[PATCH] D122551: [AArch64] Enhance last active true vector combine

[Allen zhong via Phabricator via llvm-commits]

Allen created this revision.
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Last active extracting will output LASTB + WHILELS, and the WHILELS itself
is a flag-setting operation, so perform it unconditionally.


https://reviews.llvm.org/D122551

Files:
  llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
  llvm/test/CodeGen/AArch64/sve-extract-element.ll


Index: llvm/test/CodeGen/AArch64/sve-extract-element.ll
===================================================================
--- llvm/test/CodeGen/AArch64/sve-extract-element.ll
+++ llvm/test/CodeGen/AArch64/sve-extract-element.ll
@@ -504,12 +504,9 @@
 define i1 @test_last_8xi1(<vscale x 8 x i1> %a) #0 {
 ; CHECK-LABEL: test_last_8xi1:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    cnth x8
-; CHECK-NEXT:    mov z0.h, p0/z, #1 // =0x1
-; CHECK-NEXT:    sub x8, x8, #1
-; CHECK-NEXT:    whilels p0.h, xzr, x8
-; CHECK-NEXT:    lastb w8, p0, z0.h
-; CHECK-NEXT:    and w0, w8, #0x1
+; CHECK-NEXT:    ptrue p1.h
+; CHECK-NEXT:    ptest p1, p0.b
+; CHECK-NEXT:    cset w0, lo
 ; CHECK-NEXT:    ret
   %vscale = call i64 @llvm.vscale.i64()
   %shl = shl nuw nsw i64 %vscale, 3
Index: llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
===================================================================
--- llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -14422,8 +14422,8 @@
   if (!Subtarget->hasSVE() || DCI.isBeforeLegalize())
     return SDValue();
 
-  SDValue SetCC = N->getOperand(0);
-  EVT OpVT = SetCC.getValueType();
+  SDValue N0 = N->getOperand(0);
+  EVT OpVT = N0.getValueType();
 
   if (!OpVT.isScalableVector() || OpVT.getVectorElementType() != MVT::i1)
     return SDValue();
@@ -14441,16 +14441,15 @@
   if (VS.getConstantOperandVal(0) != NumEls)
     return SDValue();
 
-  // Restricted the DAG combine to only cases where we're extracting from a
-  // flag-setting operation
-  auto *CI = dyn_cast<ConstantSDNode>(Idx.getOperand(1));
-  if (!CI || !CI->isAllOnes() || SetCC.getOpcode() != ISD::SETCC)
+  // Last active extracting will output LASTB + WHILELS, and the WHILELS itself
+  // is a flag-setting operation, so perform it unconditionally.
+  if (!isAllOnesConstant(Idx.getOperand(1)))
     return SDValue();
 
   // Extracts of lane EC-1 for SVE can be expressed as PTEST(Op, LAST) ? 1 : 0
   SelectionDAG &DAG = DCI.DAG;
   SDValue Pg = getPTrue(DAG, SDLoc(N), OpVT, AArch64SVEPredPattern::all);
-  return getPTest(DAG, N->getValueType(0), Pg, SetCC, AArch64CC::LAST_ACTIVE);
+  return getPTest(DAG, N->getValueType(0), Pg, N0, AArch64CC::LAST_ACTIVE);
 }
 
 static SDValue


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