Complex layout phase 2 - #159981
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I think you'll also want tests for functions like safe fn complex_float_align2(_: c_float, value: Complex<c_float>) -> Complex<c_float>
also tests for properly handling complex arguments that could be split between registers and the stack (so the previous args take all but 1 fp or int reg), since different ABIs say to do different things (e.g. keep them together on the stack or split between registers and the stack)
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I've added a bunch more tests for that sort of scenario, and integrated my LLVM PRs (for mips, powerpc and sparc) so they now all match.
We should also run abi-cafe (and add complex support) to be fully sure, but for that we'd need to merge this first really.
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| // register alignment of 8 bytes. | ||
| // | ||
| // NOTE: clang uses a vector (e.g. <2 x f32>) here, but if we try that we run into | ||
| // ABI issues because vectors require the altivec target feature. |
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idk how you're getting that, from my testing clang 22 passes complex f32 via an indirect pointer and doesn't use any vector types:
https://clang.godbolt.org/z/676ajoT6a
assuming clang is correct, we should try to generate the same LLVM IR function signature, since that makes cross-language LTO work much better.
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assuming clang is correct
It is not.
- PowerPC ABI incompatibility with GNU on complex arguments llvm/llvm-project#56023
- [clang][PowerPC] Add flag to enable compatibility with GNU for complex arguments llvm/llvm-project#77732
- [PowerPC] make
_ComplexABI GCC-compatible llvm/llvm-project#208917
Being compatible with the standard C compiler on the platform (that determines the ABI of libcalls etc) seems more important than LTO for _Complex. Anyhow, I'm trying to fix the discrepancy in that bottom PR.
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This matters e.g. for
// main.c
#include <stdio.h>
#include <complex.h>
int main(void) {
volatile float re = -1.0f, im = 0.0f;
_Complex float s = csqrtf(re + im * I);
printf("%f + %fi\n", crealf(s), cimagf(s));
return 0;
}with
powerpc-linux-gnu-gcc -O2 main.c -o gcc.out -lm
# Use clang to compile, GCC as the linker.
clang --target=powerpc-linux-gnu -O2 -c main.c -o clang.o
powerpc-linux-gnu-gcc clang.o -o clang.out -lm
echo "gcc"
qemu-ppc -L /usr/powerpc-linux-gnu ./gcc.out
echo "clang"
qemu-ppc -L /usr/powerpc-linux-gnu ./clang.outreturns
gcc
0.000000 + 1.000000i
clang
4.186081 + 0.000000i
The clang result is nonsense.
rust does not emit `byval` here (also not for normal structs) while clang does.
so that we can specify more than one i32 of padding.
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tracking issue: #154023
Follow-up to #158885