Time Spent in Code Gen
The following charts show the time spent in the "back-end" of LLVM when compiling large projects (Clang+LLVM3.7 and Chrome). Please note: this page is based on the old repo compiler and the old clang. The latest LLVM+Clang performance results could be found in the page Compile-Faster-with-the-Program-Repository-and-ccache.
The llvm-prepo compiler work eliminates the back-end time for functions that are not changed by a user between compilations. These charts show the percentage compilation time reduction if we assume that the llvm-prepo passes themselves add no overhead; this corresponds to the ”speed of light” for the project.
The data in these charts was produced by capturing the output of the "-ftime-report" option, parsing the resulting files and categorizing each entry as "front-end" or "back-end". The build was performed 16 times and the mean timings taken for each source file.
The chart axes show:
- There is a point on the X axis for each source file.
- The position on the Y axis shows the ratio of time spent in clang (i.e. the “front-end”) to the time spent in LLVM (the “back-end”) performing optimization and code-generation.
The values are each individually sorted to produce a smooth curve. In other words, the position on the X axis does not reflect the compilation order for these source files.
Median percentage time in back-end:
| Debug | Release |
|---|---|
| 51.71 | 80.50 |
Median percentage time in back-end:
| Debug | Release |
|---|---|
| 60.30 | 80.62 |