Hi,
This patch is to fix PR68529. In my previous scev/niter overflow patches, I
only computed no-overflow information for control iv in simple loops with
LT_EXPR as exit condition code. This bug is about loop with NE_EXPR as exit
condition code. Given below example:
#include <stdio.h>
#include <stdlib.h>
int main(){
char c[10000]={};
unsigned int nchar=9999;
while(nchar--!=0){
c[nchar]='A';
}
printf("%s\n",c);
return 0;
}
nchar used as an index to array 'c' doesn't overflow during loop iterations.
Thus &c[nchar] acts as a scev. GCC now fails to do that. With this patch,
this issue is fixed.
Furthermore, the computation of no-overflow information could be improved by
using TREE_OVERFLOW_UNDEFINED semantic of signed type for C/C++. I didn't
do that because:
1) I doubt how useful it could be because I have already changed scev to use
the semantic whenever possible. It doesn't need loop niter analysis' help.
2) To do that, I need to expose chrec_convert_aggressive information out of
scev in function simple_iv, because that function could corrupt
TREE_OVERFLOW_UNDEFINED semantic assumption. This isn't appropriate for
Stage3.
Bootstrap and test on x86_64 and x86. I don't expect any issue on aarch64
either. Is it OK?
2015-11-27 Bin Cheng <bin.ch...@arm.com>
PR tree-optimization/68529
* tree-ssa-loop-niter.c (number_of_iterations_ne): Add new param.
Compute no-overflow information for control iv.
(number_of_iterations_lt, number_of_iterations_le): Add new param.
(number_of_iterations_cond): Pass new argument to above functions.
2015-11-27 Bin Cheng <bin.ch...@arm.com>
PR tree-optimization/68529
* gcc.dg/tree-ssa/pr68529-1.c: New test.
* gcc.dg/tree-ssa/pr68529-2.c: New test.
* gcc.dg/tree-ssa/pr68529-3.c: New test.
Index: gcc/testsuite/gcc.dg/tree-ssa/pr68529-1.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pr68529-1.c (revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/pr68529-1.c (working copy)
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftree-loop-distribution -ftree-loop-distribute-patterns
-fdump-tree-ldist-details" } */
+
+void bar(char *s);
+int foo()
+{
+ char c[10000] = {};
+ unsigned short nchar = 9999;
+
+ while(nchar-- != 0)
+ {
+ c[nchar] = 'A';
+ }
+
+ bar (c);
+ return 0;
+}
+
+/* { dg-final { scan-tree-dump "distributed: split to 0 loops and 1 library
calls" "ldist" } } */
+/* { dg-final { scan-tree-dump "generated memset" "ldist" } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/pr68529-2.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pr68529-2.c (revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/pr68529-2.c (working copy)
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftree-loop-distribution -ftree-loop-distribute-patterns
-fdump-tree-ldist-details" } */
+
+void bar(char *s);
+int foo(unsigned short l)
+{
+ char c[10000] = {};
+ unsigned short nchar = 9999;
+
+ if (nchar <= l)
+ return -1;
+
+ while(nchar-- != l)
+ {
+ c[nchar] = 'A';
+ }
+
+ bar (c);
+ return 0;
+}
+
+/* { dg-final { scan-tree-dump "distributed: split to 0 loops and 1 library
calls" "ldist" } } */
+/* { dg-final { scan-tree-dump "generated memset" "ldist" } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/pr68529-3.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pr68529-3.c (revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/pr68529-3.c (working copy)
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftree-loop-distribution -ftree-loop-distribute-patterns
-fdump-tree-ldist-details" } */
+
+void bar(char *s);
+int foo(unsigned short l)
+{
+ char c[10000] = {};
+ unsigned short nchar = 9999;
+
+ if (nchar < l)
+ return -1;
+
+ while(nchar-- != l)
+ {
+ c[nchar] = 'A';
+ }
+
+ bar (c);
+ return 0;
+}
+
+/* { dg-final { scan-tree-dump "failed: evolution of offset is not affine"
"ldist" } } */
Index: gcc/tree-ssa-loop-niter.c
===================================================================
--- gcc/tree-ssa-loop-niter.c (revision 230945)
+++ gcc/tree-ssa-loop-niter.c (working copy)
@@ -957,13 +957,14 @@ number_of_iterations_ne_max (mpz_t bnd, bool no_ov
bounds on the difference FINAL - IV->base. */
static bool
-number_of_iterations_ne (tree type, affine_iv *iv, tree final,
- struct tree_niter_desc *niter, bool exit_must_be_taken,
- bounds *bnds)
+number_of_iterations_ne (struct loop *loop, tree type, affine_iv *iv,
+ tree final, struct tree_niter_desc *niter,
+ bool exit_must_be_taken, bounds *bnds)
{
tree niter_type = unsigned_type_for (type);
tree s, c, d, bits, assumption, tmp, bound;
mpz_t max;
+ tree e;
niter->control = *iv;
niter->bound = final;
@@ -998,6 +999,23 @@ static bool
TYPE_SIGN (niter_type));
mpz_clear (max);
+ /* Compute no-overflow information for the control iv. Note we are
+ handling NE_EXPR, if iv base equals to final value, the loop exits
+ immediately, and the iv does not overflow. */
+ if (tree_int_cst_sign_bit (iv->step))
+ e = fold_build2 (GE_EXPR, boolean_type_node, iv->base, final);
+ else
+ e = fold_build2 (LE_EXPR, boolean_type_node, iv->base, final);
+ e = simplify_using_initial_conditions (loop, e);
+ if (integer_onep (e)
+ && (integer_onep (s)
+ || (TREE_CODE (c) == INTEGER_CST
+ && TREE_CODE (s) == INTEGER_CST
+ && wi::mod_trunc (c, s, TYPE_SIGN (type)) == 0)))
+ {
+ niter->control.no_overflow = true;
+ }
+
/* First the trivial cases -- when the step is 1. */
if (integer_onep (s))
{
@@ -1361,8 +1379,8 @@ assert_loop_rolls_lt (tree type, affine_iv *iv0, a
that the exit must be taken eventually. */
static bool
-number_of_iterations_lt (tree type, affine_iv *iv0, affine_iv *iv1,
- struct tree_niter_desc *niter,
+number_of_iterations_lt (struct loop *loop, tree type, affine_iv *iv0,
+ affine_iv *iv1, struct tree_niter_desc *niter,
bool exit_must_be_taken, bounds *bnds)
{
tree niter_type = unsigned_type_for (type);
@@ -1434,7 +1452,8 @@ static bool
zps does not overflow. */
zps.no_overflow = true;
- return number_of_iterations_ne (type, &zps, delta, niter, true, bnds);
+ return number_of_iterations_ne (loop, type, &zps,
+ delta, niter, true, bnds);
}
/* Make sure that the control iv does not overflow. */
@@ -1473,9 +1492,9 @@ static bool
is the case). BNDS bounds the difference IV1->base - IV0->base. */
static bool
-number_of_iterations_le (tree type, affine_iv *iv0, affine_iv *iv1,
- struct tree_niter_desc *niter, bool exit_must_be_taken,
- bounds *bnds)
+number_of_iterations_le (struct loop *loop, tree type, affine_iv *iv0,
+ affine_iv *iv1, struct tree_niter_desc *niter,
+ bool exit_must_be_taken, bounds *bnds)
{
tree assumption;
tree type1 = type;
@@ -1523,7 +1542,7 @@ static bool
bounds_add (bnds, 1, type1);
- return number_of_iterations_lt (type, iv0, iv1, niter, exit_must_be_taken,
+ return number_of_iterations_lt (loop, type, iv0, iv1, niter,
exit_must_be_taken,
bnds);
}
@@ -1698,18 +1717,18 @@ number_of_iterations_cond (struct loop *loop,
{
case NE_EXPR:
gcc_assert (integer_zerop (iv1->step));
- ret = number_of_iterations_ne (type, iv0, iv1->base, niter,
+ ret = number_of_iterations_ne (loop, type, iv0, iv1->base, niter,
exit_must_be_taken, &bnds);
break;
case LT_EXPR:
- ret = number_of_iterations_lt (type, iv0, iv1, niter, exit_must_be_taken,
- &bnds);
+ ret = number_of_iterations_lt (loop, type, iv0, iv1, niter,
+ exit_must_be_taken, &bnds);
break;
case LE_EXPR:
- ret = number_of_iterations_le (type, iv0, iv1, niter, exit_must_be_taken,
- &bnds);
+ ret = number_of_iterations_le (loop, type, iv0, iv1, niter,
+ exit_must_be_taken, &bnds);
break;
default:
