[PATCH][x86][part 2/2] Teach how to fold target specific dags for packed shifts by immedate count into build_vector.

[Andrea Di Biagio]

Thanks!
Committed revision 198113.

On Sat, Dec 28, 2013 at 4:24 AM, Nadav Rotem <nrotem at apple.com> wrote:
> Andrea, this LGTM. Please commit. Thanks!
>
> Sent from my iPhone
>
>> On Dec 27, 2013, at 17:18, Andrea Di Biagio <andrea.dibiagio at gmail.com> wrote:
>>
>> Hi,
>>
>> This patch implement the second part of a fix for a poor code-gen bug
>> originally discussed here:
>> http://thread.gmane.org/gmane.comp.compilers.llvm.cvs/169801
>>
>> The goal of this patch is to teach the x86 backend how to fold a
>> target specific dag node for packed vector shift by immedate count
>> (VSHLI/VSRLI/VSRAI) into a build_vector when the vector in input to
>> the shift is a build_vector of all constants or undef.
>>
>> Example:
>> ////
>> define <4 x i32> @test() {
>>  %1 = tail call <4 x i32> @llvm.x86.sse2.pslli.d(<4 x i32> <i32 1,
>> i32 2, i32 4, i32 8>, i32 3)
>>  ret <4 x i32> %1
>> }
>> ////
>>
>> Before this patch, llc (-mtriple x86_64-unknown-linux-gnu -mattr=sse2)
>> generated the following assembly sequence:
>>    movdqa    .LCPI0_0(%rip), %xmm0
>>    pslld    $3, %xmm0
>>
>> With this patch, the packed shift is correctly folded into a load from
>> constant pool:
>>    movaps    .LCPI0_0(%rip), %xmm0
>>
>> Target specific nodes for packed shifts by immediate count are in
>> general introduced by function 'getTargetVShiftByConstNode' (in
>> X86ISelLowering.cpp) when lowering shift operations, SSE/AVX immediate
>> shift intrinsics and (only in very few cases) SIGN_EXTEND_INREG dag
>> nodes.
>>
>> This patch adds extra rules for simplifying vector shifts inside
>> function 'getTargetVShiftByConstNode'.
>>
>> I added file test/CodeGen/X86/vec_shift5.ll to verify that packed
>> shifts by immediate are correctly folded into a build_vector when the
>> input vector to the shift dag node is a vector of constants or undefs.
>>
>> Please let me know if this patch is ok to submit.
>>
>>
>> Thanks,
>> Andrea Di Biagio
>> SN Systems - Sony Computer Entertainment Group
>> <patch.diff>