change semantics of @memcpy and @memset
#15278
Merged
Commits on Apr 25, 2023
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change semantics of
@memcpyand@memsetNow they use slices or array pointers with any element type instead of requiring byte pointers. This is a breaking enhancement to the language. The safety check for overlapping pointers will be implemented in a future commit. closes #14040
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update
@memcpyto require equal src and dest lens* Sema: upgrade operands to array pointers if possible when emitting AIR. * Implement safety checks for length mismatch and aliasing. * AIR: make ptrtoint support slice operands. Implement in LLVM backend. * C backend: implement new `@memset` semantics. `@memcpy` is not done yet.
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LLVM backend: support non-byte-sized memset
Also introduce memset_safe AIR tag and support it in C backend and LLVM backend.
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C backend: fix memset for loop lowering
Previously, this code casted the array pointer to u8 pointer, but I removed that in a different commit. This commit restores the cast, but instead of hard-coding u8, it uses the destination element pointer, since memset now supports arbitrary element types.
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add behavior test for
@memseton slicesand avoid new language feature in std.ArrayList for now, until x86_64 self-hosted backend can implement it.
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x86_64 backend: implement
@memsetfor element ABI size > 1* make memset and memset_safe guarantee that if the length is comptime-known then it will be nonzero.
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Needed due to the compiler depending on standard library APIs such as ArrayList that contain `@memset` and `@memcpy` calls in them. The number of parameters changed, so this is necessary for the compiler to build.
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C backend: use ++ instead of += for airMemset
It does the same thing but has fewer bytes in the output.
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stage2: introduce store_safe AIR instruction
store: The value to store may be undefined, in which case the destination memory region has undefined bytes after this instruction is evaluated. In such case ignoring this instruction is legal lowering. store_safe: Same as `store`, except if the value to store is undefined, the memory region should be filled with 0xaa bytes, and any other safety metadata such as Valgrind integrations should be notified of this memory region being undefined.
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Sema: fix memcpy alias safety incorrect math
Previously it was not multiplying by the element ABI size. Now, it uses ptr_add instructions which do math based on the element type.
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C backend: fix lowering comparison when array ptr meets ptr
Pointer comparisons were triggering `-Wcompare-distinct-pointer-types` before this fix, which adds `(void*)` casts if the lhs type and rhs type do not match pointer sizeness.
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