From patchwork Thu May 3 14:33:56 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Bill Schmidt X-Patchwork-Id: 156707 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from sourceware.org (server1.sourceware.org [209.132.180.131]) by ozlabs.org (Postfix) with SMTP id 05393B6FA5 for ; Fri, 4 May 2012 00:36:51 +1000 (EST) Comment: DKIM? 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Violators will be prosecuted; Thu, 3 May 2012 08:35:00 -0600 Received: from d01relay06.pok.ibm.com (d01relay06.pok.ibm.com [9.56.227.116]) by d01dlp03.pok.ibm.com (Postfix) with ESMTP id 281A5C90081 for ; Thu, 3 May 2012 10:34:57 -0400 (EDT) Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by d01relay06.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q43EYoRd16318626 for ; Thu, 3 May 2012 10:34:51 -0400 Received: from d03av06.boulder.ibm.com (loopback [127.0.0.1]) by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q43EYaq4010633 for ; Thu, 3 May 2012 08:34:36 -0600 Received: from [9.80.52.106] ([9.80.52.106]) by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id q43EYX24010489; Thu, 3 May 2012 08:34:34 -0600 Message-ID: <1336055636.22269.16.camel@gnopaine> Subject: [PATCH] Hoist adjacent pointer loads From: "William J. Schmidt" To: gcc-patches@gcc.gnu.org Cc: rguenther@suse.de, bergner@vnet.ibm.com Date: Thu, 03 May 2012 09:33:56 -0500 Mime-Version: 1.0 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12050314-2398-0000-0000-00000652725D Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org Delivered-To: mailing list gcc-patches@gcc.gnu.org This patch was posted for comment back in February during stage 4. It addresses a performance issue noted in the EEMBC routelookup benchmark on a common idiom: if (...) x = y->left; else x = y->right; If the two loads can be hoisted out of the if/else, the if/else can be replaced by a conditional move instruction on architectures that support one. Because this speculates one of the loads, the patch constrains the optimization to avoid introducing page faults. Bootstrapped and regression tested on powerpc-unknown-linux-gnu with no new failures. The patch provides significant improvement to the routelookup benchmark, and is neutral on SPEC cpu2000/cpu2006. One question is what optimization level should be required for this. Because of the speculation, -O3 might be in order. I don't believe -Ofast is required as there is no potential correctness issue involved. Right now the patch doesn't check the optimization level (like the rest of the phi-opt transforms), which is likely a poor choice. Ok for trunk? Thanks, Bill 2012-05-03 Bill Schmidt * tree-ssa-phiopt.c (tree_ssa_phiopt_worker): Add argument to forward declaration. (hoist_adjacent_loads, gate_hoist_loads): New forward declarations. (tree_ssa_phiopt): Call gate_hoist_loads. (tree_ssa_cs_elim): Add parm to tree_ssa_phiopt_worker call. (tree_ssa_phiopt_worker): Add do_hoist_loads to formal arg list; call hoist_adjacent_loads. (local_reg_dependence): New function. (local_mem_dependence): Likewise. (hoist_adjacent_loads): Likewise. (gate_hoist_loads): Likewise. * common.opt (fhoist-adjacent-loads): New switch. * Makefile.in (tree-ssa-phiopt.o): Added dependencies. * params.def (PARAM_MIN_CMOVE_STRUCT_ALIGN): New param. Index: gcc/tree-ssa-phiopt.c =================================================================== --- gcc/tree-ssa-phiopt.c (revision 187057) +++ gcc/tree-ssa-phiopt.c (working copy) @@ -37,9 +37,17 @@ along with GCC; see the file COPYING3. If not see #include "cfgloop.h" #include "tree-data-ref.h" #include "tree-pretty-print.h" +#include "gimple-pretty-print.h" +#include "insn-config.h" +#include "expr.h" +#include "optabs.h" +#ifndef HAVE_conditional_move +#define HAVE_conditional_move (0) +#endif + static unsigned int tree_ssa_phiopt (void); -static unsigned int tree_ssa_phiopt_worker (bool); +static unsigned int tree_ssa_phiopt_worker (bool, bool); static bool conditional_replacement (basic_block, basic_block, edge, edge, gimple, tree, tree); static int value_replacement (basic_block, basic_block, @@ -53,6 +61,9 @@ static bool cond_store_replacement (basic_block, b static bool cond_if_else_store_replacement (basic_block, basic_block, basic_block); static struct pointer_set_t * get_non_trapping (void); static void replace_phi_edge_with_variable (basic_block, edge, gimple, tree); +static void hoist_adjacent_loads (basic_block, basic_block, + basic_block, basic_block); +static bool gate_hoist_loads (void); /* This pass tries to replaces an if-then-else block with an assignment. We have four kinds of transformations. Some of these @@ -138,12 +149,56 @@ static void replace_phi_edge_with_variable (basic_ bb2: x = PHI ; - A similar transformation is done for MAX_EXPR. */ + A similar transformation is done for MAX_EXPR. + + This pass also performs a fifth transformation of a slightly different + flavor. + + Adjacent Load Hoisting + ---------------------- + + This transformation replaces + + bb0: + if (...) goto bb2; else goto bb1; + bb1: + x1 = ().field1; + goto bb3; + bb2: + x2 = ().field2; + bb3: + # x = PHI ; + + with + + bb0: + x1 = ().field1; + x2 = ().field2; + if (...) goto bb2; else goto bb1; + bb1: + goto bb3; + bb2: + bb3: + # x = PHI ; + + The purpose of this transformation is to enable generation of conditional + move instructions such as Intel CMOVE or PowerPC ISEL. Because one of + the loads is speculative, the transformation is restricted to very + specific cases to avoid introducing a page fault. We are looking for + the common idiom: + + if (...) + x = y->left; + else + x = y->right; + + where left and right are typically adjacent pointers in a tree structure. */ + static unsigned int tree_ssa_phiopt (void) { - return tree_ssa_phiopt_worker (false); + return tree_ssa_phiopt_worker (false, gate_hoist_loads ()); } /* This pass tries to transform conditional stores into unconditional @@ -190,7 +245,7 @@ tree_ssa_phiopt (void) static unsigned int tree_ssa_cs_elim (void) { - return tree_ssa_phiopt_worker (true); + return tree_ssa_phiopt_worker (true, false); } /* Return the singleton PHI in the SEQ of PHIs for edges E0 and E1. */ @@ -227,9 +282,11 @@ static tree condstoretemp; /* The core routine of conditional store replacement and normal phi optimizations. Both share much of the infrastructure in how to match applicable basic block patterns. DO_STORE_ELIM is true - when we want to do conditional store replacement, false otherwise. */ + when we want to do conditional store replacement, false otherwise. + DO_HOIST_LOADS is true when we want to hoist adjacent loads out + of diamond control flow patterns, false otherwise. */ static unsigned int -tree_ssa_phiopt_worker (bool do_store_elim) +tree_ssa_phiopt_worker (bool do_store_elim, bool do_hoist_loads) { basic_block bb; basic_block *bb_order; @@ -312,6 +369,20 @@ static unsigned int cfgchanged = true; continue; } + else if (do_hoist_loads + && EDGE_SUCC (bb1, 0)->dest == EDGE_SUCC (bb2, 0)->dest) + { + basic_block bb3 = EDGE_SUCC (bb1, 0)->dest; + + if (single_succ_p (bb1) + && single_succ_p (bb2) + && single_pred_p (bb1) + && single_pred_p (bb2) + && EDGE_COUNT (bb->succs) == 2 + && EDGE_COUNT (bb3->preds) == 2) + hoist_adjacent_loads (bb, bb1, bb2, bb3); + continue; + } else continue; @@ -1707,6 +1778,220 @@ cond_if_else_store_replacement (basic_block then_b return ok; } +/* Return TRUE iff EXPR contains any SSA names that are defined in BB. */ + +static bool +local_reg_dependence (tree expr, basic_block bb) +{ + int i; + + if (TREE_CODE (expr) == SSA_NAME) + { + if (SSA_NAME_IS_DEFAULT_DEF (expr)) + return false; + else + return (gimple_bb (SSA_NAME_DEF_STMT (expr)) == bb); + } + + for (i = 0; i < TREE_OPERAND_LENGTH (expr); i++) + if (TREE_OPERAND (expr, i) + && local_reg_dependence (TREE_OPERAND (expr, i), bb)) + return true; + + return false; +} + +/* Return TRUE if STMT has a VUSE whose corresponding VDEF is in BB. */ + +static bool +local_mem_dependence (gimple stmt, basic_block bb) +{ + tree vuse = gimple_vuse (stmt); + gimple def; + + if (!vuse) + return false; + + def = SSA_NAME_DEF_STMT (vuse); + return (def && gimple_bb (def) == bb); +} + +/* Given a "diamond" control-flow pattern where BB0 tests a condition, + BB1 and BB2 are "then" and "else" blocks dependent on this test, + and BB3 rejoins control flow following BB1 and BB2, look for + opportunities to hoist loads as follows. If BB3 contains a PHI of + two loads, one each occurring in BB1 and BB2, and the loads are + provably of adjacent fields in the same structure, then move both + loads into BB0. Of course this can only be done if there are no + dependencies preventing such motion. + + One of the hoisted loads will always be speculative, so the + transformation is currently conservative: + + - The fields must be strictly adjacent. + - Hoisting is only done on aligned pointer fields. + - The two fields must occupy a single memory block that is + guaranteed to not cross a page boundary. + + The last is difficult to prove, as such memory blocks should be + aligned on the minimum of the stack alignment boundary and the + alignment guaranteed by heap allocation interfaces. Thus we rely + on a parameter for the alignment value. + + Provided a good value is used for the last case, the first two + restrictions can probably be relaxed. */ + +static void +hoist_adjacent_loads (basic_block bb0, basic_block bb1, + basic_block bb2, basic_block bb3) +{ + int param_align = PARAM_VALUE (PARAM_MIN_CMOVE_STRUCT_ALIGN); + gimple_stmt_iterator gsi; + + /* Walk the phis in bb3 looking for an opportunity. We are looking + for phis of two SSA names, one each of which is defined in bb1 and + bb2. */ + for (gsi = gsi_start_phis (bb3); !gsi_end_p (gsi); gsi_next (&gsi)) + { + gimple phi_stmt = gsi_stmt (gsi); + gimple def1, def2; + tree arg1, arg2, ref1, ref2, field1, field2; + tree tree_offset1, tree_offset2, tree_size1, tree_size2; + int offset1, offset2, size1, size2, block_offset; + unsigned align1, align2; + gimple_stmt_iterator gsi2; + + if (gimple_phi_num_args (phi_stmt) != 2) + continue; + + arg1 = gimple_phi_arg_def (phi_stmt, 0); + arg2 = gimple_phi_arg_def (phi_stmt, 1); + + if (TREE_CODE (arg1) != SSA_NAME + || TREE_CODE (arg2) != SSA_NAME + || SSA_NAME_IS_DEFAULT_DEF (arg1) + || SSA_NAME_IS_DEFAULT_DEF (arg2) + /* FORNOW: Only do this optimization for pointer types. */ + || !POINTER_TYPE_P (TREE_TYPE (arg1))) + continue; + + def1 = SSA_NAME_DEF_STMT (arg1); + def2 = SSA_NAME_DEF_STMT (arg2); + + if ((gimple_bb (def1) != bb1 || gimple_bb (def2) != bb2) + && (gimple_bb (def2) != bb1 || gimple_bb (def1) != bb2)) + continue; + + /* Unless -fhoist-adjacent-loads was specified, check the mode + of the arguments to be sure a conditional move can be generated + for it. */ + if (flag_hoist_adjacent_loads != 1 + && !optab_handler (cmov_optab, TYPE_MODE (TREE_TYPE (arg1)))) + continue; + + /* Both statements must be assignments whose RHS is a COMPONENT_REF. */ + if (!gimple_assign_single_p (def1) + || !gimple_assign_single_p (def2)) + continue; + + ref1 = gimple_assign_rhs1 (def1); + ref2 = gimple_assign_rhs1 (def2); + + if (TREE_CODE (ref1) != COMPONENT_REF + || TREE_CODE (ref2) != COMPONENT_REF) + continue; + + /* The zeroth operand of the two component references must be + identical. It is not sufficient to compare get_base_address of + the two references, because this could allow for different + elements of the same array in the two trees. It is not safe to + assume that the existence of one array element implies the + existence of a different one. */ + if (!operand_equal_p (TREE_OPERAND (ref1, 0), TREE_OPERAND (ref2, 0), 0)) + continue; + + field1 = TREE_OPERAND (ref1, 1); + field2 = TREE_OPERAND (ref2, 1); + + tree_offset1 = DECL_FIELD_BIT_OFFSET (field1); + tree_offset2 = DECL_FIELD_BIT_OFFSET (field2); + tree_size1 = DECL_SIZE_UNIT (field1); + tree_size2 = DECL_SIZE_UNIT (field2); + + if (TREE_CODE (tree_offset1) != INTEGER_CST + || TREE_CODE (tree_offset2) != INTEGER_CST + || TREE_CODE (tree_size1) != INTEGER_CST + || TREE_CODE (tree_size2) != INTEGER_CST) + continue; + + /* FORNOW: The two field references must be byte-aligned, naturally + aligned within the record, and adjacent. */ + offset1 = TREE_INT_CST_LOW (tree_offset1); + offset2 = TREE_INT_CST_LOW (tree_offset2); + size1 = TREE_INT_CST_LOW (tree_size1); + size2 = TREE_INT_CST_LOW (tree_size2); + align1 = TYPE_ALIGN (TREE_TYPE (arg1)); + align2 = TYPE_ALIGN (TREE_TYPE (arg2)); + + if (offset1 % BITS_PER_UNIT != 0 + || offset2 % BITS_PER_UNIT != 0 + || offset1 % align1 != 0 + || offset2 % align2 != 0) + continue; + + offset1 /= BITS_PER_UNIT; + offset2 /= BITS_PER_UNIT; + + if (offset1 + size1 != offset2 + && offset2 + size2 != offset1) + continue; + + /* The two field references must fit within a block of memory that + is guaranteed to be on the same page. */ + block_offset = MIN (offset1, offset2) % param_align; + + if (block_offset + size1 + size2 > param_align) + continue; + + /* The two expressions cannot be dependent upon SSA names + or vdefs defined in bb1/bb2. */ + if (local_reg_dependence (TREE_OPERAND (ref1, 0), bb1) + || local_reg_dependence (TREE_OPERAND (ref2, 0), bb2) + || local_mem_dependence (def1, bb1) + || local_mem_dependence (def2, bb2)) + continue; + + /* The conditions are satisfied; hoist the loads from bb1 and bb2 into + bb0. */ + gsi2 = gsi_for_stmt (def1); + gsi_move_to_bb_end (&gsi2, bb0); + gsi2 = gsi_for_stmt (def2); + gsi_move_to_bb_end (&gsi2, bb0); + + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, + "\nHoisting adjacent loads from %d and %d into %d: \n", + bb1->index, bb2->index, bb0->index); + print_gimple_stmt (dump_file, def1, 0, TDF_VOPS|TDF_MEMSYMS); + print_gimple_stmt (dump_file, def2, 0, TDF_VOPS|TDF_MEMSYMS); + } + } +} + +/* Determine whether we should attempt to hoist adjacent loads out of + diamond patterns in pass_phiopt. Always hoist loads if + -fhoist-adjacent-loads is specified, or if the target machine has + a conditional move instruction and -fno-hoist-adjacent-loads is + not specified. */ + +static bool +gate_hoist_loads (void) +{ + return (flag_hoist_adjacent_loads == 1 + || (HAVE_conditional_move && flag_hoist_adjacent_loads != 0)); +} + /* Always do these optimizations if we have SSA trees to work on. */ static bool Index: gcc/common.opt =================================================================== --- gcc/common.opt (revision 187057) +++ gcc/common.opt (working copy) @@ -1186,6 +1186,11 @@ fgraphite-identity Common Report Var(flag_graphite_identity) Optimization Enable Graphite Identity transformation +fhoist-adjacent-loads +Common Report Var(flag_hoist_adjacent_loads) Init(-1) Optimization +Enable hoisting adjacent loads to encourage generating conditional move +instructions + floop-parallelize-all Common Report Var(flag_loop_parallelize_all) Optimization Mark all loops as parallel Index: gcc/Makefile.in =================================================================== --- gcc/Makefile.in (revision 187057) +++ gcc/Makefile.in (working copy) @@ -2351,7 +2351,8 @@ tree-ssa-phiopt.o : tree-ssa-phiopt.c $(CONFIG_H) $(TM_H) $(GGC_H) $(TREE_H) $(TM_P_H) $(BASIC_BLOCK_H) \ $(TREE_FLOW_H) $(TREE_PASS_H) $(TREE_DUMP_H) langhooks.h $(FLAGS_H) \ $(DIAGNOSTIC_H) $(TIMEVAR_H) pointer-set.h domwalk.h $(CFGLOOP_H) \ - $(TREE_DATA_REF_H) tree-pretty-print.h + $(TREE_DATA_REF_H) tree-pretty-print.h gimple-pretty-print.h \ + insn-config.h $(EXPR_H) $(OPTABS_H) tree-nrv.o : tree-nrv.c $(CONFIG_H) $(SYSTEM_H) coretypes.h \ $(TM_H) $(TREE_H) $(FUNCTION_H) $(BASIC_BLOCK_H) $(FLAGS_H) \ $(DIAGNOSTIC_H) $(TREE_FLOW_H) $(TIMEVAR_H) $(TREE_DUMP_H) $(TREE_PASS_H) \ Index: gcc/params.def =================================================================== --- gcc/params.def (revision 187057) +++ gcc/params.def (working copy) @@ -979,6 +979,13 @@ DEFPARAM (PARAM_MAX_TRACKED_STRLENS, "track string lengths", 1000, 0, 0) +/* For adjacent load hoisting transformation in tree-ssa-phiopt.c. */ +DEFPARAM (PARAM_MIN_CMOVE_STRUCT_ALIGN, + "min-cmove-struct-align", + "Minimum byte alignment to assume for structures in the stack " + "or heap when considering load hoisting for conditional moves", + 16, 8, 256) + /* Local variables: mode:c