https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71625
Bug ID: 71625
Summary: missing strlen optimization on different array
initialization style
Product: gcc
Version: tree-ssa
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: renlin at gcc dot gnu.org
Target Milestone: ---
Hi,
The following two functions shall give the same result 3.
Currently, foo () can be optimized to return a constant.
bar (), however, contains function call to strlen, which is sub-optimal.
int foo ()
{
char array[] = "abc";
return __builtin_strlen (array);
}
int bar ()
{
char array[] = {'a', 'b', 'c', '\0'};
return __builtin_strlen (array);
}
Clang 3.8 produce optimal code-generation for both cases.
In addition, I have another case here:
int hallo ();
int dummy ()
{
char array[] = "abc";
return hallo () + __builtin_strlen (array);
}
the __builtin_strlen is not fold into a const as in foo () above. Presumably,
gcc is too conservative about what hallo () function can do. By adding a pure
attribute to hallo (), gcc will generate optimal code.
Clang 3.8 gives optimal code in this case as well.
