[PATCH] D66606: IR. Change strip* family of functions to not look through aliases.

[Peter Collingbourne via Phabricator via cfe-commits]

pcc created this revision.
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I noticed another instance of the issue where references to aliases were
being replaced with aliasees, this time in InstCombine. In the instance that
I saw it turned out to be only a QoI issue (a symbol ended up being missing
from the symbol table due to the last reference to the alias being removed,
preventing HWASAN from symbolizing a global reference), but it could easily
have manifested as incorrect behaviour.

Since this is the third such issue encountered (previously: D65118 <https://reviews.llvm.org/D65118>, D65314 <https://reviews.llvm.org/D65314>)
it seems to be time to address this common error/QoI issue once and for all
and make the strip* family of functions not look through aliases.

Includes a test for the specific issue that I saw, but no doubt there are
other similar bugs fixed here.

As with D65118 <https://reviews.llvm.org/D65118> this has been tested to make sure that the optimization isn't
load bearing. I built Clang, Chromium for Linux, Android and Windows as well
as the test-suite and there were no size regressions.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D66606

Files:
  clang/lib/CodeGen/CGExpr.cpp
  llvm/include/llvm/IR/Value.h
  llvm/lib/Analysis/ConstantFolding.cpp
  llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
  llvm/lib/Analysis/StackSafetyAnalysis.cpp
  llvm/lib/CodeGen/Analysis.cpp
  llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
  llvm/lib/IR/Constants.cpp
  llvm/lib/IR/Module.cpp
  llvm/lib/IR/Value.cpp
  llvm/lib/IR/Verifier.cpp
  llvm/lib/Target/WebAssembly/WebAssemblyLowerGlobalDtors.cpp
  llvm/lib/Transforms/IPO/ConstantMerge.cpp
  llvm/lib/Transforms/IPO/GlobalOpt.cpp
  llvm/test/Transforms/InstCombine/bitcast-alias-function.ll
  llvm/test/Transforms/InstCombine/bitcast-function.ll
  llvm/test/Transforms/InstCombine/gep-alias.ll
  llvm/test/Transforms/InstCombine/pr39177.ll

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