[PATCH] D99352: [AMDGPU] ds_read_*/ds_write_* operations require strict alignment.

[Stanislav Mekhanoshin via Phabricator via llvm-commits]

rampitec added inline comments.


================
Comment at: llvm/lib/Target/AMDGPU/SIISelLowering.cpp:1435
+      // ds_read/write_b128 require 16-byte alignment on gfx8 and older.
+      bool Aligned = Alignment >= Align(16);
       if (IsFast)
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arsenm wrote:
> hsmhsm wrote:
> > arsenm wrote:
> > > I don't like changing this function to lie and say it doesn't work when it does
> > My understanding is that the function allowsMisalignedMemoryAccessesImpl() should check for the strict alignment requirment for ds_read/ds_write operations. I am now further updated this function accordingly.
> You are making this stricter than the instructions really allow
That is more or less the point. I think there is some balance here between the perf drop when a wide access is used for misaligned data and perf loss when a narrow access is used on data for which we cannot prove alignment but it just happens to be aligned.

This seems to warrant a perf testing on this patch. @cfang does this solve perf regression you were working on?


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  https://reviews.llvm.org/D99352/new/

https://reviews.llvm.org/D99352