[LLVMbugs] [Bug 19258] New: Vector extract placement causes 37% regression on fp-convert.

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19258

            Bug ID: 19258
           Summary: Vector extract placement causes 37% regression on
                    fp-convert.
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: atrick at apple.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

This LNT tester:
http://llvm.org/perf/db_default/v4/nts/graph?plot.0=34.161.2&highlight_run=23986

Showed a 37% regression on fp-convert after this checkin:

---
Author: atrick
Date: Mon Mar 24 21:18:47 2014
New Revision: 204699

URL: http://llvm.org/viewvc/llvm-project?rev=204699&view=rev
Log:
SLP vectorizer: Don't hoist vector extracts of phis.

Extracts coming from phis were being hoisted, while all others were
sunk to their uses. This was inconsistent and didn't seem to serve a
purpose. Changing all extracts to be sunk to uses is a prerequisite
for adding block frequency to the SLP vectorizer's cost model.
---

My own benchmarking on darwin/x86_64/sandybridge showed a slight improvement
after this checkin: (2.6 vs 2.8s).

If someone can reproduce the regression and show what caused it, we should
definitely teach the vectorizer to avoid the problem.

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20140326/a3ecc5d0/attachment.html>