[llvm] [AMDGPU] Fix Xcnt handling between blocks (PR #165201)

[Jay Foad via llvm-commits]

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@@ -1288,18 +1288,38 @@ void WaitcntBrackets::applyWaitcnt(InstCounterType T, unsigned Count) {
 }
 
 void WaitcntBrackets::applyXcnt(const AMDGPU::Waitcnt &Wait) {
+  // On entry to a block with multiple predescessors, there may
+  // be pending SMEM and VMEM events active at the same time.
+  // In such cases, only clear one active event at a time.
+  auto applyPendingXcntGroup = [this](unsigned E) {
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jayfoad wrote:

Nit: this really should not have "group" in the name. Xcnt insertion has nothing to do with groups. This goes back to #145566 which added the bad names "SMEM_GROUP" and "VMEM_GROUP".

https://github.com/llvm/llvm-project/pull/165201