+2009-05-26 Richard Guenther <rguenther@suse.de>
+
+ Backport from mainline
+ 2008-12-12 Zdenek Dvorak <ook@ucw.cz>
+
+ PR tree-optimization/32044
+ * tree-scalar-evolution.h (expression_expensive_p): Declare.
+ * tree-scalar-evolution.c (expression_expensive_p): New function.
+ (scev_const_prop): Avoid introducing expensive expressions.
+ * tree-ssa-loop-ivopts.c (may_eliminate_iv): Ditto.
+
2009-05-23 Eric Botcazou <ebotcazou@adacore.com>
* doc/passes.texi: Standardize spelling of RTL, Tree and Tree SSA.
--- /dev/null
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-empty -fdump-tree-final_cleanup" } */
+
+int foo (int n)
+{
+ while (n >= 45)
+ n -= 45;
+
+ return n;
+}
+
+int bar (int n)
+{
+ while (n >= 64)
+ n -= 64;
+
+ return n;
+}
+
+int bla (int n)
+{
+ int i = 0;
+
+ while (n >= 45)
+ {
+ i++;
+ n -= 45;
+ }
+
+ return i;
+}
+
+int baz (int n)
+{
+ int i = 0;
+
+ while (n >= 64)
+ {
+ i++;
+ n -= 64;
+ }
+
+ return i;
+}
+
+/* The loops computing division/modulo by 64 should be eliminated. */
+/* { dg-final { scan-tree-dump-times "Removing empty loop" 2 "empty" } } */
+
+/* There should be no division/modulo in the final dump (division and modulo
+ by 64 are done using bit operations). */
+/* { dg-final { scan-tree-dump-times "/" 0 "final_cleanup" } } */
+/* { dg-final { scan-tree-dump-times "%" 0 "final_cleanup" } } */
+
+/* { dg-final { cleanup-tree-dump "empty" } } */
+/* { dg-final { cleanup-tree-dump "final_cleanup" } } */
scalar_evolution_info = NULL;
}
+/* Returns true if the expression EXPR is considered to be too expensive
+ for scev_const_prop. */
+
+bool
+expression_expensive_p (tree expr)
+{
+ enum tree_code code;
+
+ if (is_gimple_val (expr))
+ return false;
+
+ code = TREE_CODE (expr);
+ if (code == TRUNC_DIV_EXPR
+ || code == CEIL_DIV_EXPR
+ || code == FLOOR_DIV_EXPR
+ || code == ROUND_DIV_EXPR
+ || code == TRUNC_MOD_EXPR
+ || code == CEIL_MOD_EXPR
+ || code == FLOOR_MOD_EXPR
+ || code == ROUND_MOD_EXPR
+ || code == EXACT_DIV_EXPR)
+ {
+ /* Division by power of two is usually cheap, so we allow it.
+ Forbid anything else. */
+ if (!integer_pow2p (TREE_OPERAND (expr, 1)))
+ return true;
+ }
+
+ switch (TREE_CODE_CLASS (code))
+ {
+ case tcc_binary:
+ case tcc_comparison:
+ if (expression_expensive_p (TREE_OPERAND (expr, 1)))
+ return true;
+
+ /* Fallthru. */
+ case tcc_unary:
+ return expression_expensive_p (TREE_OPERAND (expr, 0));
+
+ default:
+ return true;
+ }
+}
+
/* Replace ssa names for that scev can prove they are constant by the
appropriate constants. Also perform final value replacement in loops,
in case the replacement expressions are cheap.
continue;
niter = number_of_latch_executions (loop);
- /* We used to check here whether the computation of NITER is expensive,
- and avoided final value elimination if that is the case. The problem
- is that it is hard to evaluate whether the expression is too
- expensive, as we do not know what optimization opportunities the
- the elimination of the final value may reveal. Therefore, we now
- eliminate the final values of induction variables unconditionally. */
if (niter == chrec_dont_know)
continue;
/* Moving the computation from the loop may prolong life range
of some ssa names, which may cause problems if they appear
on abnormal edges. */
- || contains_abnormal_ssa_name_p (def))
+ || contains_abnormal_ssa_name_p (def)
+ /* Do not emit expensive expressions. The rationale is that
+ when someone writes a code like
+
+ while (n > 45) n -= 45;
+
+ he probably knows that n is not large, and does not want it
+ to be turned into n %= 45. */
+ || expression_expensive_p (def))
continue;
/* Eliminate the PHI node and replace it by a computation outside
projects / thirdparty / gcc.git / commitdiff
