https://llvm.org/bugs/show_bug.cgi?id=26837
Bug ID: 26837
Summary: Availability of SSE detrimental to code performance
Product: libraries
Version: 3.8
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: tulip...@gmail.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
The following Rust playpen snippet (possible to see IR or ASM interactively)
http://is.gd/FrGoDm
produces the following benchmark results, depending on codegen options:
Pentium2
test folds1 ... bench: 736 ns/iter (+/- 5)
test folds2 ... bench: 731 ns/iter (+/- 1)
Pentium3 (or +sse)
test folds1 ... bench: 932 ns/iter (+/- 2)
test folds2 ... bench: 933 ns/iter (+/- 8)
Pentium4 (or +sse2)
running 2 tests
test folds1 ... bench: 249 ns/iter (+/- 1)
test folds2 ... bench: 733 ns/iter (+/- 6)
It seems availability of SSE2 enables successful vectorisation, whereas of SSE
makes the code slower. The latter shouldn't happen.
--
You are receiving this mail because:
You are on the CC list for the bug.
_______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
