This is not meant to be a long-term solution, but it's the easiest thing
to get working quickly at the moment. The main intention of this hack is
to allow more tests to be enabled. By the time the coff linker is far
enough along to be enabled by default, this will no longer be required.
If you write an if expression in mem.doNotOptimizeAway like
doNotOptimizeAway(if (ix < 0x00100000) x / 0x1p120 else x + 0x1p120);,
FCSEL instruction is used on AArch64.
FCSEL instruction selects one of the two registers according to
the condition and copies its value.
In this example, `x / 0x1p120` and `x + 0x1p120` are expressions
that raise different floating-point exceptions.
However, since both are actually evaluated before the FCSEL
instruction, the exception not intended by the programmer may
also be raised.
To prevent FCSEL instruction from being used here, this commit
splits doNotOptimizeAway in two.
This prevents symbols from these libraries from polluting the dynamic symbol
tables of binaries built with Zig. The downside is that we no longer deduplicate
the symbols at run time due to weak linkage.
Closes#7935.
Closes#13303.
Closes#19342.
Functions like isMinGW() and isGnuLibC() have a good reason to exist: They look
at multiple components of the target. But functions like isWasm(), isDarwin(),
isGnu(), etc only exist to save 4-8 characters. I don't think this is a good
enough reason to keep them, especially given that:
* It's not immediately obvious to a reader whether target.isDarwin() means the
same thing as target.os.tag.isDarwin() precisely because isMinGW() and similar
functions *do* look at multiple components.
* It's not clear where we would draw the line. The logical conclusion before
this commit would be to also wrap Arch.isX86(), Os.Tag.isSolarish(),
Abi.isOpenHarmony(), etc... this obviously quickly gets out of hand.
* It's nice to just have a single correct way of doing something.
When using the LLVM backend, array copies were lowered as calls to
`llvm.memcpy.*` builtin which could cause recursive calls to memcpy to
be generated (observed with `-target x86_64-linux -mcpu x86_64+avx512vl
--debug-rt`).
By instead performing these small fixed-size copies with integers or
vectors the LLVM backend does not generate calls to the `llvm.memcpy`
builtin, and so (with `-fno-builtin`) recursive calls to memcpy will
not be generated by LLVM.
The assertions and (test build) runtime safety have been removed as they
may cause (mutually) recursive calls to memcpy in debug builds since the
panic handler generates calls to llvm.memcpy.
The new memcpy function aims to be more generic than the previous
implementation which was adapted from an implementation optimized for
x86_64 avx2 machines. Even on x86_64 avx2 machines this implementation
should be generally be faster due to fewer branches in the small length
cases and generating less machine code.
Note that the new memcpy function no longer acts as a memmove.
