[Openmp-dev] variable 'new_value' is used uninitialized whenever 'if' condition is false

[Jack Howarth]

Jonathan,
      All of my builds on x86_64-apple-darwin14 are using the system
clang compilers from Xcode 6.3.2...

% clang -v
Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn)
Target: x86_64-apple-darwin14.4.0
Thread model: posix

I'll try a rebuild with LLVM clang 3.6.0 and see if there is any
differences in the warnings produced.
         Jack

On Wed, Jun 3, 2015 at 11:49 AM, Peyton, Jonathan L
<jonathan.l.peyton at intel.com> wrote:
> What compiler version is producing all these warnings?  Is it clang 3.7?
>
> -- Johnny
>
> -----Original Message-----
> From: Jack Howarth [mailto:howarth.mailing.lists at gmail.com]
> Sent: Tuesday, June 2, 2015 7:03 PM
> To: Peyton, Jonathan L; openmp-dev at dcs-maillist2.engr.illinois.edu
> Subject: variable 'new_value' is used uninitialized whenever 'if' condition is false
>
> Jonathan,
>       Are the warnings of the form...
>
> /sw/src/fink.build/llvm37-3.7.0-100/llvm-3.7.0.src/projects/openmp/runtime/src/kmp_atomic.c:2035:1:
> warning: variable 'new_value' is used uninitialized whenever 'if'
> condition is false
>       [-Wsometimes-uninitialized]
> MIN_MAX_COMPXCHG_CPT( fixed1,  max_cpt, char,        8, <,
> KMP_ARCH_X86 ) // __kmpc_atomic_fixed1_max_cpt ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /sw/src/fink.build/llvm37-3.7.0-100/llvm-3.7.0.src/projects/openmp/runtime/src/kmp_atomic.c:2028:9:
> note: expanded from macro 'MIN_MAX_COMPXCHG_CPT'
>         GOMP_MIN_MAX_CRITSECT_CPT(OP,GOMP_FLAG)                            \
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /sw/src/fink.build/llvm37-3.7.0-100/llvm-3.7.0.src/projects/openmp/runtime/src/kmp_atomic.c:1984:9:
> note: expanded from macro 'GOMP_MIN_MAX_CRITSECT_CPT'
>         MIN_MAX_CRITSECT_CPT( OP, 0 );                                     \
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /sw/src/fink.build/llvm37-3.7.0-100/llvm-3.7.0.src/projects/openmp/runtime/src/kmp_atomic.c:1968:10:
> note: expanded from macro 'MIN_MAX_CRITSECT_CPT'
>     if ( *lhs OP rhs ) {                 /* still need actions? */         \
>          ^~~~~~~~~~~
> /sw/src/fink.build/llvm37-3.7.0-100/llvm-3.7.0.src/projects/openmp/runtime/src/kmp_atomic.c:2035:1:
> note: uninitialized use occurs here
> MIN_MAX_COMPXCHG_CPT( fixed1,  max_cpt, char,        8, <,
> KMP_ARCH_X86 ) // __kmpc_atomic_fixed1_max_cpt ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /sw/src/fink.build/llvm37-3.7.0-100/llvm-3.7.0.src/projects/openmp/runtime/src/kmp_atomic.c:2028:9:
> note: expanded from macro 'MIN_MAX_COMPXCHG_CPT'
>         GOMP_MIN_MAX_CRITSECT_CPT(OP,GOMP_FLAG)                            \
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /sw/src/fink.build/llvm37-3.7.0-100/llvm-3.7.0.src/projects/openmp/runtime/src/kmp_atomic.c:1984:9:
> note: expanded from macro 'GOMP_MIN_MAX_CRITSECT_CPT'
>         MIN_MAX_CRITSECT_CPT( OP, 0 );                                     \
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /sw/src/fink.build/llvm37-3.7.0-100/llvm-3.7.0.src/projects/openmp/runtime/src/kmp_atomic.c:1977:12:
> note: expanded from macro 'MIN_MAX_CRITSECT_CPT'
>     return new_value;                                                      \
>            ^~~~~~~~~
> /sw/src/fink.build/llvm37-3.7.0-100/llvm-3.7.0.src/projects/openmp/runtime/src/kmp_atomic.c:2035:1:
> note: remove the 'if' if its condition is always true
> /sw/src/fink.build/llvm37-3.7.0-100/llvm-3.7.0.src/projects/openmp/runtime/src/kmp_atomic.c:2028:9:
> note: expanded from macro 'MIN_MAX_COMPXCHG_CPT'
>         GOMP_MIN_MAX_CRITSECT_CPT(OP,GOMP_FLAG)                            \
>         ^
> /sw/src/fink.build/llvm37-3.7.0-100/llvm-3.7.0.src/projects/openmp/runtime/src/kmp_atomic.c:1984:9:
> note: expanded from macro 'GOMP_MIN_MAX_CRITSECT_CPT'
>         MIN_MAX_CRITSECT_CPT( OP, 0 );                                     \
>         ^
> /sw/src/fink.build/llvm37-3.7.0-100/llvm-3.7.0.src/projects/openmp/runtime/src/kmp_atomic.c:1968:5:
> note: expanded from macro 'MIN_MAX_CRITSECT_CPT'
>     if ( *lhs OP rhs ) {                 /* still need actions? */         \
>     ^
> /sw/src/fink.build/llvm37-3.7.0-100/llvm-3.7.0.src/projects/openmp/runtime/src/kmp_atomic.c:2035:41:
> note: variable 'new_value' is declared here
> MIN_MAX_COMPXCHG_CPT( fixed1,  max_cpt, char,        8, <,
> KMP_ARCH_X86 ) // __kmpc_atomic_fixed1_max_cpt
>                                         ^
> /sw/src/fink.build/llvm37-3.7.0-100/llvm-3.7.0.src/projects/openmp/runtime/src/kmp_atomic.c:2026:5:
> note: expanded from macro 'MIN_MAX_COMPXCHG_CPT'
>     TYPE new_value, old_value;                                             \
>     ^
>
> significant? These seem to be generated from the macro definition...
>
> #define MIN_MAX_COMPXCHG_CPT(TYPE_ID,OP_ID,TYPE,BITS,OP,GOMP_FLAG)         \
> ATOMIC_BEGIN_CPT(TYPE_ID,OP_ID,TYPE,TYPE)                                  \
>     TYPE new_value, old_value;                                             \
>     if ( *lhs OP rhs ) {                                                   \
>         GOMP_MIN_MAX_CRITSECT_CPT(OP,GOMP_FLAG)                            \
>         MIN_MAX_CMPXCHG_CPT(TYPE,BITS,OP)                                  \
>     }                                                                      \
>     return *lhs;                                                           \
> }
>
>         Jack