[Bug target/104704] New: [12 Regression] ix86_gen_scratch_sse_rtx doesn't work explicit XMM7/XMM15/XMM31 usage

["hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104704

            Bug ID: 104704
           Summary: [12 Regression] ix86_gen_scratch_sse_rtx doesn't work
                    explicit XMM7/XMM15/XMM31 usage
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com
                CC: crazylht at gmail dot com, ubizjak at gmail dot com
  Target Milestone: ---

ix86_gen_scratch_sse_rtx returns XMM7/XMM15/XMM31 as a scratch register to
prevent RTL optimizer from removing scratch vector register.  But it introduces
a conflict with explicit XMM7/XMM15/XMM31 usage:

[hjl@gnu-tgl-2 scratch-2]$ cat x-2.c 
/* { dg-do compile { target { ! ia32 } } } */
/* { dg-options "-O2 -march=x86-64 -mavx2" } */

#include <immintrin.h>

__m256d y, z;

int i;

__attribute__((noipa))
int
do_test (void)
{
  register int xmm15 __asm ("xmm15") = i;
  asm volatile ("" : "+v" (xmm15));
  z = y;
  register int xmm2 __asm ("xmm2") = xmm15;
  asm volatile ("" : "+v" (xmm2));
  return xmm2;
}

__attribute__((target("arch=x86-64")))
int
main (void)
{
 if (__builtin_cpu_supports ("avx2"))
   {
     i = 4;
     if (do_test () != 4)
       __builtin_abort ();
   }
  return 0;
}
[hjl@gnu-tgl-2 scratch-2]$ make x-2
/export/build/gnu/tools-build/gcc-debug/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/tools-build/gcc-debug/build-x86_64-linux/gcc/ -O2
-march=x86-64 -mavx2 -S x-2.c
/export/build/gnu/tools-build/gcc-debug/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/tools-build/gcc-debug/build-x86_64-linux/gcc/ -O2
-march=x86-64 -o x-2 x-2.s
[hjl@gnu-tgl-2 scratch-2]$ ./x-2
Aborted (core dumped)
[hjl@gnu-tgl-2 scratch-2]$