[PATCH] D138186: InstCombine: Simplify vector load based on demanded elements

[Ruiling, Song via Phabricator via llvm-commits]

ruiling added a comment.

In D138186#3933180 <https://reviews.llvm.org/D138186#3933180>, @piotr wrote:

> I've always thought we didn't have such a transformation in the generic instcombine, because it may hurt some targets, but I don't immediately see how. (We do have a similar one for intrinsic loads in the AMDGPU-specific file).

For X86, the vector load will be scalarized, thus it is easy to be optimized during instruction selection or later on MachineIR. I guess this may contribute to why we were not doing such optimization before. I could not see why this would hurt other targets.



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Comment at: llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp:1716
+      InsertNewInstWith(NewPtr, *LI);
+    InsertNewInstWith(NewLI, *LI);
+    InsertNewInstWith(NewI, *LI);
----------------
piotr wrote:
> Should the original load be replaced rather than kept around?
The original load becomes dead and will be deleted afterwards in this pass.


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