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[58.6.183.210]) by mx.google.com with ESMTPSA id fk10sm11890447pab.29.2014.09.09.03.06.31 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 09 Sep 2014 03:06:33 -0700 (PDT) Message-ID: <540ED116.9030907@linaro.org> Date: Tue, 09 Sep 2014 20:06:14 +1000 From: Kugan User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0 MIME-Version: 1.0 To: Richard Biener CC: Uros Bizjak , "gcc-patches@gcc.gnu.org" , Jakub Jelinek Subject: Re: [PATCH 2/2] Enable elimination of zext/sext References: <53FEDF34.4090605@linaro.org> <5407DF57.2040902@linaro.org> <540912E1.30505@linaro.org> <540C2A7E.7050105@linaro.org> In-Reply-To: X-IsSubscribed: yes On 08/09/14 19:48, Richard Biener wrote: > On Sun, Sep 7, 2014 at 11:50 AM, Kugan > wrote: >> On 05/09/14 19:50, Richard Biener wrote: >> >>> Well - the best way would be to expose the target specifics to GIMPLE >>> at some point in the optimization pipeline. My guess would be that it's >>> appropriate after loop optimizations (but maybe before induction variable >>> optimization). >>> >>> That is, have a pass that applies register promotion to all SSA names >>> in the function, inserting appropriate truncations and extensions. That >>> way you'd never see (set (subreg...) on RTL. The VRP and DOM >>> passes running after that pass would then be able to aggressively >>> optimize redundant truncations and extensions. >>> >>> Effects on debug information are to be considered. You can change >>> the type of SSA names in-place but you don't want to do that for >>> user DECLs (and we can't have the SSA name type and its DECL >>> type differ - and not sure if we might want to lift that restriction). >> >> Thanks. I will try to implement this. >> >> I still would like to keep the VRP based approach as there are some >> cases that I think can only be done with range info. For example: >> >> short foo(unsigned char c) >> { >> c = c & (unsigned char)0x0F; >> if( c > 7 ) >> return((short)(c - 5)); >> else >> return(( short )c); >> } >> >> >> So, how about adding and setting the overflow/wrap around flag to >> range_info. We now set static_flag for VR_RANG/VR_ANTI_RANGE. If we go >> back to the max + 1, min - 1 for VR_ANTI_RANGE, we can use this >> static_flag to encode overflow/wrap around. Will that be something >> acceptable? > > You mean tracking in the VRP lattice whether a value wrapped around > (or was assumed not to due to undefined behavior)? I'm not sure this > is easy to do correctly (VRP is large). > > Note that I don't think we'll lose the testcase you quoted if the promotion > pass runs before VRP2. We'd have as input to VRP2 sth like (assuming > promote mode would promote to SImode) > > SImode tem_2 = (unsigned int)c_1(D); > tem_3 = tem_3 & 0xF; > if (tem_3 > 7) > { > tem_4 = tem_3 - 5; > short _5 = (short)_4; > tem_5 = (unsigned int)_5; > return tem_5; > } > else > { > short _6 = (short)_3; > return _6; > } > > VRP should be able to remove the (unsigned int)(short) sign-extension > of tem_4. > > note that both incoming registers and return registers are "interesting". > For simplicity I suggest to not promote them on GIMPLE. > > What you'd lose in VRP2 is the smaller value-ranges you'd get from > (undefined) wrapping. You could recover the undefinedness by > looking at SSA names recorded value-range and transfering that > in the promotion pass (but I'm not sure if you want to open the > can of latent signed overflow bugs in programs even more for > PROMOTE_MODE targets...) > Thanks. In the meantime I would like to revert the patch which is enabling zero/sign extension. I have bootstrapped it in x86_64 and regression testing is ongoing. Is this OK ? Thanks, Kugan gcc/ChangeLog: 2014-09-09 Kugan Vivekanandarajah Revert r213751: * calls.c (precompute_arguments): Check promoted_for_signed_and_unsigned_p and set the promoted mode. (promoted_for_signed_and_unsigned_p): New function. (expand_expr_real_1): Check promoted_for_signed_and_unsigned_p and set the promoted mode. * expr.h (promoted_for_signed_and_unsigned_p): New function definition. * cfgexpand.c (expand_gimple_stmt_1): Call emit_move_insn if SUBREG is promoted with SRP_SIGNED_AND_UNSIGNED. diff --git a/gcc/calls.c b/gcc/calls.c index 03ed9c8..345331f 100644 --- a/gcc/calls.c +++ b/gcc/calls.c @@ -1486,10 +1486,7 @@ precompute_arguments (int num_actuals, struct arg_data *args) args[i].initial_value = gen_lowpart_SUBREG (mode, args[i].value); SUBREG_PROMOTED_VAR_P (args[i].initial_value) = 1; - if (promoted_for_signed_and_unsigned_p (args[i].tree_value, mode)) - SUBREG_PROMOTED_SET (args[i].initial_value, SRP_SIGNED_AND_UNSIGNED); - else - SUBREG_PROMOTED_SET (args[i].initial_value, args[i].unsignedp); + SUBREG_PROMOTED_SET (args[i].initial_value, args[i].unsignedp); } } } diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c index db76897..8916305 100644 --- a/gcc/cfgexpand.c +++ b/gcc/cfgexpand.c @@ -3325,13 +3325,7 @@ expand_gimple_stmt_1 (gimple stmt) GET_MODE (target), temp, unsignedp); } - if ((SUBREG_PROMOTED_GET (target) == SRP_SIGNED_AND_UNSIGNED) - && (GET_CODE (temp) == SUBREG) - && (GET_MODE (target) == GET_MODE (temp)) - && (GET_MODE (SUBREG_REG (target)) == GET_MODE (SUBREG_REG (temp)))) - emit_move_insn (SUBREG_REG (target), SUBREG_REG (temp)); - else - convert_move (SUBREG_REG (target), temp, unsignedp); + convert_move (SUBREG_REG (target), temp, unsignedp); } else if (nontemporal && emit_storent_insn (target, temp)) ; diff --git a/gcc/expr.c b/gcc/expr.c index 7e69955..5039734 100644 --- a/gcc/expr.c +++ b/gcc/expr.c @@ -68,7 +68,6 @@ along with GCC; see the file COPYING3. If not see #include "tree-ssa-address.h" #include "cfgexpand.h" #include "builtins.h" -#include "tree-ssa.h" #ifndef STACK_PUSH_CODE #ifdef STACK_GROWS_DOWNWARD @@ -9250,35 +9249,6 @@ expand_expr_real_2 (sepops ops, rtx target, enum machine_mode tmode, } #undef REDUCE_BIT_FIELD -/* Return TRUE if value in SSA is zero and sign extended for wider mode MODE - using value range information stored. Return FALSE otherwise. - - This is used to check if SUBREG is zero and sign extended and to set - promoted mode SRP_SIGNED_AND_UNSIGNED to SUBREG. */ - -bool -promoted_for_signed_and_unsigned_p (tree ssa, enum machine_mode mode) -{ - wide_int min, max; - - if (ssa == NULL_TREE - || TREE_CODE (ssa) != SSA_NAME - || !INTEGRAL_TYPE_P (TREE_TYPE (ssa)) - || (TYPE_PRECISION (TREE_TYPE (ssa)) != GET_MODE_PRECISION (mode))) - return false; - - /* Return FALSE if value_range is not recorded for SSA. */ - if (get_range_info (ssa, &min, &max) != VR_RANGE) - return false; - - /* Return true (to set SRP_SIGNED_AND_UNSIGNED to SUBREG) if MSB of the - smaller mode is not set (i.e. MSB of ssa is not set). */ - if (!wi::neg_p (min, SIGNED) && !wi::neg_p(max, SIGNED)) - return true; - else - return false; - -} /* Return TRUE if expression STMT is suitable for replacement. Never consider memory loads as replaceable, because those don't ever lead @@ -9582,10 +9552,7 @@ expand_expr_real_1 (tree exp, rtx target, enum machine_mode tmode, temp = gen_lowpart_SUBREG (mode, decl_rtl); SUBREG_PROMOTED_VAR_P (temp) = 1; - if (promoted_for_signed_and_unsigned_p (ssa_name, mode)) - SUBREG_PROMOTED_SET (temp, SRP_SIGNED_AND_UNSIGNED); - else - SUBREG_PROMOTED_SET (temp, unsignedp); + SUBREG_PROMOTED_SET (temp, unsignedp); return temp; } diff --git a/gcc/expr.h b/gcc/expr.h index 756c894..2e66329 100644 --- a/gcc/expr.h +++ b/gcc/expr.h @@ -440,7 +440,6 @@ extern rtx expand_expr_real_1 (tree, rtx, enum machine_mode, enum expand_modifier, rtx *, bool); extern rtx expand_expr_real_2 (sepops, rtx, enum machine_mode, enum expand_modifier); -extern bool promoted_for_signed_and_unsigned_p (tree, enum machine_mode); /* Generate code for computing expression EXP. An rtx for the computed value is returned. The value is never null.