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optimization/6854: missed optimization with attribute const & pure
- From: ghazi at caip dot rutgers dot edu
- To: gcc-gnats at gcc dot gnu dot org
- Date: 29 May 2002 01:55:38 -0000
- Subject: optimization/6854: missed optimization with attribute const & pure
- Reply-to: ghazi at caip dot rutgers dot edu
>Number: 6854
>Category: optimization
>Synopsis: missed optimization with attribute const & pure
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: pessimizes-code
>Submitter-Id: net
>Arrival-Date: Tue May 28 18:56:00 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator: Kaveh Ghazi
>Release: gcc version 3.2 20020527 (experimental)
>Organization:
>Environment:
Probably all, but known to occur on at least:
sparc-sun-solaris2.7
mips-sgi-irix6.2
and judging by the testresults:
http://gcc.gnu.org/ml/gcc-testresults/2002-05/msg00989.html
http://gcc.gnu.org/ml/gcc-testresults/2002-05/msg00980.html
http://gcc.gnu.org/ml/gcc-testresults/2002-05/msg00967.html
it also occurs on i686, ia64 and alpha.
>Description:
Using the current 3.2 trunk, gcc fails to optimize several sections in the testcase attached. It's also installed as:
gcc.c-torture/execute/pure-1.c
The testcase is designed to emit link errors when the optimizations fail to occur. When I compile it (e.g. with -O/-O2) I get:
Undefined first referenced
symbol in file
link_error4 /var/tmp//cci2nHoc.o
link_error5 /var/tmp//cci2nHoc.o
link_error6 /var/tmp//cci2nHoc.o
link_error7 /var/tmp//cci2nHoc.o
As noted by the particular optimizing failures, this appears to relate to the inability of gcc to detect as pure or const a function which contain calls to other const/pure functions.
NOTE: gcc-3.1.1-pre and 3.0.3 fail on 2, 4 and 6 so the appearance of link_error 5 & 7 represents a regression. While the disappearance of 2 is a (slight) improvement.
See: http://gcc.gnu.org/ml/gcc-patches/2002-05/msg02137.html
>How-To-Repeat:
Compile the attached testcase with -O
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted:
----gnatsweb-attachment----
Content-Type: text/plain; name="pure-1.c"
Content-Disposition: inline; filename="pure-1.c"
/* Origin: Kaveh Ghazi <ghazi@caip.rutgers.edu> 2002-05-27. */
/* Use a different function for each test so the link failures
indicate which one is broken. */
extern void link_error0 (void);
extern void link_error1 (void);
extern void link_error2 (void);
extern void link_error3 (void);
extern void link_error4 (void);
extern void link_error5 (void);
extern void link_error6 (void);
extern void link_error7 (void);
extern int i;
extern int func0 (int) __attribute__ ((__pure__));
extern int func1 (int) __attribute__ ((__const__));
/* GCC should automatically detect attributes for these functions.
Don't allow -O3 to inline them. */
#define ANI __attribute__ ((__noinline__))
static int ANI func2 (int a) { return i + a; } /* pure */
static int ANI func3 (int a) { return a * 3; } /* const */
static int ANI func4 (int a) { return func0(a) + a; } /* pure */
static int ANI func5 (int a) { return a + func1(a); } /* const */
static int ANI func6 (int a) { return func2(a) + a; } /* pure */
static int ANI func7 (int a) { return a + func3(a); } /* const */
int main ()
{
int i[10], r;
i[0] = 0;
r = func0(0);
if (i[0])
link_error0();
i[1] = 0;
r = func1(0);
if (i[1])
link_error1();
i[2] = 0;
r = func2(0);
if (i[2])
link_error2();
i[3] = 0;
r = func3(0);
if (i[3])
link_error3();
i[4] = 0;
r = func4(0);
if (i[4])
link_error4();
i[5] = 0;
r = func5(0);
if (i[5])
link_error5();
i[6] = 0;
r = func6(0);
if (i[6])
link_error6();
i[7] = 0;
r = func7(0);
if (i[7])
link_error7();
return r;
}
int func0 (int a) { return a - i; } /* pure */
int func1 (int a) { return a - a; } /* const */
int i = 2;
#ifndef __OPTIMIZE__
/* Avoid link failures when not optimizing. */
void link_error0() {}
void link_error1() {}
void link_error2() {}
void link_error3() {}
void link_error4() {}
void link_error5() {}
void link_error6() {}
void link_error7() {}
#endif /* ! __OPTIMIZE__ */