Hello! > > ? ? ? ?* a/gcc/gcse.c (alloc_gcse_mem): Added code to run in PRE2. > > And this is necessary because...??? > > Why not just make it a separate pass in ix86-reorg that uses LCM? Look at > mode switching for an example.
I was also expecting that vzeroupper would be inserted in the same way as I387 mode switching instructions are inserted. To expand on Steven's suggestion, please see i386.h for OPTIMIZE_MODE_SWITCHING and following macros. At the moment, there are 4 separate entities that handle (four independent) insertions for mode switching for x87 for each mode of fistp or frndint instruction. Mode insertions will actually insert calculations of x87 control word (CW) at optimal points and push this new CW (together with old CW) to known stack slot to be consumed by fistp/frndint insn. You can add a new entitiy to enum ix86_entity (say, AVX_VZEROUPPER) and update OPTIMIZE_MODE_SWITCHING to perform mode insertion for AVX_VZEROUPPER entitiy when needed. Various modes for AVX_VZEROUPPER are defined in NUM_MODES_FOR_MODE_SWITCHING, mode transition in MODE_NEEDED and insn insertions in EMIT_MODE_SET. Please note that LCM handles all entities in parallel, so there is no need for extra passes. The real worker for mode switching is ix86_mode_needed, but don't forget that you can disable mode switching pass per-function when not needed through OPTIMIZE_MODE_SWITCHING macro. FYI: Existing x87 CW initialization insertion works this way: - fistp/frndint is inserted into insn stream and corresponding OPTIMIZE_MODE_SWITCHING flag is set. - inserted insn has i386_cw attribute that defines requested mode in which the insn operate. Based on this attribute, MODE_NEEDED handles mode transitions (please note that there are four independent entities) for each entitiy. - EMIT_MODE_SET emits CW initializations. These are further optimized by follow-up optimization passes, so two consecutive initializations at the same place are CSEd, etc. Uros.
