Re: [PATCH] add more detail to -Wconversion and -Woverflow (PR 80731)

[Renlin Li <renlin dot li at foss dot arm dot com>]

Hi Martin,

I noticed the following failures after your change r248431.
FAIL: c-c++-common/Wfloat-conversion.c  -Wc++-compat   (test for warnings, line 42)
FAIL: c-c++-common/Wfloat-conversion.c  -Wc++-compat   (test for warnings, line 43)

It happens on arm target which is not a large_long_double target.
The patch here add the missing target selector. After the change, those test
won't checked in arm target.

Here I have a simple fix to it. Okay to commit?

gcc/testsuite/ChangeLog:

2017-06-02 Renlin Li <renlin.li@arm.com>

* c-c++-common/Wfloat-conversion.c: Add large_long_double target
selector to related line.



And there is another failure:
FAIL: gcc.dg/utf16-4.c  (test for warnings, line 15)

The warning message is slightly different from expected.
utf16-4.c:10:15: warning: character constant too long for its type
utf16-4.c:15:15: warning: conversion from 'long unsigned int' to 'char16_t {aka short 
unsigned int}' changes value from '410401' to '17185'

On 18/05/17 01:04, Martin Sebor wrote:
> While working on a new warning for unsafe conversion I noticed
> that the existing warnings that diagnose these kinds of problems
> are missing some useful detail. For example, given declarations
> of an integer Type and an integer Constant defined in some header,
> a C programmer who writes this declaration:
>
>    Type x = Constant;
>
> might see the following:
>
>    warning: overflow in implicit constant conversion [-Woverflow]
>
> To help the programmer better understand the problem and its impact
> it would be helpful to mention the types of the operands, and if
> available, also the values of the expressions.  For instance, like
> so:
>
>    warning: overflow in conversion from ‘int’ to ‘T {aka signed char}’ changes value from
> ‘123456789’ to ‘21’ [-Woverflow]
>
> The attached simple patch does just that.  In making the changes
> I tried to make the text of all the warnings follow the same
> consistent wording pattern without losing any essential information
> (e.g., I dropped "implicit" or "constant" because the implicit part
> is evident from the code (no cast) and explicit conversions aren't
> diagnosed, and because constant is apparent from the rest of the
> diagnostic that includes its value.
>
> Besides adding more detail and tweaking the wording the patch
> makes no functional changes (i.e., doesn't add new or remove
> existing warnings).
>
> Martin
>
> PS While adjusting the tests (a painstaking process) it occurred
> to me that these kinds of changes would be a whole lot easier if
> dg-warning directives simply checked for "-Woption-name" rather
> than some (often arbitrary) part of the warning text.  It might
> even be more accurate if the pattern happens to match the text
> of two or more warnings controlled by different options.
>
> It's of course important to also exercise the full text of
> the warnings, especially where additional detail is included
> (like in this patch), but that can be done in a small subset
> of tests.  All the others that just verify the presence of
> a warning controlled by a given option could use the simpler
> approach.
diff --git a/gcc/testsuite/c-c++-common/Wfloat-conversion.c b/gcc/testsuite/c-c++-common/Wfloat-conversion.c
index e9899bc..c33a2a6 100644
--- a/gcc/testsuite/c-c++-common/Wfloat-conversion.c
+++ b/gcc/testsuite/c-c++-common/Wfloat-conversion.c
@@ -39,8 +39,8 @@ void h (void)
   vfloat = vdouble; /* { dg-warning "conversion from .double. to .float. may change value" } */
   ffloat (vlongdouble); /* { dg-warning "conversion from .long double. to .float. may change value" } */
   vfloat = vlongdouble; /* { dg-warning "conversion from .long double. to .float. may change value" } */
-  fdouble (vlongdouble); /* { dg-warning "conversion from .long double. to .double. may change value" } */
-  vdouble = vlongdouble; /* { dg-warning "conversion from .long double. to .double. may change value" } */
+  fdouble (vlongdouble); /* { dg-warning "conversion from .long double. to .double. may change value" "" { target large_long_double } } */
+  vdouble = vlongdouble; /* { dg-warning "conversion from .long double. to .double. may change value" "" { target large_long_double } } */
 
   fsi (3.1f); /* { dg-warning "conversion from .float. to .int. changes value" } */
   si = 3.1f; /* { dg-warning "conversion from .float. to .int. changes value" } */