The documentation of the constraint A says:
"The a and d registers, as a pair (for instructions that return half the result
in one and half in the other)."
So I expect:
asm("/* dx = 0, ax = 1 */" :: "A" ((int32_t)1) );
asm("/* edx = 0, eax = 1 */" :: "A" ((int64_t)1) );
//asm("/* rdx = 0, rax = 1 */" :: "A" ((int128_t)1));
but the behavior of gcc is different:
with -m32 switch:
asm("/* eDX = undef, eax = 1 */" :: "A" ((int32_t)1) );
asm("/* edx = 0, eax = 1 */" :: "A" ((int64_t)1) );
with -m64 switch:
asm("/* rDX = undef, eax = 1 */" :: "A" ((int32_t)1) );
asm("/* rDX = undef, rax = 1 */" :: "A" ((int64_t)1) );
so for -m64 there is no difference between a and A
--
Summary: Inline Assembler: Constraint A expected different
behavior
Product: gcc
Version: 4.4.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: inline-asm
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: andreas dot freimuth at united-bits dot de
GCC build triplet: x86_64-linux-gnu
GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41133
