[Bug middle-end/85344] New: Constant constraint check sign extends unsigned constant input operands

[thopre01 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85344

            Bug ID: 85344
           Summary: Constant constraint check sign extends unsigned
                    constant  input operands
           Product: gcc
           Version: 8.0.1
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: thopre01 at gcc dot gnu.org
          Reporter: thopre01 at gcc dot gnu.org
  Target Milestone: ---
            Target: arm-none-eabi

Hi,

Compiling the following piece of code with -mthumb -mcpu=cortex-m0 generates an
"impossible constraint in 'asm' error"

void
foo (void)
{
  __asm( "%0" :: "I" ((unsigned char) 0x80));
}

It appears that although the operand is unsigned, it gets sign extended to
perform the constraint check.