[llvm-dev] BSWAP matching in codegen

[Jim Lewis via llvm-dev]

Thanks, that helps enormously! The issue is that the match is supposed to support both cascade and tree OR patterns, but there appears to be a problem with the tree matching. Both test1 and test6 in the ARM tests exercise the cascade pattern, and I remember now our fix is confined to the tree case.

I hesitate to claim now that there’s no coverage for the tree pattern, but it is failing to match the patterns we use in our tests, one of which looks like this:

define i32 @test_tree(i32 %x) {
     %byte0 = and i32 %x, 255        ; 0x000000ff
  %byte1 = and i32 %x, 65280      ; 0x0000ff00
  %byte2 = and i32 %x, 16711680   ; 0x00ff0000
  %byte3 = and i32 %x, 4278190080 ; 0xff000000

  %tmp0 = shl  i32 %byte0, 8
  %tmp1 = lshr i32 %byte1, 8
  %tmp2 = shl  i32 %byte2, 8
  %tmp3 = lshr i32 %byte3, 8

  %or0 = or i32 %tmp0, %tmp1
  %or1 = or i32 %tmp2, %tmp3

  %result = or i32 %or0, %or1
  ret i32 %result
}

I’m still investigating exactly how it’s failing on this one; let me know if I’m missing something else here.

Jim

On 12/8/16, 2:45 PM, "Friedman, Eli" <efriedma at codeaurora.org<mailto:efriedma at codeaurora.org>> wrote:

On 12/8/2016 12:05 PM, Jim Lewis wrote:
>> Are you sure there isn't any test coverage?  As far as I can tell, the tests from https://reviews.llvm.org/rL133503 are still in the tree.

I looked at those, but none of them include the full pattern that decomposes into bswap and rol. I debugged through the X86 bswap.ll test and verified none of those cases make it through MatchBSwapHWord (they get handled in MatchBSwapHWordLow instead).

The x86 tests don't, but the ARM tests do: see, for example, test6 in test/CodeGen/ARM/rev.ll.  If you compile that for x86, you get the expected bswap+rol.

-Eli



--

Employee of Qualcomm Innovation Center, Inc.

Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project


-- The information contained in this message is intended only for the recipient, and may be a confidential attorney-client communication or may otherwise be privileged and confidential and protected from disclosure. If the reader of this message is not the intended recipient, or an employee or agent responsible for delivering this message to the intended recipient, any dissemination or copying of this communication is strictly prohibited. If you have received this communication in error, please immediately notify us by replying to the message and then deleting it from your computer. Please note that KnuEdge, Inc. reserves the right to monitor and review the content of any electronic message or information sent to or from KnuEdge employee e-mail addresses without informing the sender or recipient of the message.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20161209/ca3f7b28/attachment-0001.html>