On Sun, Dec 14, 2014 at 3:08 PM, H.J. Lu <hjl.to...@gmail.com> wrote:
>> >>>> The enclosed testcase fails on x86 when compiled with -Os since we pass >> >>>> a byte parameter with a byte load in caller and read it as an int in >> >>>> callee. The reason it only shows up with -Os is x86 backend encodes >> >>>> a byte load with an int load if -O isn't used. When a byte load is >> >>>> used, the upper 24 bits of the register have random value for none >> >>>> WORD_REGISTER_OPERATIONS targets. >> >>>> >> >>>> It happens because setup_incoming_promotions in combine.c has >> >>>> >> >>>> /* The mode and signedness of the argument before any promotions >> >>>> happen >> >>>> (equal to the mode of the pseudo holding it at that stage). */ >> >>>> mode1 = TYPE_MODE (TREE_TYPE (arg)); >> >>>> uns1 = TYPE_UNSIGNED (TREE_TYPE (arg)); >> >>>> >> >>>> /* The mode and signedness of the argument after any source >> >>>> language and >> >>>> TARGET_PROMOTE_PROTOTYPES-driven promotions. */ >> >>>> mode2 = TYPE_MODE (DECL_ARG_TYPE (arg)); >> >>>> uns3 = TYPE_UNSIGNED (DECL_ARG_TYPE (arg)); >> >>>> >> >>>> /* The mode and signedness of the argument as it is actually >> >>>> passed, >> >>>> after any TARGET_PROMOTE_FUNCTION_ARGS-driven ABI promotions. >> >>>> */ >> >>>> mode3 = promote_function_mode (DECL_ARG_TYPE (arg), mode2, &uns3, >> >>>> TREE_TYPE (cfun->decl), 0); >> >>>> >> >>>> while they are actually passed in register by assign_parm_setup_reg in >> >>>> function.c: >> >>>> >> >>>> /* Store the parm in a pseudoregister during the function, but we may >> >>>> need to do it in a wider mode. Using 2 here makes the result >> >>>> consistent with promote_decl_mode and thus expand_expr_real_1. */ >> >>>> promoted_nominal_mode >> >>>> = promote_function_mode (data->nominal_type, data->nominal_mode, >> >>>> &unsignedp, >> >>>> TREE_TYPE (current_function_decl), 2); >> >>>> >> >>>> where nominal_type and nominal_mode are set up with TREE_TYPE (parm) >> >>>> and TYPE_MODE (nominal_type). TREE_TYPE here is >> >>> >> >>> I think the bug is here, not in combine.c. Can you try going back in >> >>> history >> >>> for both snippets and see if they matched at some point? >> >>> >> >> >> >> The bug was introduced by >> >> >> >> https://gcc.gnu.org/ml/gcc-cvs/2007-09/msg00613.html >> >> >> >> commit 5d93234932c3d8617ce92b77b7013ef6bede9508 >> >> Author: shinwell <shinwell@138bc75d-0d04-0410-961f-82ee72b054a4> >> >> Date: Thu Sep 20 11:01:18 2007 +0000 >> >> >> >> gcc/ >> >> * combine.c: Include cgraph.h. >> >> (setup_incoming_promotions): Rework to allow more aggressive >> >> elimination of sign extensions when all call sites of the >> >> current function are known to lie within the current unit. >> >> >> >> >> >> git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@128618 >> >> 138bc75d-0d04-0410-961f-82ee72b054a4 >> >> >> >> Before this commit, combine.c has >> >> >> >> enum machine_mode mode = TYPE_MODE (TREE_TYPE (arg)); >> >> int uns = TYPE_UNSIGNED (TREE_TYPE (arg)); >> >> >> >> mode = promote_mode (TREE_TYPE (arg), mode, &uns, 1); >> >> if (mode == GET_MODE (reg) && mode != DECL_MODE (arg)) >> >> { >> >> rtx x; >> >> x = gen_rtx_CLOBBER (DECL_MODE (arg), const0_rtx); >> >> x = gen_rtx_fmt_e ((uns ? ZERO_EXTEND : SIGN_EXTEND), mode, >> >> x); >> >> record_value_for_reg (reg, first, x); >> >> } >> >> >> >> It matches function.c: >> >> >> >> /* This is not really promoting for a call. However we need to be >> >> consistent with assign_parm_find_data_types and expand_expr_real_1. >> >> */ >> >> promoted_nominal_mode >> >> = promote_mode (data->nominal_type, data->nominal_mode, &unsignedp, >> >> 1); >> >> >> >> r128618 changed >> >> >> >> mode = promote_mode (TREE_TYPE (arg), mode, &uns, 1); >> >> >> >> to >> >> >> >> mode3 = promote_mode (DECL_ARG_TYPE (arg), mode2, &uns3, 1); >> >> >> >> It breaks none WORD_REGISTER_OPERATIONS targets. >> > >> > Hmm, I think that DECL_ARG_TYPE makes a difference only >> > for non-WORD_REGISTER_OPERATIONS targets. >> > >> > But yeah, isolated the above change looks wrong. >> > >> > Your patch is ok for trunk if nobody objects within 24h and for branches >> > after a week. >> > >> > Thanks, >> > Richard. >> >> This patch caused PR64213. >> > > Here is the updated patch. The difference is > > mode3 = promote_function_mode (TREE_TYPE (arg), mode1, &uns3, > TREE_TYPE (cfun->decl), 0); > > vs > > mode3 = promote_function_mode (TREE_TYPE (arg), mode1, &uns1, > TREE_TYPE (cfun->decl), 0); > > I made a mistake in my previous patch where I shouldn't have changed > &uns3 to &uns1. We do want to update mode3 and uns3, not mode3 and > uns1. It generates the same code on PR64213 testcase with a cross > alpha-linux GCC. > > Uros, can you test it on Linux/alpha? OK for master, 4.9 and 4.8 > branches if it works on Linux/alpha? Yes, this patch works OK [1] on linux/alpha mainline. [1] https://gcc.gnu.org/ml/gcc-testresults/2014-12/msg01867.html Uros.
