[PATCH] D74032: [DAGCombine][ARM] Combine pattern for REV16

[Sjoerd Meijer via Phabricator via llvm-commits]

SjoerdMeijer updated this revision to Diff 242565.
SjoerdMeijer added a comment.

Ah yes, thanks for the tip.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D74032/new/

https://reviews.llvm.org/D74032

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/Thumb2/thumb2-rev16.ll


Index: llvm/test/CodeGen/Thumb2/thumb2-rev16.ll
===================================================================
--- llvm/test/CodeGen/Thumb2/thumb2-rev16.ll
+++ llvm/test/CodeGen/Thumb2/thumb2-rev16.ll
@@ -6,11 +6,7 @@
 define i32 @f1(i32 %a) {
 ; CHECK-LABEL: f1:
 ; CHECK:       @ %bb.0:
-; CHECK-NEXT:    mov.w r1, #16711935
-; CHECK-NEXT:    mov.w r2, #-16711936
-; CHECK-NEXT:    and.w r1, r1, r0, lsr #8
-; CHECK-NEXT:    and.w r0, r2, r0, lsl #8
-; CHECK-NEXT:    add r0, r1
+; CHECK-NEXT:    rev16 r0, r0
 ; CHECK-NEXT:    bx lr
     %l8 = shl i32 %a, 8
     %r8 = lshr i32 %a, 8
Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -5647,6 +5647,43 @@
   return false;
 }
 
+// Match this pattern:
+//   (or (and (shl (A, 8)), 0xff00ff00), (and (srl (A, 8)), 0x00ff00ff))
+// And rewrite this to:
+//   (rotr (bswap A), 16)
+static SDValue MatchBSwapHWordOrAndAnd(const TargetLowering &TLI,
+                                       SelectionDAG &DAG, SDNode *N, SDValue N0,
+                                       SDValue N1, EVT VT, EVT ShiftAmountTy) {
+  if (!TLI.isOperationLegalOrCustom(ISD::ROTR, VT))
+    return SDValue();
+  if (N0.getOpcode() != ISD::AND || N1.getOpcode() != ISD::AND)
+    return SDValue();
+  ConstantSDNode *Mask1 = dyn_cast<ConstantSDNode>(N0.getOperand(1));
+  ConstantSDNode *Mask2 = dyn_cast<ConstantSDNode>(N1.getOperand(1));
+  if (!Mask1 || !Mask2)
+    return SDValue();
+  if (Mask1->getAPIntValue() != 0xff00ff00 ||
+      Mask2->getAPIntValue() != 0x00ff00ff)
+    return SDValue();
+  SDValue Shift1 = N0.getOperand(0);
+  SDValue Shift2 = N1.getOperand(0);
+  if (Shift1.getOpcode() != ISD::SHL || Shift2.getOpcode() != ISD::SRL)
+    return SDValue();
+  ConstantSDNode *Const1 = dyn_cast<ConstantSDNode>(Shift1.getOperand(1));
+  ConstantSDNode *Const2 = dyn_cast<ConstantSDNode>(Shift2.getOperand(1));
+  if (!Const1 || !Const2)
+    return SDValue();
+  if (Const1->getAPIntValue() != 8 || Const2->getAPIntValue() != 8)
+    return SDValue();
+  if (Shift1.getOperand(0) != Shift2.getOperand(0))
+    return SDValue();
+
+  SDLoc DL(N);
+  SDValue BSwap = DAG.getNode(ISD::BSWAP, DL, VT, Shift1.getOperand(0));
+  SDValue ShAmt = DAG.getConstant(16, DL, ShiftAmountTy);
+  return DAG.getNode(ISD::ROTR, DL, VT, BSwap, ShAmt);
+}
+
 /// Match a 32-bit packed halfword bswap. That is
 /// ((x & 0x000000ff) << 8) |
 /// ((x & 0x0000ff00) >> 8) |
@@ -5663,6 +5700,10 @@
   if (!TLI.isOperationLegalOrCustom(ISD::BSWAP, VT))
     return SDValue();
 
+  if (SDValue BSwap = MatchBSwapHWordOrAndAnd(TLI, DAG, N, N0, N1, VT,
+                                              getShiftAmountTy(VT)))
+    return BSwap;
+
   // Look for either
   // (or (bswaphpair), (bswaphpair))
   // (or (or (bswaphpair), (and)), (and))


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