Re: r271544 - [docs] Add a limitations section to SourceBasedCodeCoverage.rst

[Vedant Kumar via cfe-commits]

> On Jun 4, 2016, at 6:28 PM, Sean Silva  wrote:
> 
> 
> 
> On Thu, Jun 2, 2016 at 10:19 AM, Vedant Kumar via cfe-commits 
>  wrote:
> Author: vedantk
> Date: Thu Jun  2 12:19:45 2016
> New Revision: 271544
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=271544&view=rev
> Log:
> [docs] Add a limitations section to SourceBasedCodeCoverage.rst
> 
> Modified:
> cfe/trunk/docs/SourceBasedCodeCoverage.rst
> 
> Modified: cfe/trunk/docs/SourceBasedCodeCoverage.rst
> URL: 
> http://llvm.org/viewvc/llvm-project/cfe/trunk/docs/SourceBasedCodeCoverage.rst?rev=271544&r1=271543&r2=271544&view=diff
> ==
> --- cfe/trunk/docs/SourceBasedCodeCoverage.rst (original)
> +++ cfe/trunk/docs/SourceBasedCodeCoverage.rst Thu Jun  2 12:19:45 2016
> @@ -165,9 +165,9 @@ A few final notes:
>indexed profiles. To combine profiling data from multiple runs of a 
> program,
>try e.g:
> 
> -.. code-block:: console
> +  .. code-block:: console
> 
> -% llvm-profdata merge -sparse foo1.profraw foo2.profdata -o foo3.profdata
> +  % llvm-profdata merge -sparse foo1.profraw foo2.profdata -o 
> foo3.profdata
> 
>  Format compatibility guarantees
>  ===
> @@ -184,3 +184,20 @@ Format compatibility guarantees
>  * There is a third format in play: the format of the coverage mappings 
> emitted
>into instrumented binaries. Tools must retain **backwards** compatibility
>with these formats. These formats are not forwards-compatible.
> +
> +Drawbacks and limitations
> +=
> +
> +* Code coverage does not handle stack unwinding in the presence of uncaught
> +  exceptions precisely.
> 
> I think it's more accurate to say "thrown exceptions" (or just "exceptions") 
> instead of "uncaught exceptions". The latter could be interpreted as meaning 
> that if the exception is caught later (in a caller of f), then the result 
> might still be precise.

Fair point, I've dropped the "uncaught" modifier.


> Also setjmp/longjmp can affect things too, no?

Yes, I mentioned this in r271902. Feel free to change up the wording!

thanks
vedant


> 
> -- Sean Silva
>  
> Consider the following function:
> +
> +  .. code-block:: cpp
> +
> +  int f() {
> +may_throw();
> +return 0;
> +  }
> +
> +  If the function ``may_throw()`` propagates an exception into ``f``, the 
> code
> +  coverage tool may mark the ``return`` statement as executed even though it 
> is
> +  not.
> 
> 
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Re: r271544 - [docs] Add a limitations section to SourceBasedCodeCoverage.rst

[Sean Silva via cfe-commits]

On Thu, Jun 2, 2016 at 10:19 AM, Vedant Kumar via cfe-commits <
cfe-commits@lists.llvm.org> wrote:

> Author: vedantk
> Date: Thu Jun  2 12:19:45 2016
> New Revision: 271544
>
> URL: http://llvm.org/viewvc/llvm-project?rev=271544&view=rev
> Log:
> [docs] Add a limitations section to SourceBasedCodeCoverage.rst
>
> Modified:
> cfe/trunk/docs/SourceBasedCodeCoverage.rst
>
> Modified: cfe/trunk/docs/SourceBasedCodeCoverage.rst
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/docs/SourceBasedCodeCoverage.rst?rev=271544&r1=271543&r2=271544&view=diff
>
> ==
> --- cfe/trunk/docs/SourceBasedCodeCoverage.rst (original)
> +++ cfe/trunk/docs/SourceBasedCodeCoverage.rst Thu Jun  2 12:19:45 2016
> @@ -165,9 +165,9 @@ A few final notes:
>indexed profiles. To combine profiling data from multiple runs of a
> program,
>try e.g:
>
> -.. code-block:: console
> +  .. code-block:: console
>
> -% llvm-profdata merge -sparse foo1.profraw foo2.profdata -o
> foo3.profdata
> +  % llvm-profdata merge -sparse foo1.profraw foo2.profdata -o
> foo3.profdata
>
>  Format compatibility guarantees
>  ===
> @@ -184,3 +184,20 @@ Format compatibility guarantees
>  * There is a third format in play: the format of the coverage mappings
> emitted
>into instrumented binaries. Tools must retain **backwards**
> compatibility
>with these formats. These formats are not forwards-compatible.
> +
> +Drawbacks and limitations
> +=
> +
> +* Code coverage does not handle stack unwinding in the presence of
> uncaught
> +  exceptions precisely.


I think it's more accurate to say "thrown exceptions" (or just
"exceptions") instead of "uncaught exceptions". The latter could be
interpreted as meaning that if the exception is caught later (in a caller
of f), then the result might still be precise.

Also setjmp/longjmp can affect things too, no?

-- Sean Silva


> Consider the following function:
> +
> +  .. code-block:: cpp
> +
> +  int f() {
> +may_throw();
> +return 0;
> +  }
> +
> +  If the function ``may_throw()`` propagates an exception into ``f``, the
> code
> +  coverage tool may mark the ``return`` statement as executed even though
> it is
> +  not.
>
>
> ___
> cfe-commits mailing list
> cfe-commits@lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
>
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r271544 - [docs] Add a limitations section to SourceBasedCodeCoverage.rst

[Vedant Kumar via cfe-commits]

Author: vedantk
Date: Thu Jun  2 12:19:45 2016
New Revision: 271544

URL: http://llvm.org/viewvc/llvm-project?rev=271544&view=rev
Log:
[docs] Add a limitations section to SourceBasedCodeCoverage.rst

Modified:
cfe/trunk/docs/SourceBasedCodeCoverage.rst

Modified: cfe/trunk/docs/SourceBasedCodeCoverage.rst
URL: 
http://llvm.org/viewvc/llvm-project/cfe/trunk/docs/SourceBasedCodeCoverage.rst?rev=271544&r1=271543&r2=271544&view=diff
==
--- cfe/trunk/docs/SourceBasedCodeCoverage.rst (original)
+++ cfe/trunk/docs/SourceBasedCodeCoverage.rst Thu Jun  2 12:19:45 2016
@@ -165,9 +165,9 @@ A few final notes:
   indexed profiles. To combine profiling data from multiple runs of a program,
   try e.g:
 
-.. code-block:: console
+  .. code-block:: console
 
-% llvm-profdata merge -sparse foo1.profraw foo2.profdata -o foo3.profdata
+  % llvm-profdata merge -sparse foo1.profraw foo2.profdata -o foo3.profdata
 
 Format compatibility guarantees
 ===
@@ -184,3 +184,20 @@ Format compatibility guarantees
 * There is a third format in play: the format of the coverage mappings emitted
   into instrumented binaries. Tools must retain **backwards** compatibility
   with these formats. These formats are not forwards-compatible.
+
+Drawbacks and limitations
+=
+
+* Code coverage does not handle stack unwinding in the presence of uncaught
+  exceptions precisely. Consider the following function:
+
+  .. code-block:: cpp
+
+  int f() {
+may_throw();
+return 0;
+  }
+
+  If the function ``may_throw()`` propagates an exception into ``f``, the code
+  coverage tool may mark the ``return`` statement as executed even though it is
+  not.


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