Hi Richard,
Here's a revision of the hoist-adjacent-loads patch. I'm sorry for the
delay since the last revision, but my performance testing has been
blocked waiting for a fix to PR53487. I ended up applying a test
version of the patch to 4.7 and ran performance numbers with that
instead, with no degradations.
In addition to addressing your comments, this patch contains one bug fix
where local_mem_dependence was called on the wrong blocks after swapping
def1 and def2.
Bootstrapped with no regressions on powerpc64-unknown-linux-gnu. Is
this version ok for trunk? I won't commit it until I can do final
testing on trunk in conjunction with a fix for PR53487.
Thanks,
Bill
2012-06-04 Bill Schmidt <wschm...@linux.vnet.ibm.com>
* opts.c: Add -fhoist_adjacent_loads to -O2 and above.
* 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_mem_dependence): New function.
(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/opts.c
===================================================================
--- gcc/opts.c (revision 187805)
+++ gcc/opts.c (working copy)
@@ -489,6 +489,7 @@ static const struct default_options default_option
{ OPT_LEVELS_2_PLUS, OPT_falign_functions, NULL, 1 },
{ OPT_LEVELS_2_PLUS, OPT_ftree_tail_merge, NULL, 1 },
{ OPT_LEVELS_2_PLUS_SPEED_ONLY, OPT_foptimize_strlen, NULL, 1 },
+ { OPT_LEVELS_2_PLUS, OPT_fhoist_adjacent_loads, NULL, 1 },
/* -O3 optimizations. */
{ OPT_LEVELS_3_PLUS, OPT_ftree_loop_distribute_patterns, NULL, 1 },
Index: gcc/tree-ssa-phiopt.c
===================================================================
--- gcc/tree-ssa-phiopt.c (revision 187805)
+++ 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 <x' (bb0), ...>;
- 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 = (<expr>).field1;
+ goto bb3;
+ bb2:
+ x2 = (<expr>).field2;
+ bb3:
+ # x = PHI <x1, x2>;
+
+ with
+
+ bb0:
+ x1 = (<expr>).field1;
+ x2 = (<expr>).field2;
+ if (...) goto bb2; else goto bb1;
+ bb1:
+ goto bb3;
+ bb2:
+ bb3:
+ # x = PHI <x1, x2>;
+
+ 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 +369,21 @@ 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 (!FLOAT_TYPE_P (TREE_TYPE (gimple_cond_lhs (cond_stmt)))
+ && 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 +1779,207 @@ cond_if_else_store_replacement (basic_block then_b
return ok;
}
+/* 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.
+ - 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
+ restriction could possibly 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);
+ unsigned param_align_bits = (unsigned) (param_align * BITS_PER_UNIT);
+ 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, defswap;
+ tree arg1, arg2, ref1, ref2, field1, field2, fieldswap;
+ tree tree_offset1, tree_offset2, tree_size2, next;
+ int offset1, offset2, size2;
+ unsigned align1;
+ gimple_stmt_iterator gsi2;
+ basic_block bb_for_def1, bb_for_def2;
+
+ 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))
+ 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;
+
+ /* Check the mode of the arguments to be sure a conditional move
+ can be generated for it. */
+ if (!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);
+
+ /* Check for field adjacency, and ensure field1 comes first. */
+ for (next = DECL_CHAIN (field1);
+ next && TREE_CODE (next) != FIELD_DECL;
+ next = DECL_CHAIN (next))
+ ;
+
+ if (next != field2)
+ {
+ for (next = DECL_CHAIN (field2);
+ next && TREE_CODE (next) != FIELD_DECL;
+ next = DECL_CHAIN (next))
+ ;
+
+ if (next != field1)
+ continue;
+
+ fieldswap = field1;
+ field1 = field2;
+ field2 = fieldswap;
+ defswap = def1;
+ def1 = def2;
+ def2 = defswap;
+ /* Don't swap bb1 and bb2 as we may have more than one
+ phi to process successfully. */
+ bb_for_def1 = bb2;
+ bb_for_def2 = bb1;
+ }
+ else
+ {
+ bb_for_def1 = bb1;
+ bb_for_def2 = bb2;
+ }
+
+ /* Check for proper alignment of the first field. */
+ tree_offset1 = bit_position (field1);
+ tree_offset2 = bit_position (field2);
+ tree_size2 = DECL_SIZE (field2);
+
+ if (!host_integerp (tree_offset1, 1)
+ || !host_integerp (tree_offset2, 1)
+ || !host_integerp (tree_size2, 1))
+ continue;
+
+ offset1 = TREE_INT_CST_LOW (tree_offset1);
+ offset2 = TREE_INT_CST_LOW (tree_offset2);
+ size2 = TREE_INT_CST_LOW (tree_size2);
+ align1 = DECL_ALIGN (field1) % param_align_bits;
+
+ if (offset1 % BITS_PER_UNIT != 0)
+ continue;
+
+ /* The two field references must fit within a block of memory that
+ is guaranteed to be on the same page. */
+ if (align1 + offset2 - offset1 + size2 > param_align_bits)
+ continue;
+
+ /* The two expressions cannot be dependent upon vdefs defined
+ in bb1/bb2. */
+ if (local_mem_dependence (def1, bb_for_def1)
+ || local_mem_dependence (def2, bb_for_def2))
+ continue;
+
+ /* The conditions are satisfied; hoist the loads from bb1 and bb2 into
+ bb0. We hoist the first one first so that a cache miss is handled
+ efficiently regardless of hardware cache-fill policy. */
+ 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",
+ bb_for_def1->index, bb_for_def2->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 and the target machine has
+ a conditional move instruction. */
+
+static bool
+gate_hoist_loads (void)
+{
+ return (flag_hoist_adjacent_loads == 1 && HAVE_conditional_move);
+}
+
/* Always do these optimizations if we have SSA
trees to work on. */
static bool
Index: gcc/common.opt
===================================================================
--- gcc/common.opt (revision 187805)
+++ 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) 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 187805)
+++ gcc/Makefile.in (working copy)
@@ -2355,7 +2355,8 @@ 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 187805)
+++ 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",
+ 32, 8, 256)
+
/*
Local variables:
mode:c
