[PATCH] D117983: [DAG] Fold (X & Y) != 0 --> zextOrTrunc(X & Y) iff everything but LSB is known zero (PR51312)

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon updated this revision to Diff 402328.
RKSimon added a comment.

rebase


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D117983/new/

https://reviews.llvm.org/D117983

Files:
  llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
  llvm/test/CodeGen/X86/parity-vec.ll


Index: llvm/test/CodeGen/X86/parity-vec.ll
===================================================================
--- llvm/test/CodeGen/X86/parity-vec.ll
+++ llvm/test/CodeGen/X86/parity-vec.ll
@@ -36,8 +36,8 @@
 ; POPCNT-NEXT:    psllw $7, %xmm0
 ; POPCNT-NEXT:    pmovmskb %xmm0, %eax
 ; POPCNT-NEXT:    popcntl %eax, %eax
-; POPCNT-NEXT:    testb $1, %al
-; POPCNT-NEXT:    setne %al
+; POPCNT-NEXT:    andl $1, %eax
+; POPCNT-NEXT:    # kill: def $al killed $al killed $eax
 ; POPCNT-NEXT:    retq
   %i1 = bitcast <16 x i1> %x to i16
   %i2 = call i16 @llvm.ctpop.i16(i16 %i1)
Index: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -3254,17 +3254,29 @@
 SDValue TargetLowering::foldSetCCWithAnd(EVT VT, SDValue N0, SDValue N1,
                                          ISD::CondCode Cond, const SDLoc &DL,
                                          DAGCombinerInfo &DCI) const {
-  // Match these patterns in any of their permutations:
-  // (X & Y) == Y
-  // (X & Y) != Y
   if (N1.getOpcode() == ISD::AND && N0.getOpcode() != ISD::AND)
     std::swap(N0, N1);
 
+  SelectionDAG &DAG = DCI.DAG;
   EVT OpVT = N0.getValueType();
   if (N0.getOpcode() != ISD::AND || !OpVT.isInteger() ||
       (Cond != ISD::SETEQ && Cond != ISD::SETNE))
     return SDValue();
 
+  // (X & Y) != 0 --> zextOrTrunc(X & Y)
+  // iff everything but LSB is known zero:
+  if (isNullConstant(N1) && Cond == ISD::SETNE &&
+      (getBooleanContents(VT) == TargetLowering::UndefinedBooleanContent ||
+       getBooleanContents(VT) == TargetLowering::ZeroOrOneBooleanContent)) {
+    unsigned NumEltBits = OpVT.getScalarSizeInBits();
+    APInt UpperBits = APInt::getHighBitsSet(NumEltBits, NumEltBits - 1);
+    if (DAG.MaskedValueIsZero(N0, UpperBits))
+      return DAG.getZExtOrTrunc(N0, DL, VT);
+  }
+
+  // Match these patterns in any of their permutations:
+  // (X & Y) == Y
+  // (X & Y) != Y
   SDValue X, Y;
   if (N0.getOperand(0) == N1) {
     X = N0.getOperand(1);
@@ -3276,7 +3288,6 @@
     return SDValue();
   }
 
-  SelectionDAG &DAG = DCI.DAG;
   SDValue Zero = DAG.getConstant(0, DL, OpVT);
   if (DAG.isKnownToBeAPowerOfTwo(Y)) {
     // Simplify X & Y == Y to X & Y != 0 if Y has exactly one bit set.


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