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: [email protected]
Reporter: [email protected]
CC: [email protected]
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.
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