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

[Juan Manuel Martinez Caamaño via llvm-commits]

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@@ -45,6 +45,7 @@ define void @back_off_barrier_no_fence(ptr %in, ptr %out) #0 {
 ; GFX11-BACKOFF-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GFX11-BACKOFF-NEXT:    flat_load_b32 v0, v[0:1]
 ; GFX11-BACKOFF-NEXT:    s_waitcnt vmcnt(0) lgkmcnt(0)
+; GFX11-BACKOFF-NEXT:    s_waitcnt_vscnt null, 0x0
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jmmartinez wrote:

Hello!

In an initial version of the patch, before we introduced de soft-waitcnts, setting the counters to 0 in the initial state would end up removing the "s_waitcnt 0" placed at non-kernel function entry. This is not needed anymore since we make the distinction between soft/strong waitcnts. However, we still have to do it for vscnt as jay said.

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