[llvm] Improve selection of conditional branch on amdgcn.ballot!=0 condition in SelectionDAG. (PR #68714)

[Matt Arsenault via llvm-commits]

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@@ -2259,6 +2259,30 @@ bool AMDGPUDAGToDAGISel::isCBranchSCC(const SDNode *N) const {
   return false;
 }
 
+bool isBoolSGPR(SDValue V);
+
+static SDValue combineBallotPattern(SDValue VCMP) {
+  assert(VCMP->getOpcode() == AMDGPUISD::SETCC);
+  // Special case for amdgcn.ballot:
+  // %Cond = i1 (and/or combination of i1 ISD::SETCCs)
+  // %VCMP = i(WaveSize) AMDGPUISD::SETCC (ext %Cond), 0, setne ; lowered ballot
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arsenm wrote:

You might need to handle the negated form as well 

https://github.com/llvm/llvm-project/pull/68714