https://llvm.org/bugs/show_bug.cgi?id=24667
Bug ID: 24667
Summary: [Regression] Quadratic module build time due to
Preprocessor::LeaveSubmodule
Product: clang
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Modules
Assignee: unassignedclangb...@nondot.org
Reporter: chisophu...@gmail.com
CC: dgre...@apple.com, llvm-bugs@lists.llvm.org
Classification: Unclassified
Created attachment 14809
--> https://llvm.org/bugs/attachment.cgi?id=14809&action=edit
Test script exhibiting quadratic module build time with ToT.
Consider:
module foo {
header "foo1.h"
header "foo2.h"
......
}
foo<n>.h:
#pragma once
#define FOO_<n>
Preprocessor::LeaveSubmodule does O(# macros in submodule) work every time it
leaves a header. This results in quadratic build times, a regression from clang
3.6
The attached script shows the following times for different values of N with
ToT:
(N) (time)
128 0.0208690166473
256 0.0294139385223
512 0.0603349208832
1024 0.158221006393
2048 0.521872997284
4096 1.93269181252
8192 7.92222499847
Same thing but for clang 3.6:
128 0.0171859264374
256 0.0209867954254
512 0.0306701660156
1024 0.0452530384064
2048 0.0781750679016
4096 0.141057014465
8192 0.270556926727
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