[llvm] AMDGPU/GlobalISel: Fix inst-selection of ballot (PR #109986)

[Matt Arsenault via llvm-commits]

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@@ -1429,34 +1429,57 @@ bool AMDGPUInstructionSelector::selectBallot(MachineInstr &I) const {
   std::optional<ValueAndVReg> Arg =
       getIConstantVRegValWithLookThrough(I.getOperand(2).getReg(), *MRI);
 
-  const auto BuildCopy = [&](Register SrcReg) {
-    if (Size == STI.getWavefrontSize()) {
-      BuildMI(*BB, &I, DL, TII.get(AMDGPU::COPY), DstReg)
-          .addReg(SrcReg);
-      return;
-    }
+  const auto BuildAnd = [&](unsigned Opcode, Register Dst, Register Src,
+                            Register Exec) {
+    auto And = BuildMI(*BB, &I, DL, TII.get(Opcode), Dst)
+                   .addReg(Src)
+                   .addReg(Exec)
+                   .setOperandDead(3); // Dead scc
+    constrainSelectedInstRegOperands(*And, TII, TRI, RBI);
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arsenm wrote:

Should check return value 

https://github.com/llvm/llvm-project/pull/109986