[llvm] [AMDGPU] Provide control to force VGPR MFMA form (PR #148079)

[Matt Arsenault via llvm-commits]

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@@ -69,8 +79,8 @@ SIMachineFunctionInfo::SIMachineFunctionInfo(const Function &F,
     PSInputAddr = AMDGPU::getInitialPSInputAddr(F);
   }
 
-  MayNeedAGPRs = ST.hasMAIInsts();
-  if (ST.hasGFX90AInsts() &&
+  MayNeedAGPRs = ST.hasMAIInsts() && !MFMAVGPRForm;
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arsenm wrote:

This breaks if used with gfx908, so it's impossible to flip the default 

https://github.com/llvm/llvm-project/pull/148079