https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65887
Bug ID: 65887
Summary: remove va_arg ap copies
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: vries at gcc dot gnu.org
[ Discussed here: https://gcc.gnu.org/ml/gcc-patches/2015-04/msg01262.html ]
When compiling gcc.target/x86_64/abi/callabi/vaarg-6.c, at original we have:
...
;; Function do_cpy2 (null)
{
char * e;
char * e;
e = VA_ARG_EXPR <argp>;
e = VA_ARG_EXPR <argp>;
if (e != b)
{
abort ();
}
}
...
and after gimplify we have:
...
do_cpy2 (char * argp)
{
char * argp.1;
char * argp.2;
char * b.3;
char * e;
argp.1 = argp;
e = VA_ARG (&argp.1, 0B);
argp = argp.1;
argp.2 = argp;
e = VA_ARG (&argp.2, 0B);
argp = argp.2;
b.3 = b;
if (e != b.3) goto <D.1373>; else goto <D.1374>;
<D.1373>:
abort ();
<D.1374>:
}
...
We'd like to generate:
...
e = VA_ARG (&argp, 0B);
...
instead of:
...
argp.1 = argp;
e = VA_ARG (&argp.1, 0B);
argp = argp.1;
...
The code generating the copyback 'argp = argp.1' is in gimplify_modify_expr.
