https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93037
Bug ID: 93037
Summary: Slow 'while' loop unrolling
Product: gcc
Version: 8.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: hehaochen at hotmail dot com
Target Milestone: ---
Created attachment 47538
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47538&action=edit
Adobe_C++Benchmarks
Compile and run 'loop unroll test' in Adobe C++ benchmark
(https://stlab.adobe.com/performance/). We find slowdown in GCC-8(docker) when
adding '-O3':
╔════════════════════════════════════════╦═════╦═════╦═════╦══════════╗
║ Total absolute execution time (sec.) ║ O1 ║ O2 ║ O3 ║ comments ║
╠═════════╦══════════════════════════════╬═════╬═════╬═════╬══════════╣
║ gcc-8 ║ int32_t for loop unrolling ║ 259 ║ 167 ║ 149 ║ ok ║
║ ╠══════════════════════════════╬═════╬═════╬═════╬══════════╣
║ ║ int32_t while loop unrolling ║ 257 ║ 164 ║ 204 ║ SLOW ║
╠═════════╬══════════════════════════════╬═════╬═════╬═════╬══════════╣
║ clang-6 ║ int32_t for loop unrolling ║ 326 ║ 206 ║ 181 ║ ok ║
║ ╠══════════════════════════════╬═════╬═════╬═════╬══════════╣
║ ║ int32_t while loop unrolling ║ 347 ║ 206 ║ 181 ║ ok ║
╚═════════╩══════════════════════════════╩═════╩═════╩═════╩══════════╝
The this performance issue do not occur in 'for' loop unrolling test or clang
either.
