CSE negated multiplications and divisions

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.

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-88.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-88.c
new file mode 100644 (file)
index 0000000..15d2ca0
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-88.c
@@ -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" } } */

diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index 8fbb1dd..64f1e8c 100644 (file)
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -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)))