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CSE negated multiplications and divisions

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This adds the capability to look for available negated multiplications
and divisions, replacing them with cheaper negates.

2020-09-17  Richard Biener  <rguenther@suse.de>

	* tree-ssa-sccvn.c (visit_nary_op): Value-number multiplications
	and divisions to negates of available negated forms.

	* gcc.dg/tree-ssa/ssa-fre-88.c: New testcase.
This commit is contained in:
Richard Biener 2020-09-17 11:48:36 +02:00
parent 225a08220e
commit c7f4be78cb
2 changed files with 53 additions and 0 deletions
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18
gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-88.c Normal file
View file

@ -0,0 +1,18 @@
/* { dg-do compile } */
/* { dg-options "-O2 -fdump-tree-fre1" } */
double y[2];
void foo (double x)
{
y[0] = x * -3.;
y[1] = x * 3.;
}
void bar (double x, double z)
{
y[0] = -z / x;
y[1] = z / x;
}
/* { dg-final { scan-tree-dump-times " \\* " 1 "fre1" } } */
/* { dg-final { scan-tree-dump-times " / " 1 "fre1" } } */
/* { dg-final { scan-tree-dump-times "= -_" 2 "fre1" } } */

35
gcc/tree-ssa-sccvn.c
View file

@ -4824,6 +4824,40 @@ visit_nary_op (tree lhs, gassign *stmt)
}
}
break;
case RDIV_EXPR:
case TRUNC_DIV_EXPR:
case MULT_EXPR:
/* Match up ([-]a){/,*}([-])b with v=a{/,*}b, replacing it with -v. */
if (! HONOR_SIGN_DEPENDENT_ROUNDING (type))
{
tree rhs[2];
rhs[0] = rhs1;
rhs[1] = gimple_assign_rhs2 (stmt);
for (unsigned i = 0; i <= 1; ++i)
{
unsigned j = i == 0 ? 1 : 0;
tree ops[2];
gimple_match_op match_op (gimple_match_cond::UNCOND,
NEGATE_EXPR, type, rhs[i]);
ops[i] = vn_nary_build_or_lookup_1 (&match_op, false);
ops[j] = rhs[j];
if (ops[i]
&& (ops[0] = vn_nary_op_lookup_pieces (2, code,
type, ops, NULL)))
{
gimple_match_op match_op (gimple_match_cond::UNCOND,
NEGATE_EXPR, type, ops[0]);
result = vn_nary_build_or_lookup (&match_op);
if (result)
{
bool changed = set_ssa_val_to (lhs, result);
vn_nary_op_insert_stmt (stmt, result);
return changed;
}
}
}
}
break;
default:
break;
}
@ -5739,6 +5773,7 @@ eliminate_dom_walker::eliminate_insert (basic_block bb,
if (!stmt
|| (!CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (stmt))
&& gimple_assign_rhs_code (stmt) != VIEW_CONVERT_EXPR
&& gimple_assign_rhs_code (stmt) != NEGATE_EXPR
&& gimple_assign_rhs_code (stmt) != BIT_FIELD_REF
&& (gimple_assign_rhs_code (stmt) != BIT_AND_EXPR
|| TREE_CODE (gimple_assign_rhs2 (stmt)) != INTEGER_CST)))