[llvm] [AMDGPU][SIInsertWaitcnts] Do not add s_waitcnt when the counters are known to be 0 already (PR #72830)

[Jay Foad via llvm-commits]

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@@ -886,34 +900,39 @@ bool SIInsertWaitcnts::applyPreexistingWaitcnt(
     if (II.isMetaInstruction())
       continue;
 
-    if (II.getOpcode() == AMDGPU::S_WAITCNT) {
-      // Conservatively update required wait if this waitcnt was added in an
-      // earlier pass. In this case it will not exist in the tracked waitcnt
-      // set.
-      if (!TrackedWaitcntSet.count(&II)) {
-        unsigned IEnc = II.getOperand(0).getImm();
-        AMDGPU::Waitcnt OldWait = AMDGPU::decodeWaitcnt(IV, IEnc);
-        Wait = Wait.combined(OldWait);
-      }
+    unsigned Opcode = II.getOpcode();
+    bool CanFullyDiscardWaitcntSequence = SIInstrInfo::isSoftWaitcnt(Opcode);
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jayfoad wrote:

Maybe just call this `IsSoft`?

https://github.com/llvm/llvm-project/pull/72830