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[release/3.1] Fix build with Clang 13 (#63314) #28232
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* Fix clang 13 induced runtime issues (#62170) The clang 13 optimizer started to assume that "this" pointer is always properly aligned. That lead to elimination of some code that was actually needed. It also takes pointer aliasing rules more strictly in one place in jit. That caused the optimizer to falsely assume that a callee with an argument passed by reference is not modifying that argument and used a stale copy of the original value at the caller site. This change fixes both of the issues. With this fix, runtime compiled using clang 13 seems to be fully functional.
janvorli
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jeffschwMSFT
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Jan 31, 2022
leecow
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@safern is it time to merge these prs for the next release? |
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Port fix of build using Clang 13 to release/3.1. Backport of dotnet/runtime#63314
Customer Impact
The recently released Clang 13 has started to apply assumption that this pointer is always aligned to the natural alignment of the object. These break compilation of .NET Core 3.1 e.g. on Fedora 35 where Clang 13 is the one installed. This issue was reported by Red Hat developers.
Testing
Local builds of release and debug versions using clang 9 and clang 13
Risk
Low, there are no functional changes and the fix has been in main and release/6.0 branches for about 2 months.
Original commit message:
The clang 13 optimizer started to assume that "this" pointer is always
properly aligned. That lead to elimination of some code that was actually
needed.
It also takes pointer aliasing rules more strictly in one place in jit.
That caused the optimizer to falsely assume that a callee with an argument
passed by reference is not modifying that argument and used a stale
copy of the original value at the caller site.
This change fixes both of the issues. With this fix, runtime compiled
using clang 13 seems to be fully functional.
cc @janvorli