tree c74d4036841aeae35a602c3f0f39201e2091ab0d
parent 50066a3edffa96879ad1545a8e61c009c86c6e71
author Reid Kleckner <rnk@google.com> 1599762222 -0700
committer Antonio Maiorano <amaiorano@google.com> 1605714769 +0000

Use pragmas to work around MSVC x86_32 debug miscompile bug

Halide users reported this here: https://llvm.org/pr46176
I reported the issue to MSVC here:
https://developercommunity.visualstudio.com/content/problem/1179643/msvc-copies-overaligned-non-trivially-copyable-par.html

This codepath is apparently not covered by LLVM's unit tests, so I added
coverage in a unit test.

If we want to support this configuration going forward, it means that is
in general not safe to pass a SmallVector<T, N> by value if alignof(T)
is greater than 4. This doesn't appear to come up often because passing
a SmallVector by value is inefficient and not idiomatic: it copies the
inline storage. In this case, the SmallVector<LLT,4> is captured by
value by a lambda, and the lambda is passed by value into std::function,
and that's how we hit the bug.

Differential Revision: https://reviews.llvm.org/D87475

NOTE from amaiorano@ : applied this LLVM patch (without the unittest) to SwiftShader.

Bug: b/173512119
Change-Id: If036f61386b51f9b4a20427812b4ac92d901244d
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/50469
Tested-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>