[PATCH] D108757: [X86][Codegen] PR51615: don't replace wide volatile load with narrow broadcast-from-memory

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


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Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:5047
+  return !Ld->isVolatile() ||
+         Ld->getValueSizeInBits(0) == EltVT.getScalarSizeInBits();
+}
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spatel wrote:
> I'm not sure if the semantics on this are settled - what happens if the overall size matches, but the "shape" isn't the same?
> I'm imagining something like:
>   %i = load volatile <2 x float>, <2 x float>* @test5_id12345, align 16
>   %b = bitcast <2 x float> %i to <1 x double>
>   %i1 = shufflevector <1 x double> %b, <1 x double> poison, <4 x i32> <i32 undef, i32 0, i32 undef, i32 0>
I don't see why the "shape" would matter. it's either a single load of the same size or it's not.
https://llvm.org/docs/LangRef.html#volatile-memory-accesses notes
> <...> the backend should never split or merge target-legal volatile load/store instructions. Similarly, IR-level volatile loads and stores cannot change from integer to floating-point or vice versa.


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https://reviews.llvm.org/D108757