Hello, The C++ front end pushes everything through the compiler queue after writing a PCH. This is pointless: After the PCH is written nothing the compiler does has any effect on it anymore.
This patch makes the C++ front end stop after writing the PCH, speeding up PCH creation The C front end has behaved this way since 2004 (http://gcc.gnu.org/ml/gcc-patches/2004-07/msg00738.html). Bootstrapped&tested on powerpc64-unknown-linux-gnu and x86_64-unknown-linux-gnu. OK for trunk? Ciao! Steven * decl2.c (cp_write_global_declarations): Return after writing a PCH. Index: decl2.c =================================================================== --- decl2.c (revision 194052) +++ decl2.c (working copy) @@ -3944,8 +3944,13 @@ cp_write_global_declarations (void) || !vec_safe_is_empty (decl_namespace_list)) return; + /* This is the point to write out a PCH if we're doing that. + In that case we do not want to do anything else. */ if (pch_file) - c_common_write_pch (); + { + c_common_write_pch (); + return; + } cgraph_process_same_body_aliases (); Compile time at -O2 (test = patched, orig = unpatched): $ for i in 1 2 3 ; do time ~/devel/build-test/gcc/xg++ -B../devel/build-test/gcc/ -w -O2 slow.h ; done ; ls -ltr real 0m8.577s user 0m8.037s sys 0m0.540s real 0m8.580s user 0m8.093s sys 0m0.484s real 0m8.595s user 0m8.093s sys 0m0.500s total 100440 -rw-r--r-- 1 stevenb stevenb 4017783 2012-12-02 21:16 slow.h -rw-r--r-- 1 stevenb stevenb 98722192 2012-12-02 21:20 slow.h.gch $ for i in 1 2 3 ; do time ~/devel/build-orig/gcc/xg++ -B../devel/build-orig/gcc/ -w -O2 slow.h ; done ; ls -ltr real 0m10.795s user 0m10.273s sys 0m0.520s real 0m10.876s user 0m10.365s sys 0m0.544s real 0m10.767s user 0m10.245s sys 0m0.520s total 100440 -rw-r--r-- 1 stevenb stevenb 4017783 2012-12-02 21:16 slow.h -rw-r--r-- 1 stevenb stevenb 98722192 2012-12-02 21:20 slow.h.gch
