[llvm] r256258 - [Support] Allow multiple paired calls to {start, stop}Timer()

[Davide Italiano via llvm-commits]

On Tue, Dec 22, 2015 at 9:36 AM, Vedant Kumar via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: vedantk
> Date: Tue Dec 22 11:36:17 2015
> New Revision: 256258
>
> URL: http://llvm.org/viewvc/llvm-project?rev=256258&view=rev
> Log:
> [Support] Allow multiple paired calls to {start,stop}Timer()
>
> Differential Revision: http://reviews.llvm.org/D15619
>
> Reviewed-by: rafael
>

I just noticed that there are cases in clang where we hit this
assertion (if timers are enabled in the frontend).

clang-3.9: /home/davide/work/checkout/llvm/lib/Support/Timer.cpp:139:
void llvm::Timer::startTimer(): Assertion `!Running && "Cannot start a
running timer"' failed.

I don't have a synthetic test case (at least not one I can share
easily) but this is what the stack trace looks like:

#9 0x00000000022b4252
clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef)
/home/davide/work/checkout/clang/lib/CodeGen/CodeGenAction.cpp:116:0
[...]
#61 0x00000000022b952c (anonymous
namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef)
/home/davide/work/checkout/clang/lib/CodeGen/ModuleBuilder.cpp:147:0
#62 0x00000000022b41eb
clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef)
/home/davide/work/checkout/clang/lib/CodeGen/CodeGenAction.cpp:120:0

We recurse on HandleTopLevelDecl() and inside HandleTopLevelDecl()
startTimer() is called, so, the second time we call the function the timer was
started already (but never stopped).
I don't think this should be handled by the clients of Timers but by
Timer itself.
My proposal is that of refcounting Timer so that every time we
increment the refcount in situation like this and only stop the
counter when the refcount goes to zero.

Thought(s) and or other opinion(s)?

Thanks!

--
Davide