[llvm] [AMDGPU] Merge consecutive wait_alu instruction (PR #128916)

[Nicolai Hähnle via llvm-commits]

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@@ -164,6 +164,48 @@ class AMDGPUWaitSGPRHazards {
       BuildMI(MBB, MI, MI->getDebugLoc(), TII->get(AMDGPU::DS_NOP));
   }
 
+  unsigned mergeMasks(unsigned Mask1, unsigned Mask2) {
+    unsigned Mask = 0xffff;
+    Mask = AMDGPU::DepCtr::encodeFieldSaSdst(
+        Mask, std::min(AMDGPU::DepCtr::decodeFieldSaSdst(Mask1),
+                       AMDGPU::DepCtr::decodeFieldSaSdst(Mask2)));
+    Mask = AMDGPU::DepCtr::encodeFieldVaVcc(
+        Mask, std::min(AMDGPU::DepCtr::decodeFieldVaVcc(Mask1),
+                       AMDGPU::DepCtr::decodeFieldVaVcc(Mask2)));
+    Mask = AMDGPU::DepCtr::encodeFieldVmVsrc(
+        Mask, std::min(AMDGPU::DepCtr::decodeFieldVmVsrc(Mask1),
+                       AMDGPU::DepCtr::decodeFieldVmVsrc(Mask2)));
+    Mask = AMDGPU::DepCtr::encodeFieldVaSdst(
+        Mask, std::min(AMDGPU::DepCtr::decodeFieldVaSdst(Mask1),
+                       AMDGPU::DepCtr::decodeFieldVaSdst(Mask2)));
+    Mask = AMDGPU::DepCtr::encodeFieldVaVdst(
+        Mask, std::min(AMDGPU::DepCtr::decodeFieldVaVdst(Mask1),
+                       AMDGPU::DepCtr::decodeFieldVaVdst(Mask2)));
+    Mask = AMDGPU::DepCtr::encodeFieldHoldCnt(
+        Mask, std::min(AMDGPU::DepCtr::decodeFieldHoldCnt(Mask1),
+                       AMDGPU::DepCtr::decodeFieldHoldCnt(Mask2)));
+    Mask = AMDGPU::DepCtr::encodeFieldVaSsrc(
+        Mask, std::min(AMDGPU::DepCtr::decodeFieldVaSsrc(Mask1),
+                       AMDGPU::DepCtr::decodeFieldVaSsrc(Mask2)));
+    return Mask;
+  }
+
+  bool mergeConsecutiveWaitAlus(MachineBasicBlock::instr_iterator &MI,
+                                unsigned Mask) {
+    auto MBB = MI->getParent();
+    if (MI == MBB->instr_begin())
+      return false;
+
+    auto It = prev_nodbg(MI, MBB->instr_begin());
+    if (It->getOpcode() != AMDGPU::S_WAITCNT_DEPCTR)
+      return false;
+
+    It->getOperand(0).setImm(mergeMasks(Mask, It->getOperand(0).getImm()));
+    return true;
+
+    return false;
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nhaehnle wrote:

Spurious return false.

https://github.com/llvm/llvm-project/pull/128916