[llvm-bugs] [Bug 42830] New: Incorrect register allocation for inline assembly with 4 outputs

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42830

            Bug ID: 42830
           Summary: Incorrect register allocation for inline assembly with
                    4 outputs
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: glider at google.com
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, spatel+llvm at rotateright.com

When compiling the following code:

$ cat bar.c
char foo();

int bar() {
    char x1 = foo();
    char x2 = foo();
    char x3 = foo();
    char y1, y2, y3, y4;
    asm("mov $1, %k0\nmov $2, %k1\nmov $3, %k2\nmov $4, %k3" : "=r"(y1),
"=r"(y2), "=r"(y3), "=r"(y4));
    return x1 + x2 + y1 + y2 + y3 + y4;
}

with -m32, Clang uses EAX twice to return 1 and 4 from the inline assembly:

$ clang bar.c -c -m32
$ objdump -dr bar.o

00000000 <bar>:
   0:   55                      push   %ebp
   1:   89 e5                   mov    %esp,%ebp
   3:   57                      push   %edi
   4:   56                      push   %esi
   5:   83 ec 10                sub    $0x10,%esp
   8:   e8 fc ff ff ff          call   9 <bar+0x9>
                        9: R_386_PC32   foo
   d:   88 45 f7                mov    %al,-0x9(%ebp)
  10:   e8 fc ff ff ff          call   11 <bar+0x11>
                        11: R_386_PC32  foo
  15:   88 45 f6                mov    %al,-0xa(%ebp)
  18:   e8 fc ff ff ff          call   19 <bar+0x19>
                        19: R_386_PC32  foo
  1d:   88 45 f5                mov    %al,-0xb(%ebp)
  20:   b8 01 00 00 00          mov    $0x1,%eax
  25:   b9 02 00 00 00          mov    $0x2,%ecx
  2a:   ba 03 00 00 00          mov    $0x3,%edx
  2f:   b8 04 00 00 00          mov    $0x4,%eax


Without -m32 Clang returns 1 and 4 in EAX and ESI, respectively.

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