[clang] [llvm] [DXIL][SPIRV] Lower WaveActiveCountBits intrinsic (PR #113382)

[Greg Roth via llvm-commits]

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@@ -1762,6 +1765,36 @@ bool SPIRVInstructionSelector::selectSign(Register ResVReg,
   return Result;
 }
 
+bool SPIRVInstructionSelector::selectWaveActiveCountBits(
+    Register ResVReg, const SPIRVType *ResType, MachineInstr &I) const {
+  assert(I.getNumOperands() == 3);
+  assert(I.getOperand(2).isReg());
+  MachineBasicBlock &BB = *I.getParent();
+
+  Register BallotReg = MRI->createVirtualRegister(&SPIRV::IDRegClass);
+  SPIRVType *IntTy = GR.getOrCreateSPIRVIntegerType(32, I, TII);
+  SPIRVType *BallotType = GR.getOrCreateSPIRVVectorType(IntTy, 4, I, TII);
+
+  bool Result =
+      BuildMI(BB, I, I.getDebugLoc(), TII.get(SPIRV::OpGroupNonUniformBallot))
+          .addDef(BallotReg)
+          .addUse(GR.getSPIRVTypeID(BallotType))
+          .addUse(GR.getOrCreateConstInt(SPIRV::Scope::Subgroup, I, IntTy, TII))
+          .addUse(I.getOperand(2).getReg());
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pow2clk wrote:

You're missing a `constrainAllUses` call on the end here. `AddUse` returns a reference to `MachineInstrBuilder`, which I'm not really sure how gets converted to a bool, but I don't want to rely on it. 

https://github.com/llvm/llvm-project/pull/113382