On Tue, Feb 04, 2020 at 11:16:06AM +0100, Uros Bizjak wrote:
> I guess that Comment #9 patch form the PR should be trivially correct,
> but althouhg it looks obvious, I don't want to propose the patch since
> I have no means of testing it.
I don't have means of testing it either.
https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention?view=vs-2019
is quite explicit that [xyz]mm16-31 are call clobbered and only xmm6-15 (low
128-bits only) are call preserved.
We are talking e.g. about
/* { dg-options "-O2 -mabi=ms -mavx512vl" } */
typedef double V __attribute__((vector_size (16)));
void foo (void);
V bar (void);
void baz (V);
void
qux (void)
{
V c;
{
register V a __asm ("xmm18");
V b = bar ();
asm ("" : "=x" (a) : "0" (b));
c = a;
}
foo ();
{
register V d __asm ("xmm18");
V e;
d = c;
asm ("" : "=x" (e) : "0" (d));
baz (e);
}
}
where according to the MSDN doc gcc incorrectly holds the c value
in xmm18 register across the foo call; if foo is compiled by some Microsoft
compiler (or LLVM), then it could clobber %xmm18.
If all xmm18 occurrences are changed to say xmm15, then it is valid to hold
the 128-bit value across the foo call (though, surprisingly, LLVM saves it
into stack anyway).
The other parts are I guess mainly about SEH. Consider e.g.
void
foo (void)
{
register double x __asm ("xmm14");
register double y __asm ("xmm18");
asm ("" : "=x" (x));
asm ("" : "=v" (y));
x += y;
y += x;
asm ("" : : "x" (x));
asm ("" : : "v" (y));
}
looking at cross-compiler output, with -O2 -mavx512f this emits
.file "abcdeq.c"
.text
.align 16
.globl foo
.def foo; .scl 2; .type 32; .endef
.seh_proc foo
foo:
subq $40, %rsp
.seh_stackalloc 40
vmovaps %xmm14, (%rsp)
.seh_savexmm %xmm14, 0
vmovaps %xmm18, 16(%rsp)
.seh_savexmm %xmm18, 16
.seh_endprologue
vaddsd %xmm18, %xmm14, %xmm14
vaddsd %xmm18, %xmm14, %xmm18
vmovaps (%rsp), %xmm14
vmovaps 16(%rsp), %xmm18
addq $40, %rsp
ret
.seh_endproc
.ident "GCC: (GNU) 10.0.1 20200207 (experimental)"
Does whatever assembler mingw64 uses even assemble this (I mean the
.seh_savexmm %xmm16, 16 could be problematic)?
I can find e.g.
https://stackoverflow.com/questions/43152633/invalid-register-for-seh-savexmm-in-cygwin/43210527
which then links to
https://gcc.gnu.org/PR65782
2020-02-08 Uroš Bizjak <ubizjak@gmail.com>
Jakub Jelinek <jakub@redhat.com>
PR target/65782
* config/i386/i386.h (CALL_USED_REGISTERS): Make
xmm16-xmm31 call-used even in 64-bit ms-abi.
* gcc.target/i386/pr65782.c: New test.
Co-authored-by: Uroš Bizjak <ubizjak@gmail.com>
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