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Tue, 24 May 2016 06:58:36 -0700 (PDT) In-Reply-To: References: Date: Tue, 24 May 2016 19:28:36 +0530 Message-ID: Subject: Re: RFC [1/2] divmod transform From: Prathamesh Kulkarni To: Richard Biener Cc: Richard Biener , gcc Patches , Ramana Radhakrishnan , Kugan Vivekanandarajah , Jim Wilson X-IsSubscribed: yes On 24 May 2016 at 17:42, Richard Biener wrote: > On Tue, 24 May 2016, Prathamesh Kulkarni wrote: > >> On 23 May 2016 at 17:35, Richard Biener wrote: >> > On Mon, May 23, 2016 at 10:58 AM, Prathamesh Kulkarni >> > wrote: >> >> Hi, >> >> I have updated my patch for divmod (attached), which was originally >> >> based on Kugan's patch. >> >> The patch transforms stmts with code TRUNC_DIV_EXPR and TRUNC_MOD_EXPR >> >> having same operands to divmod representation, so we can cse computation of mod. >> >> >> >> t1 = a TRUNC_DIV_EXPR b; >> >> t2 = a TRUNC_MOD_EXPR b >> >> is transformed to: >> >> complex_tmp = DIVMOD (a, b); >> >> t1 = REALPART_EXPR (complex_tmp); >> >> t2 = IMAGPART_EXPR (complex_tmp); >> >> >> >> * New hook divmod_expand_libfunc >> >> The rationale for introducing the hook is that different targets have >> >> incompatible calling conventions for divmod libfunc. >> >> Currently three ports define divmod libfunc: c6x, spu and arm. >> >> c6x and spu follow the convention of libgcc2.c:__udivmoddi4: >> >> return quotient and store remainder in argument passed as pointer, >> >> while the arm version takes two arguments and returns both >> >> quotient and remainder having mode double the size of the operand mode. >> >> The port should hence override the hook expand_divmod_libfunc >> >> to generate call to target-specific divmod. >> >> Ports should define this hook if: >> >> a) The port does not have divmod or div insn for the given mode. >> >> b) The port defines divmod libfunc for the given mode. >> >> The default hook default_expand_divmod_libfunc() generates call >> >> to libgcc2.c:__udivmoddi4 provided the operands are unsigned and >> >> are of DImode. >> >> >> >> Patch passes bootstrap+test on x86_64-unknown-linux-gnu and >> >> cross-tested on arm*-*-*. >> >> Bootstrap+test in progress on arm-linux-gnueabihf. >> >> Does this patch look OK ? >> > >> > diff --git a/gcc/targhooks.c b/gcc/targhooks.c >> > index 6b4601b..e4a021a 100644 >> > --- a/gcc/targhooks.c >> > +++ b/gcc/targhooks.c >> > @@ -1965,4 +1965,31 @@ default_optab_supported_p (int, machine_mode, >> > machine_mode, optimization_type) >> > return true; >> > } >> > >> > +void >> > +default_expand_divmod_libfunc (bool unsignedp, machine_mode mode, >> > + rtx op0, rtx op1, >> > + rtx *quot_p, rtx *rem_p) >> > >> > functions need a comment. >> > >> > ISTR it was suggested that ARM change to libgcc2.c__udivmoddi4 style? In that >> > case we could avoid the target hook. >> Well I would prefer adding the hook because that's more easier -;) >> Would it be ok for now to go with the hook ? >> > >> > + /* If target overrides expand_divmod_libfunc hook >> > + then perform divmod by generating call to the target-specifc divmod >> > libfunc. */ >> > + if (targetm.expand_divmod_libfunc != default_expand_divmod_libfunc) >> > + return true; >> > + >> > + /* Fall back to using libgcc2.c:__udivmoddi4. */ >> > + return (mode == DImode && unsignedp); >> > >> > I don't understand this - we know optab_libfunc returns non-NULL for 'mode' >> > but still restrict this to DImode && unsigned? Also if >> > targetm.expand_divmod_libfunc >> > is not the default we expect the target to handle all modes? >> Ah indeed, the check for DImode is unnecessary. >> However I suppose the check for unsignedp should be there, >> since we want to generate call to __udivmoddi4 only if operand is unsigned ? > > The optab libfunc for sdivmod should be NULL in that case. Ah indeed, thanks. > >> > >> > That said - I expected the above piece to be simply a 'return true;' ;) >> > >> > Usually we use some can_expand_XXX helper in optabs.c to query if the target >> > supports a specific operation (for example SImode divmod would use DImode >> > divmod by means of widening operands - for the unsigned case of course). >> Thanks for pointing out. So if a target does not support divmod >> libfunc for a mode >> but for a wider mode, then we could zero-extend operands to the wider-mode, >> perform divmod on the wider-mode, and then cast result back to the >> original mode. >> I haven't done that in this patch, would it be OK to do that as a follow up ? > > I think that you should conservatively handle the div_optab query, thus if > the target has a HW division in a wider mode don't use the divmod IFN. > You'd simply iterate over GET_MODE_WIDER_MODE and repeat the > if (optab_handler (div_optab, mode) != CODE_FOR_nothing) check, bailing > out if that is available. Done. > >> > + /* Disable the transform if either is a constant, since >> > division-by-constant >> > + may have specialized expansion. */ >> > + if (TREE_CONSTANT (op1) || TREE_CONSTANT (op2)) >> > + return false; >> > >> > please use CONSTANT_CLASS_P (op1) || CONSTANT_CLASS_P (op2) >> > >> > + if (TYPE_OVERFLOW_TRAPS (type)) >> > + return false; >> > >> > why's that? Generally please first test cheap things (trapping, constant-ness) >> > before checking expensive stuff (target_supports_divmod_p). >> I added TYPE_OVERFLOW_TRAPS (type) based on your suggestion in: >> https://www.mail-archive.com/gcc@gcc.gnu.org/msg78534.html >> "When looking at TRUNC_DIV_EXPR you should also exclude >> the case where TYPE_OVERFLOW_TRAPS (type) as that should >> expand using the [su]divv optabs (no trapping overflow >> divmod optab exists)." > > Ok, didn't remember that. > >> > >> > +static bool >> > +convert_to_divmod (gassign *stmt) >> > +{ >> > + if (!divmod_candidate_p (stmt)) >> > + return false; >> > + >> > + tree op1 = gimple_assign_rhs1 (stmt); >> > + tree op2 = gimple_assign_rhs2 (stmt); >> > + >> > + vec stmts = vNULL; >> > >> > use an auto_vec - you currently leak it in at least one place. >> > >> > + if (maybe_clean_or_replace_eh_stmt (use_stmt, use_stmt)) >> > + cfg_changed = true; >> > >> > note that this suggests you should check whether any of the stmts may throw >> > internally as you don't update / transfer EH info correctly. So for 'stmt' and >> > all 'use_stmt' check stmt_can_throw_internal and if so do not add it to >> > the list of stmts to modify. >> > >> > Btw, I think you should not add 'stmt' immediately but when iterating over >> > all uses also gather uses in TRUNC_MOD_EXPR. >> > >> > Otherwise looks ok. >> Done changes in this version. I am gathering mod uses same time as div uses, >> so this imposes a constraint that mod dominates mod. I am not sure if >> that's desirable. > > I think you also need a mod_seen variable now that you don't necessarily > end up with 'stmt' in the vector of stmts. I don't see how there is a > constraint that mod dominates mod - it's just that the top_stmt needs > to dominate all other uses that can be replaced with replacing top_stmt > with a divmod. It's just that the actual stmt set we choose may now > depend on immediate uses order which on a second thought is bad > as immediate uses order could be affected by debug stmts ... hmm. > > To avoid this please re-add the code adding 'stmt' to stmts immediately > and add a use_stmt != stmt check to the immediate use processing loop > so that we don't end up adding it twice. Well I wonder what will happen for the following case: t1 = x / y; if (cond) t2 = x % y; else t3 = x % y; Assuming stmt == top_stmt is "t2 = x % y" and use_stmt is "t3 = x % y", use_stmt will not get added to stmts vector, since top_stmt and use_stmt are not in same bb, and bb's containing top_stmt and use_stmt don't dominate each other. Not sure if this is practical case (I assume fre will hoist mod outside if-else?) Now that we immediately add stmt to stmts vector, I suppose mod_seen shall not be required ? Thanks, Prathamesh > > Richard. diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi index 8c7f2a1..111f19f 100644 --- a/gcc/doc/tm.texi +++ b/gcc/doc/tm.texi @@ -6963,6 +6963,12 @@ This is firstly introduced on ARM/AArch64 targets, please refer to the hook implementation for how different fusion types are supported. @end deftypefn +@deftypefn {Target Hook} void TARGET_EXPAND_DIVMOD_LIBFUNC (bool @var{unsignedp}, machine_mode @var{mode}, @var{rtx}, @var{rtx}, rtx *@var{quot}, rtx *@var{rem}) +Define this hook if the port does not have hardware div and divmod insn for +the given mode but has divmod libfunc, which is incompatible +with libgcc2.c:__udivmoddi4 +@end deftypefn + @node Sections @section Dividing the Output into Sections (Texts, Data, @dots{}) @c the above section title is WAY too long. maybe cut the part between diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in index f963a58..2c9a800 100644 --- a/gcc/doc/tm.texi.in +++ b/gcc/doc/tm.texi.in @@ -4848,6 +4848,8 @@ them: try the first ones in this list first. @hook TARGET_SCHED_FUSION_PRIORITY +@hook TARGET_EXPAND_DIVMOD_LIBFUNC + @node Sections @section Dividing the Output into Sections (Texts, Data, @dots{}) @c the above section title is WAY too long. maybe cut the part between diff --git a/gcc/internal-fn.c b/gcc/internal-fn.c index c867ddc..0cb59f7 100644 --- a/gcc/internal-fn.c +++ b/gcc/internal-fn.c @@ -2276,6 +2276,48 @@ multi_vector_optab_supported_p (convert_optab optab, tree_pair types, #define direct_mask_store_optab_supported_p direct_optab_supported_p #define direct_store_lanes_optab_supported_p multi_vector_optab_supported_p +/* Expand DIVMOD() using: + a) optab handler for udivmod/sdivmod if it is available. + b) If optab_handler doesn't exist, Generate call to + optab_libfunc for udivmod/sdivmod. */ + +static void +expand_DIVMOD (internal_fn, gcall *stmt) +{ + tree lhs = gimple_call_lhs (stmt); + tree arg0 = gimple_call_arg (stmt, 0); + tree arg1 = gimple_call_arg (stmt, 1); + + gcc_assert (TREE_CODE (TREE_TYPE (lhs)) == COMPLEX_TYPE); + tree type = TREE_TYPE (TREE_TYPE (lhs)); + machine_mode mode = TYPE_MODE (type); + bool unsignedp = TYPE_UNSIGNED (type); + optab tab = (unsignedp) ? udivmod_optab : sdivmod_optab; + + rtx op0 = expand_normal (arg0); + rtx op1 = expand_normal (arg1); + rtx target = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE); + + rtx quotient, remainder; + + /* Check if optab handler exists for [u]divmod. */ + if (optab_handler (tab, mode) != CODE_FOR_nothing) + { + quotient = gen_reg_rtx (mode); + remainder = gen_reg_rtx (mode); + expand_twoval_binop (tab, op0, op1, quotient, remainder, unsignedp); + } + else + targetm.expand_divmod_libfunc (unsignedp, mode, op0, op1, + "ient, &remainder); + + /* Wrap the return value (quotient, remainder) within COMPLEX_EXPR. */ + expand_expr (build2 (COMPLEX_EXPR, TREE_TYPE (lhs), + make_tree (TREE_TYPE (arg0), quotient), + make_tree (TREE_TYPE (arg1), remainder)), + target, VOIDmode, EXPAND_NORMAL); +} + /* Return true if FN is supported for the types in TYPES when the optimization type is OPT_TYPE. The types are those associated with the "type0" and "type1" fields of FN's direct_internal_fn_info diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def index e729d85..56a80f1 100644 --- a/gcc/internal-fn.def +++ b/gcc/internal-fn.def @@ -194,6 +194,9 @@ DEF_INTERNAL_FN (ATOMIC_BIT_TEST_AND_SET, ECF_LEAF | ECF_NOTHROW, NULL) DEF_INTERNAL_FN (ATOMIC_BIT_TEST_AND_COMPLEMENT, ECF_LEAF | ECF_NOTHROW, NULL) DEF_INTERNAL_FN (ATOMIC_BIT_TEST_AND_RESET, ECF_LEAF | ECF_NOTHROW, NULL) +/* Divmod function. */ +DEF_INTERNAL_FN (DIVMOD, ECF_CONST | ECF_LEAF, NULL) + #undef DEF_INTERNAL_INT_FN #undef DEF_INTERNAL_FLT_FN #undef DEF_INTERNAL_OPTAB_FN diff --git a/gcc/target.def b/gcc/target.def index 6392e73..4496f9a 100644 --- a/gcc/target.def +++ b/gcc/target.def @@ -4948,6 +4948,16 @@ Normally, this is not needed.", bool, (const_tree field, machine_mode mode), default_member_type_forces_blk) +/* See tree-ssa-math-opts.c:divmod_candidate_p for conditions that gate + the divmod transform. */ +DEFHOOK +(expand_divmod_libfunc, + "Define this hook if the port does not have hardware div and divmod insn for\n\ +the given mode but has divmod libfunc, which is incompatible\n\ +with libgcc2.c:__udivmoddi4", + void, (bool unsignedp, machine_mode mode, rtx, rtx, rtx *quot, rtx *rem), + default_expand_divmod_libfunc) + /* Return the class for a secondary reload, and fill in extra information. */ DEFHOOK (secondary_reload, diff --git a/gcc/targhooks.c b/gcc/targhooks.c index 6b4601b..20327a6 100644 --- a/gcc/targhooks.c +++ b/gcc/targhooks.c @@ -1965,4 +1965,31 @@ default_optab_supported_p (int, machine_mode, machine_mode, optimization_type) return true; } +/* Generate call to + DImode __udivmoddi4 (DImode op0, DImode op1, DImode *rem). */ + +void +default_expand_divmod_libfunc (bool unsignedp, machine_mode mode, + rtx op0, rtx op1, + rtx *quot_p, rtx *rem_p) +{ + gcc_assert (mode == DImode); + gcc_assert (unsignedp); + + rtx libfunc = optab_libfunc (udivmod_optab, DImode); + gcc_assert (libfunc); + + rtx remainder = assign_stack_temp (DImode, GET_MODE_SIZE (DImode)); + rtx address = XEXP (remainder, 0); + + rtx quotient = emit_library_call_value (libfunc, NULL_RTX, LCT_CONST, + DImode, 3, + op0, GET_MODE (op0), + op1, GET_MODE (op1), + address, GET_MODE (address)); + + *quot_p = quotient; + *rem_p = remainder; +} + #include "gt-targhooks.h" diff --git a/gcc/targhooks.h b/gcc/targhooks.h index 7687c39..dc5e8e7 100644 --- a/gcc/targhooks.h +++ b/gcc/targhooks.h @@ -254,4 +254,7 @@ extern void default_setup_incoming_vararg_bounds (cumulative_args_t ca ATTRIBUTE extern bool default_optab_supported_p (int, machine_mode, machine_mode, optimization_type); +extern void default_expand_divmod_libfunc (bool, machine_mode, + rtx, rtx, rtx *, rtx *); + #endif /* GCC_TARGHOOKS_H */ diff --git a/gcc/tree-ssa-math-opts.c b/gcc/tree-ssa-math-opts.c index 81688cd..242b676 100644 --- a/gcc/tree-ssa-math-opts.c +++ b/gcc/tree-ssa-math-opts.c @@ -112,6 +112,9 @@ along with GCC; see the file COPYING3. If not see #include "params.h" #include "internal-fn.h" #include "case-cfn-macros.h" +#include "optabs-libfuncs.h" +#include "tree-eh.h" +#include "targhooks.h" /* This structure represents one basic block that either computes a division, or is a common dominator for basic block that compute a @@ -184,6 +187,9 @@ static struct /* Number of fp fused multiply-add ops inserted. */ int fmas_inserted; + + /* Number of divmod calls inserted. */ + int divmod_calls_inserted; } widen_mul_stats; /* The instance of "struct occurrence" representing the highest @@ -3784,6 +3790,196 @@ match_uaddsub_overflow (gimple_stmt_iterator *gsi, gimple *stmt, return true; } +/* Return true if target has support for divmod. */ + +static bool +target_supports_divmod_p (optab divmod_optab, optab div_optab, machine_mode mode) +{ + /* If target supports hardware divmod insn, use it for divmod. */ + if (optab_handler (divmod_optab, mode) != CODE_FOR_nothing) + return true; + + /* Check if libfunc for divmod is available. */ + if (optab_libfunc (divmod_optab, mode) != NULL_RTX) + { + /* If optab_handler exists for div_optab, perhaps in a wider mode, + we don't want to use the libfunc even if it exists for given mode. */ + for (machine_mode div_mode = mode; + div_mode != VOIDmode; + div_mode = GET_MODE_WIDER_MODE (div_mode)) + if (optab_handler (div_optab, div_mode) != CODE_FOR_nothing) + return false; + + return true; + } + + return false; +} + +/* Check if stmt is candidate for divmod transform. */ + +static bool +divmod_candidate_p (gassign *stmt) +{ + tree type = TREE_TYPE (gimple_assign_lhs (stmt)); + enum machine_mode mode = TYPE_MODE (type); + optab divmod_optab, div_optab; + + if (TYPE_UNSIGNED (type)) + { + divmod_optab = udivmod_optab; + div_optab = udiv_optab; + } + else + { + divmod_optab = sdivmod_optab; + div_optab = sdiv_optab; + } + + tree op1 = gimple_assign_rhs1 (stmt); + tree op2 = gimple_assign_rhs2 (stmt); + + /* Disable the transform if either is a constant, since division-by-constant + may have specialized expansion. */ + if (CONSTANT_CLASS_P (op1) || CONSTANT_CLASS_P (op2)) + return false; + + /* Exclude the case where TYPE_OVERFLOW_TRAPS (type) as that should + expand using the [su]divv optabs. */ + if (TYPE_OVERFLOW_TRAPS (type)) + return false; + + if (!target_supports_divmod_p (divmod_optab, div_optab, mode)) + return false; + + return true; +} + +/* This function looks for: + t1 = a TRUNC_DIV_EXPR b; + t2 = a TRUNC_MOD_EXPR b; + and transforms it to the following sequence: + complex_tmp = DIVMOD (a, b); + t1 = REALPART_EXPR(a); + t2 = IMAGPART_EXPR(b); + For conditions enabling the transform see divmod_candidate_p(). + + The pass works in two phases: + 1) Walk through all immediate uses of stmt's operand and find a + TRUNC_DIV_EXPR with matching operands and if such a stmt is found add + it to stmts vector. + 2) Insert DIVMOD call before first div/mod stmt in top_bb (basic block that + dominates other div/mod stmts with same operands) and update entries in + stmts vector to use return value of DIMOVD (REALEXPR_PART for div, + IMAGPART_EXPR for mod). */ + +static bool +convert_to_divmod (gassign *stmt) +{ + if (!divmod_candidate_p (stmt)) + return false; + + tree op1 = gimple_assign_rhs1 (stmt); + tree op2 = gimple_assign_rhs2 (stmt); + gimple *top_stmt = stmt; + basic_block top_bb = gimple_bb (top_stmt); + bool div_seen = false; + imm_use_iterator use_iter; + gimple *use_stmt; + auto_vec stmts; + + stmts.safe_push (stmt); + FOR_EACH_IMM_USE_STMT (use_stmt, use_iter, op1) + { + /* Check if use_stmt is TRUNC_DIV_EXPR with same operands as stmt. */ + if (is_gimple_assign (use_stmt) + && (gimple_assign_rhs_code (use_stmt) == TRUNC_DIV_EXPR + || gimple_assign_rhs_code (use_stmt) == TRUNC_MOD_EXPR) + && operand_equal_p (op1, gimple_assign_rhs1 (use_stmt), 0) + && operand_equal_p (op2, gimple_assign_rhs2 (use_stmt), 0)) + { + if (stmt_can_throw_internal (use_stmt)) + continue; + + if (use_stmt == stmt) + continue; + + basic_block bb = gimple_bb (use_stmt); + top_bb = gimple_bb (top_stmt); + + if (top_bb == bb) + { + stmts.safe_push (use_stmt); + if (gimple_uid (use_stmt) < gimple_uid (top_stmt)) + top_stmt = use_stmt; + } + else if (dominated_by_p (CDI_DOMINATORS, top_bb, bb)) + { + stmts.safe_push (use_stmt); + top_stmt = use_stmt; + } + else if (dominated_by_p (CDI_DOMINATORS, bb, top_bb)) + stmts.safe_push (use_stmt); + else + continue; + + if (gimple_assign_rhs_code (use_stmt) == TRUNC_DIV_EXPR) + div_seen = true; + } + } + + if (!div_seen) + return false; + + /* Create libcall to internal fn DIVMOD: + divmod_tmp = DIVMOD (op1, op2). */ + + gcall *call_stmt = gimple_build_call_internal (IFN_DIVMOD, 2, op1, op2); + tree res = make_temp_ssa_name ( + build_complex_type (TREE_TYPE (op1)), + call_stmt, "divmod_tmp"); + gimple_call_set_lhs (call_stmt, res); + + /* Insert the call before top_stmt. */ + gimple_stmt_iterator top_stmt_gsi = gsi_for_stmt (top_stmt); + gsi_insert_before (&top_stmt_gsi, call_stmt, GSI_SAME_STMT); + + widen_mul_stats.divmod_calls_inserted++; + + /* Update all statements in stmts. + if stmt is lhs = op1 TRUNC_DIV_EXPR op2, change to lhs = REALPART_EXPR + if stmt is lhs = op1 TRUNC_MOD_EXPR op2, change to lhs = IMAGPART_EXPR. */ + + bool cfg_changed = false; + for (unsigned i = 0; stmts.iterate (i, &use_stmt); ++i) + { + tree new_rhs; + + switch (gimple_assign_rhs_code (use_stmt)) + { + case TRUNC_DIV_EXPR: + new_rhs = fold_build1 (REALPART_EXPR, TREE_TYPE (op1), res); + break; + + case TRUNC_MOD_EXPR: + new_rhs = fold_build1 (IMAGPART_EXPR, TREE_TYPE (op2), res); + break; + + default: + gcc_unreachable (); + } + + gimple_stmt_iterator gsi = gsi_for_stmt (use_stmt); + gimple_assign_set_rhs_from_tree (&gsi, new_rhs); + update_stmt (use_stmt); + + if (maybe_clean_or_replace_eh_stmt (use_stmt, use_stmt)) + cfg_changed = true; + } + + stmts.release (); + return cfg_changed; +} /* Find integer multiplications where the operands are extended from smaller types, and replace the MULT_EXPR with a WIDEN_MULT_EXPR @@ -3828,6 +4024,8 @@ pass_optimize_widening_mul::execute (function *fun) bool cfg_changed = false; memset (&widen_mul_stats, 0, sizeof (widen_mul_stats)); + calculate_dominance_info (CDI_DOMINATORS); + renumber_gimple_stmt_uids (); FOR_EACH_BB_FN (bb, fun) { @@ -3861,6 +4059,10 @@ pass_optimize_widening_mul::execute (function *fun) match_uaddsub_overflow (&gsi, stmt, code); break; + case TRUNC_MOD_EXPR: + cfg_changed = convert_to_divmod (as_a (stmt)); + break; + default:; } } @@ -3907,6 +4109,8 @@ pass_optimize_widening_mul::execute (function *fun) widen_mul_stats.maccs_inserted); statistics_counter_event (fun, "fused multiply-adds inserted", widen_mul_stats.fmas_inserted); + statistics_counter_event (fun, "divmod calls inserted", + widen_mul_stats.divmod_calls_inserted); return cfg_changed ? TODO_cleanup_cfg : 0; }