http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56715
Bug #: 56715
Summary: Explicit Reg Vars are being ignored for consts when
using g++
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: goswin-...@web.de
Created attachment 29714
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29714
example source that experiences the bug
I'm trying to pass a value to an `asm' operand using a specific register for
arm with a freestanding compiler. Following the example from the info pages I
have the following code:
void foo() {
register const int r4 asm("r4") = 0x1000;
asm volatile("swi #1" : : "r"(r4));
}
void bar() {
register int r4 asm("r4") = 0x1000;
asm volatile("swi #1" : : "r"(r4));
}
Both foo() and bar() compile correct when using gcc. But when using g++ the
foo() function suddenly uses the "r3" register instead of "r4". The bar()
function remains correct.
% arm-none-eabi-g++ -v
Using built-in specs.
COLLECT_GCC=arm-none-eabi-g++
COLLECT_LTO_WRAPPER=/usr/local/cross/libexec/gcc/arm-none-eabi/4.7.2/lto-wrapper
Target: arm-none-eabi
Configured with: ../gcc-4.7.2/configure --target=arm-none-eabi
--prefix=/usr/local/cross --disable-nls --enable-languages=c,c++
--without-headers
Thread model: single
gcc version 4.7.2 (GCC)
% arm-none-eabi-gcc -O2 -save-temps -S bug.c good code
% arm-none-eabi-g++ -O2 -save-temps -S bug.c bad code
------------------------------------------------------------------
_Z3foov:
.fnstart
.LFB0:
@ Function supports interworking.
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 0, uses_anonymous_args = 0
@ link register save eliminated.
mov r3, #4096
@ 3 "bug.c" 1
swi #1
@ 0 "" 2
bx lr
------------------------------------------------------------------
The source explicitly asked for "r4" but g++ uses r3 instead.
