https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121198
Bug ID: 121198
Summary: [avr][hreg-constraints] error: 'asm' operand has
impossible constraints or there are not enough
registers
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: gjl at gcc dot gnu.org
Target Milestone: ---
The following test case is a very common scenario where a 16-bit register x is
extended to something wider like y. x occupies two 8-bit registers, y occupies
four:
// x comes in in r24..r25.
long foo (int x)
{
long y;
// y occupies r22..r25.
// x occupies r22..r23.
__asm volatile ("; %0" : "={r22}" (y) : "{r22}" (x));
// Return in r22..r25.
return y;
}
Compile with:
$ avr-gcc foo.c -S -dp -mmcu=atmega8
foo.c: In function 'foo':
foo.c:7:5: error: 'asm' operand has impossible constraints or there are not
enough registers
7 | __asm volatile ("; %0" : "={r22}" (y) : "{r22}" (x));
| ^~~~~
IMO the test case above should work, just like
long bar (int x)
{
register long y __asm("22");
register int r22 __asm("22") = x;
__asm volatile ("; %0, %1" : "=r" (y) : "r" (r22));
return y;
}
Configured with: ../../source/gcc-master/configure --target=avr
--enable-languages=c,c++ --disable-nls --disable-libcc1 -with-gnu-ld
--with-gnu-as --with-long-double=64
