[PATCH] R600: Don't unconditionally unroll loops with private memory accesses

[Matt Arsenault]

On 02/14/2014 07:54 AM, Tom Stellard wrote:
> From: Tom Stellard <thomas.stellard at amd.com>
>
> This causes the size of the scrypt kernel to explode and eats all the
> memory on some systems.
> ---
>   lib/Target/R600/AMDGPUTargetTransformInfo.cpp | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/lib/Target/R600/AMDGPUTargetTransformInfo.cpp b/lib/Target/R600/AMDGPUTargetTransformInfo.cpp
> index 7f37658..9cdfec5 100644
> --- a/lib/Target/R600/AMDGPUTargetTransformInfo.cpp
> +++ b/lib/Target/R600/AMDGPUTargetTransformInfo.cpp
> @@ -110,9 +110,13 @@ void AMDGPUTTI::getUnrollingPreferences(Loop *L,
>           // instructions that make it through to the code generator.  allocas
>           // require us to use indirect addressing, which is slow and prone to
>           // compiler bugs.  If this loop does an address calculation on an
> -        // alloca ptr, then we want to unconditionally unroll the loop.  In most
> -        // cases, this will make it possible for SROA to eliminate these allocas.
> -        UP.Threshold = UINT_MAX;
> +        // alloca ptr, then we want to use a higher than normal loop unroll
> +	// threshold.  This will give SROA a better chance to eliminate these
> +	// allocas.
> +	//
> +	// Don't use the maximum allowed value here as it will make some
> +	// programs way too big.
> +        UP.Threshold = 500;
>         }
>       }
>     }
Is there a specific reason for the value of 500?