[llvm] AMDGPU: Select VGPR MFMAs by default (PR #159493)

[Matt Arsenault via llvm-commits]

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@@ -37,7 +37,7 @@ static cl::opt<bool, true> MFMAVGPRFormOpt(
     "amdgpu-mfma-vgpr-form",
     cl::desc("Whether to force use VGPR for Opc and Dest of MFMA. If "
              "unspecified, default to compiler heuristics"),
-    cl::location(SIMachineFunctionInfo::MFMAVGPRForm), cl::init(false),
+    cl::location(SIMachineFunctionInfo::MFMAVGPRForm), cl::init(true),
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arsenm wrote:

But the system always was try to use the VGPR form. Any time we were emitting AGPR MFMAs was essentially an edge case or bug 

https://github.com/llvm/llvm-project/pull/159493