // A - (A & C) -> A & (~C)
-  if (N1.getOpcode() == ISD::AND && N1.getOperand(0) == N0 &&
-      isConstantOrConstantVector(N1.getOperand(1), /*NoOpaques=*/true)) {
-    SDValue InvC =
-        DAG.FoldConstantArithmetic(ISD::XOR, DL, VT, N1.getOperand(1).getNode(),
-                                   DAG.getAllOnesConstant(DL, VT).getNode());
-    assert(InvC && "Constant folding failed");
-    return DAG.getNode(ISD::AND, DL, VT, N0, InvC);
-  }
-
   // fold (X - (-Y * Z)) -> (X + (Y * Z))
   if (N1.getOpcode() == ISD::MUL && N1.hasOneUse()) {
     if (N1.getOperand(0).getOpcode() == ISD::SUB &&
-- 
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