[PATCH] D130251: [DAGCombine] Mask don't have to be (EltSize - 1) exactly when combining rotation

[Wang Pengcheng via Phabricator via llvm-commits]

pcwang-thead updated this revision to Diff 446458.
pcwang-thead added a comment.

Address comment.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D130251/new/

https://reviews.llvm.org/D130251

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/RISCV/rotl-rotr.ll


Index: llvm/test/CodeGen/RISCV/rotl-rotr.ll
===================================================================
--- llvm/test/CodeGen/RISCV/rotl-rotr.ll
+++ llvm/test/CodeGen/RISCV/rotl-rotr.ll
@@ -341,18 +341,12 @@
 ;
 ; RV32ZBB-LABEL: rotl_32_mask_1:
 ; RV32ZBB:       # %bb.0:
-; RV32ZBB-NEXT:    sll a2, a0, a1
-; RV32ZBB-NEXT:    neg a1, a1
-; RV32ZBB-NEXT:    srl a0, a0, a1
-; RV32ZBB-NEXT:    or a0, a2, a0
+; RV32ZBB-NEXT:    rol a0, a0, a1
 ; RV32ZBB-NEXT:    ret
 ;
 ; RV64ZBB-LABEL: rotl_32_mask_1:
 ; RV64ZBB:       # %bb.0:
-; RV64ZBB-NEXT:    sllw a2, a0, a1
-; RV64ZBB-NEXT:    negw a1, a1
-; RV64ZBB-NEXT:    srlw a0, a0, a1
-; RV64ZBB-NEXT:    or a0, a2, a0
+; RV64ZBB-NEXT:    rolw a0, a0, a1
 ; RV64ZBB-NEXT:    ret
   %a = and i32 %y, 63
   %b = shl i32 %x, %a
@@ -416,18 +410,12 @@
 ;
 ; RV32ZBB-LABEL: rotr_32_mask_1:
 ; RV32ZBB:       # %bb.0:
-; RV32ZBB-NEXT:    srl a2, a0, a1
-; RV32ZBB-NEXT:    neg a1, a1
-; RV32ZBB-NEXT:    sll a0, a0, a1
-; RV32ZBB-NEXT:    or a0, a2, a0
+; RV32ZBB-NEXT:    ror a0, a0, a1
 ; RV32ZBB-NEXT:    ret
 ;
 ; RV64ZBB-LABEL: rotr_32_mask_1:
 ; RV64ZBB:       # %bb.0:
-; RV64ZBB-NEXT:    srlw a2, a0, a1
-; RV64ZBB-NEXT:    negw a1, a1
-; RV64ZBB-NEXT:    sllw a0, a0, a1
-; RV64ZBB-NEXT:    or a0, a2, a0
+; RV64ZBB-NEXT:    rorw a0, a0, a1
 ; RV64ZBB-NEXT:    ret
   %a = and i32 %y, 63
   %b = lshr i32 %x, %a
Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7277,6 +7277,7 @@
 // Otherwise if matching a general funnel shift, it should be clear.
 static bool matchRotateSub(SDValue Pos, SDValue Neg, unsigned EltSize,
                            SelectionDAG &DAG, bool IsRotate) {
+  const auto &TLI = DAG.getTargetLoweringInfo();
   // If EltSize is a power of 2 then:
   //
   //  (a) (Pos == 0 ? 0 : EltSize - Pos) == (EltSize - Pos) & (EltSize - 1)
@@ -7312,15 +7313,13 @@
   // NOTE: We can only do this when matching an AND and not a general
   // funnel shift.
   unsigned MaskLoBits = 0;
-  if (IsRotate && Neg.getOpcode() == ISD::AND && isPowerOf2_64(EltSize)) {
-    if (ConstantSDNode *NegC = isConstOrConstSplat(Neg.getOperand(1))) {
-      KnownBits Known = DAG.computeKnownBits(Neg.getOperand(0));
-      unsigned Bits = Log2_64(EltSize);
-      if (NegC->getAPIntValue().getActiveBits() <= Bits &&
-          ((NegC->getAPIntValue() | Known.Zero).countTrailingOnes() >= Bits)) {
-        Neg = Neg.getOperand(0);
-        MaskLoBits = Bits;
-      }
+  if (IsRotate && isPowerOf2_64(EltSize)) {
+    unsigned Bits = Log2_64(EltSize);
+    APInt DemandedBits = APInt::getLowBitsSet(EltSize, Bits);
+    if (SDValue Inner =
+            TLI.SimplifyMultipleUseDemandedBits(Neg, DemandedBits, DAG)) {
+      Neg = Inner;
+      MaskLoBits = Bits;
     }
   }
 
@@ -7334,13 +7333,11 @@
 
   // On the RHS of [A], if Pos is Pos' & (EltSize - 1), just replace Pos with
   // Pos'.  The truncation is redundant for the purpose of the equality.
-  if (MaskLoBits && Pos.getOpcode() == ISD::AND) {
-    if (ConstantSDNode *PosC = isConstOrConstSplat(Pos.getOperand(1))) {
-      KnownBits Known = DAG.computeKnownBits(Pos.getOperand(0));
-      if (PosC->getAPIntValue().getActiveBits() <= MaskLoBits &&
-          ((PosC->getAPIntValue() | Known.Zero).countTrailingOnes() >=
-           MaskLoBits))
-        Pos = Pos.getOperand(0);
+  if (MaskLoBits) {
+    APInt DemandedBits = APInt::getLowBitsSet(EltSize, MaskLoBits);
+    if (SDValue Inner =
+            TLI.SimplifyMultipleUseDemandedBits(Pos, DemandedBits, DAG)) {
+      Pos = Inner;
     }
   }
 


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