Thanks for the reviews. I have incorporated all but one (See below; its the change in the warning's
brief summary in common.opt) in the patch.

In this patch,

1. -Wmissing-profile is a warning by default and is ON by default with
    -fprofile-use
2. Attached pr86957-missing-profile-diagnostic-2 shows the warning messages
3. Added a testcase for warning in the case of missing profile feedback data
    file for a compilation unit

Thanks

gcc/ChangeLog:

2018-09-14  "Indu Bhagat"<indu.bhagat@oracle.com>

         * common.opt: New warning option -Wmissing-profile.
         * coverage.c (get_coverage_counts): Add warning for missing .gcda file.
         * doc/invoke.texi: Document -Wmissing-profile.

gcc/testsuite/ChangeLog:

2018-09-14  "Indu Bhagat"<indu.bhagat@oracle.com>

         * gcc.dg/Wmissing-profile.c: New test.


On 09/11/2018 02:21 AM, Martin Liška wrote:
>> diff --git a/gcc/common.opt b/gcc/common.opt
>> index ebc3ef4..d93ddca 100644
>> --- a/gcc/common.opt
>> +++ b/gcc/common.opt
>> @@ -811,6 +811,10 @@ Wcoverage-mismatch
>>   Common Var(warn_coverage_mismatch) Init(1) Warning
>>   Warn in case profiles in -fprofile-use do not match.
>>   
>> +Wmissing-profile
>> +Common Var(warn_missing_profile) Init(1) Warning
>> +Warn in case profiles in -fprofile-use do not exist.
> Maybe 'Want about missing profile for a function in -fprofile-use build.' ?
>

Since, Wmissing-profile also warns when feedback data file is missing for a compilation unit, the
suggested text above will be more restrictive. So I did not change.