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Re: [PATCH] Hoist reciprocal invariant out of loop
Appended is the final version of the previously approved patch
that I checked in.
David
* tree-ssa-loop-im.c: Include real.h.
(determine_invariantness_stmt): If real division divisor is
invariant and flag_unsafe_math_optimizations enabled, generate
invariant reciprocal for hoisting.
* Makefile.in (tree-ssa-loop-im.o): Add real.h dependency.
Index: tree-ssa-loop-im.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-ssa-loop-im.c,v
retrieving revision 2.35
retrieving revision 2.36
diff -c -p -r2.35 -r2.36
*** tree-ssa-loop-im.c 9 Apr 2005 01:37:24 -0000 2.35
--- tree-ssa-loop-im.c 11 Apr 2005 20:17:38 -0000 2.36
*************** Software Foundation, 59 Temple Place - S
*** 37,42 ****
--- 37,43 ----
#include "params.h"
#include "tree-pass.h"
#include "flags.h"
+ #include "real.h"
/* TODO: Support for predicated code motion. I.e.
*************** determine_invariantness_stmt (struct dom
*** 562,568 ****
{
enum move_pos pos;
block_stmt_iterator bsi;
! tree stmt;
bool maybe_never = ALWAYS_EXECUTED_IN (bb) == NULL;
struct loop *outermost = ALWAYS_EXECUTED_IN (bb);
--- 563,569 ----
{
enum move_pos pos;
block_stmt_iterator bsi;
! tree stmt, rhs;
bool maybe_never = ALWAYS_EXECUTED_IN (bb) == NULL;
struct loop *outermost = ALWAYS_EXECUTED_IN (bb);
*************** determine_invariantness_stmt (struct dom
*** 588,593 ****
--- 589,635 ----
continue;
}
+ /* If divisor is invariant, convert a/b to a*(1/b), allowing reciprocal
+ to be hoisted out of loop, saving expensive divide. */
+ if (pos == MOVE_POSSIBLE
+ && (rhs = TREE_OPERAND (stmt, 1)) != NULL
+ && TREE_CODE (rhs) == RDIV_EXPR
+ && flag_unsafe_math_optimizations
+ && outermost_invariant_loop_expr (TREE_OPERAND (rhs, 1),
+ loop_containing_stmt (stmt)) != NULL
+ && outermost_invariant_loop_expr (rhs,
+ loop_containing_stmt (stmt)) == NULL)
+ {
+ tree lhs, stmt1, stmt2, var, name;
+
+ lhs = TREE_OPERAND (stmt, 0);
+
+ /* stmt must be MODIFY_EXPR. */
+ var = create_tmp_var (TREE_TYPE (rhs), "reciptmp");
+ add_referenced_tmp_var (var);
+
+ stmt1 = build2 (MODIFY_EXPR, void_type_node, var,
+ build2 (RDIV_EXPR, TREE_TYPE (rhs),
+ build_real (TREE_TYPE (rhs), dconst1),
+ TREE_OPERAND (rhs, 1)));
+ name = make_ssa_name (var, stmt1);
+ TREE_OPERAND (stmt1, 0) = name;
+ stmt2 = build2 (MODIFY_EXPR, void_type_node, lhs,
+ build2 (MULT_EXPR, TREE_TYPE (rhs),
+ name, TREE_OPERAND (rhs, 0)));
+
+ /* Replace division stmt with reciprocal and multiply stmts.
+ The multiply stmt is not invariant, so update iterator
+ and avoid rescanning. */
+ bsi_replace (&bsi, stmt1, true);
+ get_stmt_operands (stmt1); /* Should not be necessary. */
+ bsi_insert_after (&bsi, stmt2, BSI_NEW_STMT);
+ SSA_NAME_DEF_STMT (lhs) = stmt2;
+
+ /* Continue processing with invariant reciprocal statment. */
+ stmt = stmt1;
+ }
+
stmt_ann (stmt)->common.aux = xcalloc (1, sizeof (struct lim_aux_data));
LIM_DATA (stmt)->always_executed_in = outermost;