[PATCH] D141363: [DAGCombiner] Fix issue with rot chain pattern

[chenglin.bi via Phabricator via llvm-commits]

bcl5980 updated this revision to Diff 487842.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D141363/new/

https://reviews.llvm.org/D141363

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/AArch64/rotate.ll


Index: llvm/test/CodeGen/AArch64/rotate.ll
===================================================================
--- llvm/test/CodeGen/AArch64/rotate.ll
+++ llvm/test/CodeGen/AArch64/rotate.ll
@@ -18,14 +18,13 @@
   ret <2 x i64> %4
 }
 
-;; FIXME: This causes miscompile because rot combine
+;; This causes miscompile because rot combine
 ;; doesn't handle negative shift well.
 define i5 @pr59898(i5 %x) {
 ; CHECK-LABEL: pr59898:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    lsr w8, w0, #4
-; CHECK-NEXT:    bfi w8, w0, #1, #31
-; CHECK-NEXT:    mov w0, w8
+; CHECK-NEXT:    ubfx w8, w0, #1, #4
+; CHECK-NEXT:    orr w0, w8, w0, lsl #4
 ; CHECK-NEXT:    ret
   %r1 = call i5 @llvm.fshr.i5(i5 %x, i5 %x, i5 3)
   %r2 = call i5 @llvm.fshl.i5(i5 %r1, i5 %r1, i5 2)
Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -9057,7 +9057,7 @@
   unsigned NextOp = N0.getOpcode();
 
   // fold (rot* (rot* x, c2), c1)
-  //   -> (rot* x, ((c1 % bitsize) +- (c2 % bitsize)) % bitsize)
+  //   -> (rot* x, ((c1 % bitsize) +- (c2 % bitsize) + bitsize) % bitsize)
   if (NextOp == ISD::ROTL || NextOp == ISD::ROTR) {
     SDNode *C1 = DAG.isConstantIntBuildVectorOrConstantInt(N1);
     SDNode *C2 = DAG.isConstantIntBuildVectorOrConstantInt(N0.getOperand(1));
@@ -9073,6 +9073,8 @@
       if (Norm1 && Norm2)
         if (SDValue CombinedShift = DAG.FoldConstantArithmetic(
                 CombineOp, dl, ShiftVT, {Norm1, Norm2})) {
+          CombinedShift = DAG.FoldConstantArithmetic(ISD::ADD, dl, ShiftVT,
+                                                     {CombinedShift, BitsizeC});
           SDValue CombinedShiftNorm = DAG.FoldConstantArithmetic(
               ISD::UREM, dl, ShiftVT, {CombinedShift, BitsizeC});
           return DAG.getNode(N->getOpcode(), dl, VT, N0->getOperand(0),


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D141363.487842.patch
Type: text/x-patch
Size: 1958 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20230110/ec65443d/attachment.bin>