[Bug c/82028] New: Windows x86_64 should not pass float aggregates in xmm

[jistone at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82028

            Bug ID: 82028
           Summary: Windows x86_64 should not pass float aggregates in xmm
           Product: gcc
           Version: 7.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jistone at redhat dot com
  Target Milestone: ---

Given this input foo.c:

#include <math.h>
typedef struct { double x; } Foo;
Foo foo(Foo f) {
        f.x = fabs(f.x);
        return f;
}

mingw-gcc produces code that uses XMM0 for both the argument and return.

0000000000000000 <foo>:
   0:   55                      push   %rbp
   1:   48 89 e5                mov    %rsp,%rbp
   4:   f2 0f 11 45 10          movsd  %xmm0,0x10(%rbp)
   9:   f2 0f 10 4d 10          movsd  0x10(%rbp),%xmm1
   e:   f3 0f 7e 05 00 00 00    movq   0x0(%rip),%xmm0        # 16 <foo+0x16>
  15:   00
  16:   66 0f 54 c1             andpd  %xmm1,%xmm0
  1a:   f2 0f 11 45 10          movsd  %xmm0,0x10(%rbp)
  1f:   f2 0f 10 45 10          movsd  0x10(%rbp),%xmm0
  24:   5d                      pop    %rbp
  25:   c3                      retq

MSVC passes the argument in RCX and the return value in RAX:

0000000000000000 <foo>:
   0:   48 89 4c 24 08          mov    %rcx,0x8(%rsp)
   5:   48 83 ec 28             sub    $0x28,%rsp
   9:   f2 0f 10 44 24 30       movsd  0x30(%rsp),%xmm0
   f:   e8 00 00 00 00          callq  14 <foo+0x14>
  14:   f2 0f 11 44 24 30       movsd  %xmm0,0x30(%rsp)
  1a:   48 8b 44 24 30          mov    0x30(%rsp),%rax
  1f:   48 83 c4 28             add    $0x28,%rsp
  23:   c3                      retq

And mingw-clang uses RCX/RAX like MSVC:

0000000000000000 <foo>:
   0:   48 83 ec 10             sub    $0x10,%rsp
   4:   48 89 0c 24             mov    %rcx,(%rsp)
   8:   f2 0f 10 04 24          movsd  (%rsp),%xmm0
   d:   0f 28 0d 00 00 00 00    movaps 0x0(%rip),%xmm1        # 14 <foo+0x14>
  14:   66 0f db c1             pand   %xmm1,%xmm0
  18:   f2 0f 11 04 24          movsd  %xmm0,(%rsp)
  1d:   48 8b 0c 24             mov    (%rsp),%rcx
  21:   48 89 4c 24 08          mov    %rcx,0x8(%rsp)
  26:   48 8b 44 24 08          mov    0x8(%rsp),%rax
  2b:   48 83 c4 10             add    $0x10,%rsp
  2f:   c3                      retq



$ gcc -v
Using built-in specs.
COLLECT_GCC=C:\msys64\mingw64\bin\gcc.exe
COLLECT_LTO_WRAPPER=C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/7.2.0/lto-wrapper.exe
Target: x86_64-w64-mingw32
Configured with: ../gcc-7.2.0/configure --prefix=/mingw64
--with-local-prefix=/mingw64/local --build=x86_64-w64-mingw32
--host=x86_64-w64-mingw32 --target=x86_64-w64-mingw32
--with-native-system-header-dir=/mingw64/x86_64-w64-mingw32/include
--libexecdir=/mingw64/lib --enable-bootstrap --with-arch=x86-64
--with-tune=generic --enable-languages=c,lto,c++,objc,obj-c++,fortran,ada
--enable-shared --enable-static --enable-libatomic --enable-threads=posix
--enable-graphite --enable-fully-dynamic-string --enable-libstdcxx-time=yes
--disable-libstdcxx-pch --disable-libstdcxx-debug --disable-isl-version-check
--enable-lto --enable-libgomp --disable-multilib --enable-checking=release
--disable-rpath --disable-win32-registry --disable-nls --disable-werror
--disable-symvers --with-libiconv --with-system-zlib --with-gmp=/mingw64
--with-mpfr=/mingw64 --with-mpc=/mingw64 --with-isl=/mingw64
--with-pkgversion='Rev1, Built by MSYS2 project'
--with-bugurl=https://sourceforge.net/projects/msys2 --with-gnu-as
--with-gnu-ld
Thread model: posix
gcc version 7.2.0 (Rev1, Built by MSYS2 project)

$ clang -v
clang version 4.0.0 (tags/RELEASE_400/final)
Target: x86_64-w64-windows-gnu
Thread model: posix
InstalledDir: C:\msys64\mingw64\bin

>cl
Microsoft (R) C/C++ Optimizing Compiler Version 19.00.24210 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.