https://bugs.llvm.org/show_bug.cgi?id=51157
Bug ID: 51157
Summary: Possible O(n^2) slowness in Global Value Numbering
Product: clang
Version: 10.0
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: -New Bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected]
Created attachment 25044
--> https://bugs.llvm.org/attachment.cgi?id=25044&action=edit
Examples and runtimes
This was noticed due to a much larger gcc performance bug
(https://github.com/verilator/verilator/issues/3072) but looking into this
there seems a possible clang issue also.
On clang version 10.0.0-4ubuntu1 the attached takes 37 seconds total.
clang++ -I. -c -Os -ftime-report -o /dev/null Vara___024root__114_0.cpp
In clang++, 33 of 37 seconds are in the "Global Value Numbering" stage. The
same splitting above in this stage takes 4.6, 2.9, and 3.9 seconds
(totalling 11.3). This thus seems a O(n^2) performance problem suspect.
This issue was originally reported using gcc 8.2.0 by Matheus Cavalcante
at https://github.com/verilator/verilator/issues/3072
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