Most of the time in whole-program compilers such at Manticore and MLton (> 60%, though it depends on the particular program) is spent in the combination of pars

Most of the time in whole-program compilers such at Manticore and MLton (> 60%, though it depends on the particular program) is spent in the combination of parsing the input source files and running GCC over the generated assembly to produce the binary. Many compilers (including ours) did not keep around that extra information because even in 2007 (when we started) RAM was a bit scarce. The cost associated with keeping that info around between phases is primarily in the extra working set hit and the resulting GC and especially memory paging issues. Given that it's not unreasonable to expect people to have > 1GB of available physical RAM for the compilation process these days, that's something we should consider changing. Though at this point threading that info through the compiler is probably a couple weeks of dedicated effort to get working correctly.