https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77689
--- Comment #16 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
I am testing the following that makes loop splitting understand when first
iteration is special.
diff --git a/gcc/tree-ssa-loop-split.cc b/gcc/tree-ssa-loop-split.cc
index 70cd0aaefa7..1fd3ee1d1e5 100644
--- a/gcc/tree-ssa-loop-split.cc
+++ b/gcc/tree-ssa-loop-split.cc
@@ -42,6 +42,7 @@ along with GCC; see the file COPYING3. If not see
#include "gimple-fold.h"
#include "gimplify-me.h"
#include "print-tree.h"
+#include "value-query.h"
/* This file implements two kinds of loop splitting.
@@ -75,7 +76,8 @@ along with GCC; see the file COPYING3. If not see
point in *BORDER and the comparison induction variable in IV. */
static tree
-split_at_bb_p (class loop *loop, basic_block bb, tree *border, affine_iv *iv)
+split_at_bb_p (class loop *loop, basic_block bb, tree *border, affine_iv *iv,
+ enum tree_code *guard_code)
{
gcond *stmt;
affine_iv iv2;
@@ -87,19 +89,6 @@ split_at_bb_p (class loop *loop, basic_block bb, tree
*border, affine_iv *iv)
enum tree_code code = gimple_cond_code (stmt);
- /* Only handle relational comparisons, for equality and non-equality
- we'd have to split the loop into two loops and a middle statement. */
- switch (code)
- {
- case LT_EXPR:
- case LE_EXPR:
- case GT_EXPR:
- case GE_EXPR:
- break;
- default:
- return NULL_TREE;
- }
-
if (loop_exits_from_bb_p (loop, bb))
return NULL_TREE;
@@ -129,6 +118,55 @@ split_at_bb_p (class loop *loop, basic_block bb, tree
*border, affine_iv *iv)
if (!iv->no_overflow)
return NULL_TREE;
+ /* Only handle relational comparisons, for equality and non-equality
+ we'd have to split the loop into two loops and a middle statement. */
+ switch (code)
+ {
+ case LT_EXPR:
+ case LE_EXPR:
+ case GT_EXPR:
+ case GE_EXPR:
+ break;
+ case NE_EXPR:
+ case EQ_EXPR:
+ /* If the test check for first iteration, we can handle NE/EQ
+ with only one split loop. */
+ if (operand_equal_p (iv->base, iv2.base, 0))
+ {
+ if (code == EQ_EXPR)
+ code = !tree_int_cst_sign_bit (iv->step) ? LE_EXPR : GE_EXPR;
+ else
+ code = !tree_int_cst_sign_bit (iv->step) ? GT_EXPR : LT_EXPR;
+ break;
+ }
+ /* Similarly when the test checks for minimal or maximal
+ value range. */
+ else
+ {
+ int_range<2> r;
+ get_global_range_query ()->range_of_expr (r, op0, stmt);
+ if (!r.varying_p () && !r.undefined_p ())
+ {
+ wide_int val = wi::to_wide (op1);
+ if (known_eq (val, r.lower_bound ()))
+ {
+ code = (code == EQ_EXPR) ? LE_EXPR : GT_EXPR;
+ break;
+ }
+ else if (known_eq (val, r.upper_bound ()))
+ {
+ code = (code == EQ_EXPR) ? GE_EXPR : LT_EXPR;
+ break;
+ }
+ }
+ }
+ /* TODO: We can compare with exit condition; it seems that testing for
+ last iteration is common case. */
+ return NULL_TREE;
+ default:
+ return NULL_TREE;
+ }
+
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "Found potential split point: ");
@@ -143,6 +181,7 @@ split_at_bb_p (class loop *loop, basic_block bb, tree
*border, affine_iv *iv)
}
*border = iv2.base;
+ *guard_code = code;
return op0;
}
@@ -551,7 +590,7 @@ split_loop (class loop *loop1)
{
if (!niter.control.no_overflow)
return false;
- if (tree_int_cst_sign_bit (niter.control.step) > 0)
+ if (tree_int_cst_sign_bit (niter.control.step))
niter.cmp = GT_EXPR;
else
niter.cmp = LT_EXPR;
@@ -566,8 +605,9 @@ split_loop (class loop *loop1)
}
/* Find a splitting opportunity. */
+ enum tree_code guard_code;
for (i = 0; i < loop1->num_nodes; i++)
- if ((guard_iv = split_at_bb_p (loop1, bbs[i], &border, &iv)))
+ if ((guard_iv = split_at_bb_p (loop1, bbs[i], &border, &iv, &guard_code)))
{
profile_count entry_count = loop_preheader_edge (loop1)->count ();
/* Handling opposite steps is not implemented yet. Neither
@@ -585,7 +625,6 @@ split_loop (class loop *loop1)
gcond *guard_stmt = as_a<gcond *> (*gsi_last_bb (bbs[i]));
tree guard_init = PHI_ARG_DEF_FROM_EDGE (phi,
loop_preheader_edge (loop1));
- enum tree_code guard_code = gimple_cond_code (guard_stmt);
/* Loop splitting is implemented by versioning the loop, placing
the new loop after the old loop, make the first loop iterate
