On Fri, Jan 29, 2016 at 11:38 AM, Alan Modra <amo...@gmail.com> wrote: > Since 4c4a180d, LTO has turned off flag_pic when linking a fixed > position executable. This results in flag_pic being zero in > rs6000_file_start, and no definition of ".LCTOC1". > > However, when we get to actually emitting code, flag_pic may be on > again, and references made to ".LCTOC1". How flag_pic comes to be > enabled again is quite a story. It goes like this.. If a function is > compiled with -fPIC then sysv4.h SUBTARGET_OVERRIDE_OPTIONS will set > TARGET_RELOCATABLE. Conversely, if TARGET_RELOCATABLE is set and > flag_pic is zero, then SUBTARGET_OVERRIDE_OPTIONS will set flag_pic=2. > It also happens that TARGET_RELOCATABLE is a bit in rs6000_isa_flags, > which is handled by rs6000_function_specific_save and > rs6000_function_specific_restore. That last fact means lto streaming > keeps track of the state of TARGET_RELOCATABLE for functions, and when > options are restored for a given function we'll set flag_pic=2 if the > function was originally compiled with -fPIC. That's bad because it > defeats the purpose of the 4c4a180d lto change, resulting in worse > optimization of ppc32 executables. What's more, we don't seem to turn > off flag_pic once it is on. > > We should really untangle the flag_pic/TARGET_RELOCATABLE mess, but > that change is probably a little dangerous for stage4. Instead, this > patch removes the toc symbol initialization from file_start and does > so when the first item is emitted to the toc, or after the function > epilogue in the cases where we emit code to initialize a toc pointer > but don't actually use it (-O0 mostly, I think). > > Bootstrapped and regression tested powerpc64-linux biarch with all > languages enabled. OK to apply? > > PR target/68662 > * config/rs6000/rs6000.c (need_toc_init): New var, set it > whenever toc_label_name used. > (rs6000_file_start): Don't set up toc section here, > (rs6000_output_function_epilogue): do so here instead, > (rs6000_xcoff_file_start): and here. > * config/rs6000/rs6000.md (load_toc_aix_si): Set need_toc_init. > (load_toc_aix_di): Likewise.
I'm worried about how this is going to interact with AIX. AIX assembler is single pass and this patch moves the initialization from the beginning of the file to the end of the file, which means there will be references to a label whose definition is delayed until the end. - David
