Re: [Intel-gfx] [PATCH] drm/i915: Zero initialize this_cpu in busywait_stop

[Chris Wilson]

Quoting Nathan Chancellor (2019-03-08 01:20:24)
> When building with -Wsometimes-uninitialized, Clang warns:
> 
> drivers/gpu/drm/i915/i915_request.c:1032:6: warning: variable 'this_cpu'
> is used uninitialized whenever '&&' condition is false
> [-Wsometimes-uninitialized]
> 
> time_after expands to use two typecheck with logical ANDs between them.
> typecheck evaluates to 1 but Clang clearly gets confused with the logic
> that as semantic analysis happens early in the pipeline. Fix this by
> just zero initializing this_cpu as it will always be properly
> initialized before the comparison below.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/415
> Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> ---
> 
> Alternatively, this can be solved by having the return value of
> local_clock_us(&this_cpu) be a local variable but this seems less
> controversial.

I'll just wait for clang to be fixed, as this severely undermines any
respect I have for its semantic analysis.
-Chris