[Buildroot] gcc-4.3.2: add backport fix for PR 32044
Daniel Mack
daniel at caiaq.de
Tue Mar 10 01:06:00 UTC 2009
Hi,
gcc-4.3.2 needs a backported patch for issue PR 32044, below is a patch
that adds this to buildroot2.
Many thanks to Uwe Kleine-König for the backport and to Robert Schwebel
for pointing me there.
The original posting is here:
http://www.nabble.com/Backport-fix-for-PR-32044-(final-value-replacement-too-aggressive)-%09to-gcc-4.3-td22199271.html
Not sure yet whether this solves a number of strange crashes on a PXA
board, but the patch is certainly needed.
Best regards,
Daniel
Index: toolchain/gcc/4.3.2/901-backport-fix-for-bug-32044.patch
===================================================================
--- toolchain/gcc/4.3.2/901-backport-fix-for-bug-32044.patch (revision 0)
+++ toolchain/gcc/4.3.2/901-backport-fix-for-bug-32044.patch (revision 0)
@@ -0,0 +1,188 @@
+Index: gcc-4.3.2/gcc/tree-scalar-evolution.c
+===================================================================
+--- gcc-4.3.2.orig/gcc/tree-scalar-evolution.c 2009-01-28 10:14:37.000000000 +0100
++++ gcc-4.3.2/gcc/tree-scalar-evolution.c 2009-01-28 10:17:50.000000000 +0100
+@@ -2716,6 +2716,50 @@
+ 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.
+@@ -2802,12 +2846,6 @@
+ 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;
+
+@@ -2838,7 +2876,15 @@
+ /* 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
+Index: gcc-4.3.2/gcc/tree-scalar-evolution.h
+===================================================================
+--- gcc-4.3.2.orig/gcc/tree-scalar-evolution.h 2009-01-28 10:22:47.000000000 +0100
++++ gcc-4.3.2/gcc/tree-scalar-evolution.h 2009-01-28 10:23:10.000000000 +0100
+@@ -35,6 +35,7 @@
+ extern void scev_analysis (void);
+ unsigned int scev_const_prop (void);
+
++bool expression_expensive_p (tree);
+ extern bool simple_iv (struct loop *, tree, tree, affine_iv *, bool);
+
+ /* Returns the loop of the polynomial chrec CHREC. */
+Index: gcc-4.3.2/gcc/testsuite/gcc.dg/pr34027-1.c
+===================================================================
+--- gcc-4.3.2.orig/gcc/testsuite/gcc.dg/pr34027-1.c 2009-01-28 10:24:09.000000000 +0100
++++ gcc-4.3.2/gcc/testsuite/gcc.dg/pr34027-1.c 2009-01-28 10:24:43.000000000 +0100
+@@ -8,5 +8,9 @@
+ return ns;
+ }
+
+-/* { dg-final { scan-tree-dump "ns % 10000" "optimized" } } */
++/* This test was originally introduced to test that we transform
++ to ns % 10000. See the discussion of PR 32044 why we do not do
++ that anymore. */
++/* { dg-final { scan-tree-dump-times "%" 0 "optimized" } } */
++/* { dg-final { scan-tree-dump-times "/" 0 "optimized" } } */
+ /* { dg-final { cleanup-tree-dump "optimized" } } */
+Index: gcc-4.3.2/gcc/testsuite/gcc.dg/tree-ssa/pr32044.c
+===================================================================
+--- /dev/null 1970-01-01 00:00:00.000000000 +0000
++++ gcc-4.3.2/gcc/testsuite/gcc.dg/tree-ssa/pr32044.c 2009-01-28 10:25:50.000000000 +0100
+@@ -0,0 +1,55 @@
++/* { 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" } } */
+Index: gcc-4.3.2/gcc/tree-ssa-loop-ivopts.c
+===================================================================
+--- gcc-4.3.2.orig/gcc/tree-ssa-loop-ivopts.c 2009-01-28 10:26:04.000000000 +0100
++++ gcc-4.3.2/gcc/tree-ssa-loop-ivopts.c 2009-01-28 10:27:09.000000000 +0100
+@@ -3778,7 +3778,12 @@
+ return false;
+
+ cand_value_at (loop, cand, use->stmt, nit, &bnd);
++
+ *bound = aff_combination_to_tree (&bnd);
++ /* It is unlikely that computing the number of iterations using division
++ would be more profitable than keeping the original induction variable. */
++ if (expression_expensive_p (*bound))
++ return false;
+ return true;
+ }
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