[InstCombine] Optimistically allow multiple shufflevector uses in foldOpPhi (#114278)
We would like to optimize situations of the form that happen after loop
vectorization+SROA:
```
loop:
%phi = phi zeroinitializer, %interleaved
%deinterleave_a = shufflevector %phi, poison ; pick half of the lanes
%deinterleave_b = shufflevector %phi, posion ; pick remaining lanes
... %a = ... %b = ...
%interleaved = shufflevector %a, %b ; interleave lanes of a+b
```
where the interleave and de-interleave shuffle operations cancel each
other out.
This could be handled by `foldOpPhi` but does not currently work because
it does
not proceed when there are multiple uses of the `Phi` operation.
This extends `foldOpPhi` to allow multiple `shufflevector` uses when
they are
shown to simplify for all `Phi` input values.
Welcome to the LLVM project!
This repository contains the source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and run-time environments.
The LLVM project has multiple components. The core of the project is itself called “LLVM”. This contains all of the tools, libraries, and header files needed to process intermediate representations and convert them into object files. Tools include an assembler, disassembler, bitcode analyzer, and bitcode optimizer.
C-like languages use the Clang frontend. This component compiles C, C++, Objective-C, and Objective-C++ code into LLVM bitcode -- and from there into object files, using LLVM.
Other components include: the libc++ C++ standard library, the LLD linker, and more.
Consult the Getting Started with LLVM page for information on building and running LLVM.
For information on how to contribute to the LLVM project, please take a look at the Contributing to LLVM guide.
Join the LLVM Discourse forums, Discord chat, LLVM Office Hours or Regular sync-ups.
The LLVM project has adopted a code of conduct for participants to all modes of communication within the project.