Keep history of macro definitions and #undefs
Summary:
Summary: Keep history of macro definitions and #undefs with corresponding source locations, so that we can later find out all macros active in a specified source location. We don't save the history in PCH (no need currently). Memory overhead is about sizeof(void*)*3*<number of macro definitions and #undefs>+<in-memory size of all #undef'd macros>
I've run a test on a file composed of 109 .h files from boost 1.49 on x86-64 linux.
Stats before this patch:
*** Preprocessor Stats:
73222 directives found:
19171 #define.
4345 #undef.
#include/#include_next/#import:
5233 source files entered.
27 max include stack depth
19210 #if/#ifndef/#ifdef.
2384 #else/#elif.
6891 #endif.
408 #pragma.
14466 #if/#ifndef#ifdef regions skipped
80023/451669/1270 obj/fn/builtin macros expanded, 85724 on the fast path.
127145 token paste (##) operations performed, 11008 on the fast path.
Preprocessor Memory: 5874615B total
BumpPtr: 4399104
Macro Expanded Tokens: 417768
Predefines Buffer: 8135
Macros: 1048576
#pragma push_macro Info: 0
Poison Reasons: 1024
Comment Handlers: 8
Stats with this patch:
...
Preprocessor Memory: 7541687B total
BumpPtr: 6066176
Macro Expanded Tokens: 417768
Predefines Buffer: 8135
Macros: 1048576
#pragma push_macro Info: 0
Poison Reasons: 1024
Comment Handlers: 8
In my test increase in memory usage is about 1.7Mb, which is ~28% of initial preprocessor's memory usage and about 0.8% of clang's total VMM allocation.
As for CPU overhead, it should only be noticeable when iterating over all macros, and should mostly consist of couple extra dereferences and one comparison per macro + skipping of #undef'd macros. It's less trivial to measure, though, as the preprocessor consumes a very small fraction of compilation time.
Reviewers: doug.gregor, klimek, rsmith, djasper
Reviewed By: doug.gregor
CC: cfe-commits, chandlerc
Differential Revision: http://llvm-reviews.chandlerc.com/D28
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@162810 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed