189 lines
5.8 KiB
Diff
189 lines
5.8 KiB
Diff
Index: gcc-4.3.2/gcc/tree-scalar-evolution.c
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===================================================================
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--- gcc-4.3.2.orig/gcc/tree-scalar-evolution.c 2009-01-28 10:14:37.000000000 +0100
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+++ gcc-4.3.2/gcc/tree-scalar-evolution.c 2009-01-28 10:17:50.000000000 +0100
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@@ -2716,6 +2716,50 @@
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scalar_evolution_info = NULL;
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}
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+/* Returns true if the expression EXPR is considered to be too expensive
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+ for scev_const_prop. */
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+
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+bool
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+expression_expensive_p (tree expr)
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+{
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+ enum tree_code code;
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+
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+ if (is_gimple_val (expr))
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+ return false;
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+
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+ code = TREE_CODE (expr);
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+ if (code == TRUNC_DIV_EXPR
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+ || code == CEIL_DIV_EXPR
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+ || code == FLOOR_DIV_EXPR
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+ || code == ROUND_DIV_EXPR
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+ || code == TRUNC_MOD_EXPR
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+ || code == CEIL_MOD_EXPR
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+ || code == FLOOR_MOD_EXPR
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+ || code == ROUND_MOD_EXPR
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+ || code == EXACT_DIV_EXPR)
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+ {
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+ /* Division by power of two is usually cheap, so we allow it.
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+ Forbid anything else. */
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+ if (!integer_pow2p (TREE_OPERAND (expr, 1)))
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+ return true;
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+ }
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+
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+ switch (TREE_CODE_CLASS (code))
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+ {
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+ case tcc_binary:
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+ case tcc_comparison:
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+ if (expression_expensive_p (TREE_OPERAND (expr, 1)))
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+ return true;
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+
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+ /* Fallthru. */
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+ case tcc_unary:
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+ return expression_expensive_p (TREE_OPERAND (expr, 0));
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+
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+ default:
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+ return true;
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+ }
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+}
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+
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/* Replace ssa names for that scev can prove they are constant by the
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appropriate constants. Also perform final value replacement in loops,
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in case the replacement expressions are cheap.
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@@ -2802,12 +2846,6 @@
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continue;
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niter = number_of_latch_executions (loop);
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- /* We used to check here whether the computation of NITER is expensive,
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- and avoided final value elimination if that is the case. The problem
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- is that it is hard to evaluate whether the expression is too
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- expensive, as we do not know what optimization opportunities the
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- the elimination of the final value may reveal. Therefore, we now
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- eliminate the final values of induction variables unconditionally. */
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if (niter == chrec_dont_know)
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continue;
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@@ -2838,7 +2876,15 @@
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/* Moving the computation from the loop may prolong life range
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of some ssa names, which may cause problems if they appear
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on abnormal edges. */
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- || contains_abnormal_ssa_name_p (def))
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+ || contains_abnormal_ssa_name_p (def)
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+ /* Do not emit expensive expressions. The rationale is that
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+ when someone writes a code like
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+
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+ while (n > 45) n -= 45;
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+
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+ he probably knows that n is not large, and does not want it
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+ to be turned into n %= 45. */
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+ || expression_expensive_p (def))
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continue;
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/* Eliminate the PHI node and replace it by a computation outside
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Index: gcc-4.3.2/gcc/tree-scalar-evolution.h
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===================================================================
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--- gcc-4.3.2.orig/gcc/tree-scalar-evolution.h 2009-01-28 10:22:47.000000000 +0100
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+++ gcc-4.3.2/gcc/tree-scalar-evolution.h 2009-01-28 10:23:10.000000000 +0100
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@@ -35,6 +35,7 @@
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extern void scev_analysis (void);
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unsigned int scev_const_prop (void);
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+bool expression_expensive_p (tree);
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extern bool simple_iv (struct loop *, tree, tree, affine_iv *, bool);
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/* Returns the loop of the polynomial chrec CHREC. */
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Index: gcc-4.3.2/gcc/testsuite/gcc.dg/pr34027-1.c
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===================================================================
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--- gcc-4.3.2.orig/gcc/testsuite/gcc.dg/pr34027-1.c 2009-01-28 10:24:09.000000000 +0100
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+++ gcc-4.3.2/gcc/testsuite/gcc.dg/pr34027-1.c 2009-01-28 10:24:43.000000000 +0100
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@@ -8,5 +8,9 @@
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return ns;
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}
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-/* { dg-final { scan-tree-dump "ns % 10000" "optimized" } } */
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+/* This test was originally introduced to test that we transform
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+ to ns % 10000. See the discussion of PR 32044 why we do not do
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+ that anymore. */
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+/* { dg-final { scan-tree-dump-times "%" 0 "optimized" } } */
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+/* { dg-final { scan-tree-dump-times "/" 0 "optimized" } } */
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/* { dg-final { cleanup-tree-dump "optimized" } } */
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Index: gcc-4.3.2/gcc/testsuite/gcc.dg/tree-ssa/pr32044.c
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===================================================================
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--- /dev/null 1970-01-01 00:00:00.000000000 +0000
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+++ gcc-4.3.2/gcc/testsuite/gcc.dg/tree-ssa/pr32044.c 2009-01-28 10:25:50.000000000 +0100
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@@ -0,0 +1,55 @@
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+/* { dg-do compile } */
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+/* { dg-options "-O2 -fdump-tree-empty -fdump-tree-final_cleanup" } */
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+
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+int foo (int n)
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+{
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+ while (n >= 45)
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+ n -= 45;
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+
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+ return n;
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+}
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+
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+int bar (int n)
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+{
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+ while (n >= 64)
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+ n -= 64;
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+
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+ return n;
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+}
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+
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+int bla (int n)
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+{
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+ int i = 0;
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+
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+ while (n >= 45)
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+ {
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+ i++;
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+ n -= 45;
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+ }
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+
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+ return i;
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+}
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+
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+int baz (int n)
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+{
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+ int i = 0;
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+
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+ while (n >= 64)
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+ {
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+ i++;
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+ n -= 64;
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+ }
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+
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+ return i;
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+}
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+
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+/* The loops computing division/modulo by 64 should be eliminated. */
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+/* { dg-final { scan-tree-dump-times "Removing empty loop" 2 "empty" } } */
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+
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+/* There should be no division/modulo in the final dump (division and modulo
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+ by 64 are done using bit operations). */
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+/* { dg-final { scan-tree-dump-times "/" 0 "final_cleanup" } } */
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+/* { dg-final { scan-tree-dump-times "%" 0 "final_cleanup" } } */
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+
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+/* { dg-final { cleanup-tree-dump "empty" } } */
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+/* { dg-final { cleanup-tree-dump "final_cleanup" } } */
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Index: gcc-4.3.2/gcc/tree-ssa-loop-ivopts.c
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===================================================================
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--- gcc-4.3.2.orig/gcc/tree-ssa-loop-ivopts.c 2009-01-28 10:26:04.000000000 +0100
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+++ gcc-4.3.2/gcc/tree-ssa-loop-ivopts.c 2009-01-28 10:27:09.000000000 +0100
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@@ -3778,7 +3778,12 @@
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return false;
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cand_value_at (loop, cand, use->stmt, nit, &bnd);
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+
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*bound = aff_combination_to_tree (&bnd);
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+ /* It is unlikely that computing the number of iterations using division
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+ would be more profitable than keeping the original induction variable. */
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+ if (expression_expensive_p (*bound))
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+ return false;
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return true;
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}
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