[PATCH] Passing down BinaryOperator flags to BinarySDNode + X86 optimization

[Owen Anderson]

Hi Marcello,

I haven’t looked at the code changes, but it appears that you accidentally ran clang-format over all of SelectionDAG.cpp as part of flag_nodes.patch.  Please separate your intended diff out from that.

—Owen

On May 29, 2014, at 7:44 PM, Marcello Maggioni <hayarms at gmail.com> wrote:

> Hello,
> 
> here is a proposed patch to pass down the BinaryOperator's "NoUnsignedWrap/NoSignedWrap and IsExact" flags down to the SDNodes so that backends can use them for additional optimizations.
> 
> The core of the patch is using the SubclassData field of SDNode for BinarySDNodes to store the flags information.
> SelectionDAGBuilder will then set the correct flag information the moment the Binary instruction is visited during construction.
> 
> In doing this I also refactored a little bit the getNode() method accepting two operands, extracting the main constant folding logic into a separate static function.
> 
> The patch implementing this is the file "flag_nodes.patch" attached.
> 
> In addition I implemented an optimization where an unneeded "test instruction" that was emitted from the X86 backend is not emitted anymore. This optimization uses this new feature.
> 
> This optimization is contained in the "x86_opt_wrap.patch" attached.
> 
> I also added a test case that exercises the optimization in the "factorial_test.patch"
> 
> The patch makes this snippet of code:
> 
> LBB0_1:                                 ## %while.body
>                                                ## =>This Inner Loop Header: Depth=1
>          imulq   %rdi, %rax
>          decq    %rdi
>          testq    %rdi, %rdi
>          jg      LBB0_1
> 
> 
> 
> become this:
> 
> 
> 
> LBB0_1:                                 ## %while.body
>                                                ## =>This Inner Loop Header: Depth=1
>          imulq   %rdi, %rax
>          decq    %rdi
>          jg      LBB0_1
> 
> if the NSW flag is set on the SDNode that represents the DEC instruction (presumably an ADD or a SUB node in this case).
> 
> If somebody could review this it would be awesome :)
> 
> Cheers,
> Marcello
> <factorial_test.patch><flag_nodes.patch><x86_opt_wrap.patch>_______________________________________________
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