[PATCH] DAGCombiner: Fold pointless truncate, bitcast, buildvector series

[Arnold Schwaighofer]

Ping.


On Feb 15, 2013, at 4:24 PM, Arnold Schwaighofer <aschwaighofer at apple.com> wrote:

> Updated patch, moved the detailed explanation from the .ll test to llvm.org/bugs. We probably don't want this much text in an regression test.
> 
> 
> <0001-DAGCombiner-Fold-pointless-truncate-bitcast-buildvec.patch>
> 
> Thanks
> 
> On Feb 15, 2013, at 3:57 PM, Arnold Schwaighofer <aschwaighofer at apple.com> wrote:
> 
>> For example (2xi32) (truncate ((2xi64) bitcast (buildvector i32 a, i32 x, i32 b, i32 y)))
>> can be folded into a (2xi32) (buildvector i32 a, i32 b).
>> 
>> Such a DAG would cause uneccessary vdup instructions followed by vmovn
>> instructions on ARM.
>> 
>> We legalize to such a DAG on ARM NEON for a setcc olt, 2xf64, 2xf64. For example, in
>> the vectorized version of the code below.
>> 
>> double A[N];
>> double B[N];
>> 
>> void test_double_compare_to_double() {
>> int i;
>> for(i=0;i<N;i++)
>>   A[i] = (double)(A[i] < B[i]);
>> }
>> 
>> <0001-DAGCombiner-Fold-pointless-truncate-bitcast-buildvec.patch>


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