ChuanqiXu added a comment. In D137059#3899339 <https://reviews.llvm.org/D137059#3899339>, @ben.boeckel wrote:
> There is another motivating factor for 1-phase: the build graph is far > simpler. With 2-phase, CMake will have to write out rules to perform: > > - source -> .bmi > - .bmi -> .withbmi.o > - source -> .o > > because we do not know if a BMI is needed or not. If it isn't we use the > latter. If it is, we use the former. Note that this also means we need 2 > different `.o` filenames (as neither `make` nor `ninja` doesn't support > multiple rules making the same output). This also means that the collator > needs to generate a response file for the linker to direct which `.o` file to > use for each TU based on the contents. > > Also with 2-phase, it is an open question of whether it actually helps with > distributed builds (or anywhere process execution and I/O are expensive > compared to some minimal work unit such as, say, Windows compiling from a > network drive). Since this is not a bright line, giving the option to say "I > know that split BMI is better for me in this instance" and "please combine > here" would be handy (depending on actual real-world perf results on > real-world projects). Yes, this is a chicken-and-egg cycle :) . In my mind, it is OK for CMake to support one-phase compilation model in the short term. And the fact that clang also supports the 2-phase compilation wouldn't affect CMake. Do I understand right? I mean, if the 2-phase compilation wouldn't affect CMake, CMake should be able to ignore it. My thought is that there are many more build systems in the world. And I know many of them would handle the dependency them self fully instead of translate the dependency to other build scripts like `make` and `ninja`. And I think it should be good for the compiler to remain different possibilities for different build systems (or tools). Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D137059/new/ https://reviews.llvm.org/D137059 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
