[llvm] [AMDGPU] Ignore inactive VGPRs in .vgpr_count (PR #144855)

[Jay Foad via llvm-commits]

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@@ -139,268 +139,56 @@ AMDGPUResourceUsageAnalysis::analyzeResourceUsage(
 
   Info.UsesVCC =
       MRI.isPhysRegUsed(AMDGPU::VCC_LO) || MRI.isPhysRegUsed(AMDGPU::VCC_HI);
+  Info.NumExplicitSGPR = TRI.getNumUsedPhysRegs(MRI, AMDGPU::SGPR_32RegClass,
+                                                /*IncludeCalls=*/false);
+  if (ST.hasMAIInsts())
+    Info.NumAGPR = TRI.getNumUsedPhysRegs(MRI, AMDGPU::AGPR_32RegClass,
+                                          /*IncludeCalls=*/false);
 
-  // If there are no calls, MachineRegisterInfo can tell us the used register
-  // count easily.
   // A tail call isn't considered a call for MachineFrameInfo's purposes.
-  if (!FrameInfo.hasCalls() && !FrameInfo.hasTailCall()) {
-    Info.NumVGPR = TRI.getNumUsedPhysRegs(MRI, AMDGPU::VGPR_32RegClass);
-    Info.NumExplicitSGPR = TRI.getNumUsedPhysRegs(MRI, AMDGPU::SGPR_32RegClass);
-    if (ST.hasMAIInsts())
-      Info.NumAGPR = TRI.getNumUsedPhysRegs(MRI, AMDGPU::AGPR_32RegClass);
+  bool HasCalls = FrameInfo.hasCalls() || FrameInfo.hasTailCall();
+  // Functions that use the llvm.amdgcn.init.whole.wave intrinsic often have
+  // VGPR arguments that are only added for the purpose of preserving the
+  // inactive lanes. These should not be included in the number of used VGPRs.
+  bool NeedsExplicitVGPRCount = MFI->hasInitWholeWave();
+  if (!HasCalls && !NeedsExplicitVGPRCount) {
+
+    Info.NumVGPR = TRI.getNumUsedPhysRegs(MRI, AMDGPU::VGPR_32RegClass,
+                                          /*IncludeCalls=*/false);
     return Info;
   }
 
   int32_t MaxVGPR = -1;
-  int32_t MaxAGPR = -1;
-  int32_t MaxSGPR = -1;
   Info.CalleeSegmentSize = 0;
 
   for (const MachineBasicBlock &MBB : MF) {
     for (const MachineInstr &MI : MBB) {
-      // TODO: Check regmasks? Do they occur anywhere except calls?
-      for (const MachineOperand &MO : MI.operands()) {
-        unsigned Width = 0;
-        bool IsSGPR = false;
-        bool IsAGPR = false;
-
-        if (!MO.isReg())
-          continue;
-
-        Register Reg = MO.getReg();
-        switch (Reg) {
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jayfoad wrote:

Removing this huge switch is great but does it have to be part of this patch? Can it be a separate NFC thing?

https://github.com/llvm/llvm-project/pull/144855