[Bug c/39088] New: Warning about potential use of uninitialized variable

[av1474 at comtv dot ru]

Following emits a warning about potential use of uninitialized variable,
even though the variable initialization and it's use are guarded by the
same predicate.

int f (void);

int g (int a)
{
int b;

if (a) b = f ();
asm volatile (#);
if (a) return b;
return 1;
}

$ gcc -O -Wuninitialized -c repro.c
repro.c: In function 'g':
repro.c:5: warning: 'b' may be used uninitialized in this function

This happens with gcc 4.3.0 and 4.3.1


-- 
   Summary: Warning about potential use of uninitialized variable
   Product: gcc
   Version: unknown
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: av1474 at comtv dot ru
 GCC build triplet: powerpc-unknown-linux-gnu
  GCC host triplet: powerpc-unknown-linux-gnu
GCC target triplet: powerpc-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39088

[Bug middle-end/36296] bogus uninitialized warning (loop representation, VRP missed-optimization)

[av1474 at comtv dot ru]

--- Comment #14 from av1474 at comtv dot ru  2009-02-02 23:44 ---
(In reply to comment #8)
 Please provide a preprocessed reduced testcase as similar to the original as
 possible. 
 
 I think this is not only predicated PHI but our representation of loops may
 also have something to do.
 

I'm not sure whether following warrants a new bug entry so doing it here,
sorry,
if it was inappropriate.

Following code, triggers:
 repro.c:5: warning: 'b' may be used uninitialized in this function
with 4.3.0 and 4.3.1 on PowerPC when invoked like this:

gcc -c -O -Wuninitialized repro.c

int f (void);

int g (int a)
{
int b;

if (a) b = f ();
asm volatile (#);
if (a) return b;
return 1;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36296