Bug 30099

Summary: misleading warning when && operator paired with a constant - is it operator precedence?
Product: cairo Reporter: Alexander Stohr <alexander.stohr>
Component: generalAssignee: Carl Worth <cworth>
Status: RESOLVED NOTABUG QA Contact: cairo-bugs mailing list <cairo-bugs>
Severity: normal    
Priority: medium CC: alexander.stohr
Version: 1.10.1   
Hardware: ARM   
OS: Linux (All)   
Whiteboard:
i915 platform: i915 features:

Description Alexander Stohr 2010-09-09 03:17:06 UTC 
gcc --version
gcc (GCC) 4.3.1
Copyright (C) 2008 Free Software Foundation, Inc.

found in package cairo-1.9.14 and file test/cairo-test.c with critical line 1597:
  if (ctx->thread == 0 && ! RUNNING_ON_VALGRIND)

build outputs:
"warning: logical '&&' with non-zero constant will always evaluate as true"

from the used setup the VALGRIND macro is assumed to have a true value.
(a code checker would probably suggest using round braces around the "==" part.
the used default project tuning of gcc does not raise a warning on operator precedence.)

whats the problem?
a) if you use && with a constant and something else
then your result will always either be false (const=false) or something else (const=true).
there is no case for the compiler seeing this as fixed to true.
b) maybe its unintended operator precedence that makes the case behave strangely
Comment 1 Chris Wilson 2010-09-09 03:22:51 UTC 
An overzealous warning; just warning that the (&& ! RUNNING_ON_VALGRIND) is redundant and compiled out.

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