https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89921
Bug ID: 89921
Summary: The dom pass does not respect size of an 'asm' when
duplicating BBs
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: vlad at ispras dot ru
Target Milestone: ---
// sizeof-asm-dom.c:
#define LARGE_ASM "\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
\
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
\
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
\
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
\
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
\
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
\
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
\
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
\
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
\
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
\
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
\
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
\
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
extern unsigned bar (void);
unsigned foo (unsigned v)
{
unsigned u;
unsigned o;
if (v > 10)
u = bar ();
asm (LARGE_ASM:"=g"(o)::); // a non-volatile asm.
if (v < 5)
return u;
return 0;
}
// EOF
gcc -O -fdump-tree-dom -c sizeof-asm-dom.c
grep asm sizeof-asm*dom2 | wc -l
This yields 2, i.e. the large asm has been duplicated.
My understanding (without having read the actual code of the dom pass) is that
the dom pass relies on a cost model to decide whether to perform the
duplication
(inserting a simple loop in place of the asm prevents it). Also, at some point
GCC computes an estimate of inline asm sizes based on the number of
instructions
they contain (as per "Size of an 'asm'" section of the manual). It seems, the
dom pass could use that information to avoid bloating the resulting code.
Is it just an unimplemented thing that needs fixing?
