[llvm] [AMDGPU] Add function attribute to disable TBUFFER combine (PR #156454)

[Piotr Sobczak via llvm-commits]

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@@ -195,6 +195,9 @@ SIMachineFunctionInfo::SIMachineFunctionInfo(const Function &F,
     VGPRForAGPRCopy =
         AMDGPU::VGPR_32RegClass.getRegister(ST.getMaxNumVGPRs(F) - 1);
   }
+
+  if (F.hasFnAttribute("amdgpu-disable-tbuffer-combine"))
+    setDisableTBufferCombine(true);
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piotrAMD wrote:

I think Matt's suggestion was that the conservative behaviour should be the default, so the tbuffer merging should be disabled by default, and only enabled when an attribute is set.

https://github.com/llvm/llvm-project/pull/156454