llvm dev - May 2014 - [LLVMdev] [PATCH] Passing down BinaryOperator flags to BinarySDNode + X86 optimization

Hello,

here is a proposed patch to pass down BinaryOperator the
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
BinarySDNode 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" in X86 where emitted that 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 of that represents the DEC instruction
(presumably an ADD or a SUB).

If somebody could review this it would be awesome :)

Cheers,
Marcello
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