[PATCH] D119696: [AMDGPU] Improve v_cmpx usage on GFX10.3.

[Sebastian Neubauer via Phabricator via llvm-commits]

sebastian-ne added a reviewer: sebastian-ne.
sebastian-ne added inline comments.


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Comment at: llvm/lib/Target/AMDGPU/SIOptimizeExecMasking.cpp:326-330
+        if (VData && VData->getReg() == Reg)
+          return nullptr;
+
+        if (Addr && Addr->isReg() && Addr->getReg() == Reg)
+          return nullptr;
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I’m not sure what I thought before, but a buffer_store obviously only changes memory and not its register arguments, so it’s completely fine if a buffer_store is between the v_cmp and the s_and_saveexec. Checking modifiesRegister should be enough.


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Comment at: llvm/lib/Target/AMDGPU/SIOptimizeExecMasking.cpp:356
+      TII->getNamedOperand(SaveExec, AMDGPU::OpName::src0);
+  if (!SaveExecSrc0->isReg() || SaveExecSrc0->getSubReg())
+    return nullptr;
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There’s quite a lot of these isReg and !getSubReg checks in this patch. What are they guarding? I replaced them by asserts and there was no amdgpu codegen test that failed. (Leaving aside the isReg test for v_cmp arguments, which can also be constants.)


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Comment at: llvm/lib/Target/AMDGPU/SIOptimizeExecMasking.cpp:645
+        SaveExecInstr->eraseFromParent();
+        VCmpInstr->eraseFromParent();
+      }
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Not sure if this was already mentioned, but do you make sure that the v_cmp is not used anywhere outside the s_saveexec?

I guess it would still be beneficial to insert a v_cmpx if the v_cmp has more uses, but it shouldn’t be removed in that case.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D119696/new/

https://reviews.llvm.org/D119696