JIT: Assume allocations succeed #82961
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We call a NOMEM function when allocations fail that is already marked as no-return, but at least MSVC is not able to pick up on this fact. The result is that all operator new calls end up with an unnecessary null check. This adds an __assume to allow MSVC to recognize that allocations never fail. For other compilers, it uses the preexisting UNREACHABLE() macro, but MSVC was not able to recognize this either. There was also a workaround for an old VSW bug that I've removed.
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch, @kunalspathak Issue DetailsWe call a NOMEM function when allocations fail that is already marked as no-return, but at least MSVC is not able to pick up on this fact. The result is that all operator new calls end up with an unnecessary null check. This adds an __assume to allow MSVC to recognize that allocations never fail. For other compilers, it uses the preexisting UNREACHABLE() macro, but MSVC was not able to recognize this either. There was also a workaround for an old VSW bug that I've removed.
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cc @dotnet/jit-contrib |
src/coreclr/jit/alloc.h
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| #if defined(_MSC_VER) | ||
| // MSVC does not handle the other pattern correctly to recognize this fact. | ||
| __assume(p != nullptr); | ||
| #elif !defined(DEBUG) | ||
| if (p == nullptr) | ||
| { | ||
| UNREACHABLE(); | ||
| } | ||
| #endif |
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Should there be a general ASSUME(expr) helper that abstracts this?
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It turns out there is already a COMPILER_ASSUME next to UNREACHABLE that ends up being __assume with the specified expression on MSVC, so I've switched to that.
We call a NOMEM function when allocations fail that is already marked as no-return, but at least MSVC is not able to pick up on this fact. The result is that all operator new calls end up with an unnecessary null check. This adds an __assume to allow MSVC to recognize that allocations never fail. For other compilers, it uses the preexisting UNREACHABLE() macro, but MSVC was not able to recognize this either.
There was also a workaround for an old VSW bug that I've removed.