Hi @ll, I am wondering about the use of !isBeforeLegalize in PerformSELECTCombine in the X86 backend. This defers all VSELECT related DAG combines until after the Legalizer has run. If the IR has already only legal types the second round of DAG combines is skipped and no VSELECT specified optimizations are performed at all. Is there a reason we don’t run the X86 DAG combiner before Type Legalization? Thanks Cheers, Juergen
On Mon, Aug 19, 2013 at 3:34 PM, Juergen Ributzka <juergen at apple.com> wrote:> Hi @ll, > > I am wondering about the use of !isBeforeLegalize in PerformSELECTCombine > in the X86 backend. This defers all VSELECT related DAG combines until > after the Legalizer has run. If the IR has already only legal types the > second round of DAG combines is skipped and no VSELECT specified > optimizations are performed at all. > > Is there a reason we don’t run the X86 DAG combiner before Type > Legalization?I think the code in question is using isBeforeLegalize as a shortcut for "are all the operand and result types legal". -Eli -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130819/b38d29df/attachment.html>
I see. We still can use that shortcut to catch the simple case after type legalization, but we could also do a more elaborate type check before type legalization to enable it? On Aug 19, 2013, at 4:13 PM, Eli Friedman <eli.friedman at gmail.com> wrote:> On Mon, Aug 19, 2013 at 3:34 PM, Juergen Ributzka <juergen at apple.com> wrote: > Hi @ll, > > I am wondering about the use of !isBeforeLegalize in PerformSELECTCombine in the X86 backend. This defers all VSELECT related DAG combines until after the Legalizer has run. If the IR has already only legal types the second round of DAG combines is skipped and no VSELECT specified optimizations are performed at all. > > Is there a reason we don’t run the X86 DAG combiner before Type Legalization? > > I think the code in question is using isBeforeLegalize as a shortcut for "are all the operand and result types legal". > > -Eli-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130819/e62c2f68/attachment.html>