[llvm-branch-commits] [llvm] [AMDGPU] Dynamic VGPR support for llvm.amdgcn.cs.chain (PR #130094)

[Matt Arsenault via llvm-branch-commits]

================
@@ -1200,34 +1225,78 @@ bool AMDGPUCallLowering::lowerTailCall(
   if (!IsSibCall)
     CallSeqStart = MIRBuilder.buildInstr(AMDGPU::ADJCALLSTACKUP);
 
-  unsigned Opc =
-      getCallOpcode(MF, Info.Callee.isReg(), true, ST.isWave32(), CalleeCC);
+  bool IsChainCall = AMDGPU::isChainCC(Info.CallConv);
+  bool IsDynamicVGPRChainCall = false;
+
+  if (IsChainCall) {
+    ArgInfo FlagsArg = Info.OrigArgs[ChainCallArgIdx::Flags];
+    const APInt &FlagsValue = cast<ConstantInt>(FlagsArg.OrigValue)->getValue();
+    if (FlagsValue.isZero()) {
+      if (Info.OrigArgs.size() != 5) {
+        LLVM_DEBUG(dbgs() << "No additional args allowed if flags == 0");
+        return false;
+      }
+    } else if (FlagsValue.isOneBitSet(0)) {
+      IsDynamicVGPRChainCall = true;
+
+      if (Info.OrigArgs.size() != 8) {
+        LLVM_DEBUG(dbgs() << "Expected 3 additional args");
+        return false;
+      }
+
+      // On GFX12, we can only change the VGPR allocation for wave32.
+      if (!ST.isWave32()) {
+        LLVM_DEBUG(dbgs() << "Dynamic VGPR mode is only supported for wave32");
----------------
arsenm wrote:

```suggestion
        LLVM_DEBUG(dbgs() << "Dynamic VGPR mode is only supported for wave32\n");
```

https://github.com/llvm/llvm-project/pull/130094