[llvm] 7c66aad - [DAG] Fold (X & Y) != 0 --> zextOrTrunc(X & Y) iff everything but LSB is known zero (PR51312)

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2022-01-23T16:20:42Z
New Revision: 7c66aaddb128dc0f342830c1efaeb7a278bfc48c

URL: https://github.com/llvm/llvm-project/commit/7c66aaddb128dc0f342830c1efaeb7a278bfc48c
DIFF: https://github.com/llvm/llvm-project/commit/7c66aaddb128dc0f342830c1efaeb7a278bfc48c.diff

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

Fixes parity codegen issue where we know all but the lowest bit is zero, we can replace the ICMPNE with 0 comparison with a ext/trunc

Differential Revision: https://reviews.llvm.org/D117983

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 3b53a5b8b7532..269c332ae28a1 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -3254,17 +3254,29 @@ bool TargetLowering::isExtendedTrueVal(const ConstantSDNode *N, EVT VT,
 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 (Cond == ISD::SETNE && isNullConstant(N1) &&
+      (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.getBoolExtOrTrunc(N0, DL, VT, OpVT);
+  }
+
+  // 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 @@ SDValue TargetLowering::foldSetCCWithAnd(EVT VT, SDValue N0, SDValue N1,
     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.

diff  --git a/llvm/test/CodeGen/X86/parity-vec.ll b/llvm/test/CodeGen/X86/parity-vec.ll
index 60d9d4be68e79..ed64bb5eddf49 100644
--- a/llvm/test/CodeGen/X86/parity-vec.ll
+++ b/llvm/test/CodeGen/X86/parity-vec.ll
@@ -36,8 +36,8 @@ define i1 @canonical_parity(<16 x i1> %x) {
 ; 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)