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tree-optimization/106860 - fix profile scaling in split_loop

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The following fixes a mistake in loop splitting which assumes loop
latches have a single predecessor and that edge is from the exit
test.  Instead work from the single exit edge we have to find the
edge towards the latch.

	PR tree-optimization/106860
	* tree-ssa-loop-split.cc (split_loop): Find the exit to
	latch edge from the loop exit edge instead of from the
	latch.  Verify we're going to find it.

	* g++.dg/opt/pr106860.C: New testcase.
This commit is contained in:
Richard Biener 2022-09-07 10:44:33 +02:00
parent d14514641d
commit 0386609923
2 changed files with 33 additions and 6 deletions
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23
gcc/testsuite/g++.dg/opt/pr106860.C Normal file
View file

@ -0,0 +1,23 @@
// { dg-do compile }
// { dg-options "-Ofast -ftrapv -fnon-call-exceptions -fno-tree-fre" }
static const int N = 12;
int nSlip;
int main ()
{
int i, j, k, fdot = 0;
int a[N][N];
for ( i = 1; i < nSlip; i++)
{
for ( j = i+1; j < nSlip; j++)
{
for ( k = 0; k < i; k++)
fdot += a[i][k] * a[k][j];
a[i][j] = a[i][j] - fdot;
}
}
return 0;
}

16
gcc/tree-ssa-loop-split.cc
View file

@ -531,16 +531,17 @@ split_loop (class loop *loop1)
tree guard_iv;
tree border = NULL_TREE;
affine_iv iv;
edge exit1;
if (!single_exit (loop1)
if (!(exit1 = single_exit (loop1))
|| EDGE_COUNT (exit1->src->succs) != 2
/* ??? We could handle non-empty latches when we split the latch edge
(not the exit edge), and put the new exit condition in the new block.
OTOH this executes some code unconditionally that might have been
skipped by the original exit before. */
|| !empty_block_p (loop1->latch)
|| !easy_exit_values (loop1)
|| !number_of_iterations_exit (loop1, single_exit (loop1), &niter,
false, true)
|| !number_of_iterations_exit (loop1, exit1, &niter, false, true)
|| niter.cmp == ERROR_MARK
/* We can't yet handle loops controlled by a != predicate. */
|| niter.cmp == NE_EXPR)
@ -644,10 +645,13 @@ split_loop (class loop *loop1)
fix_loop_bb_probability (loop1, loop2, true_edge, false_edge);
/* Fix first loop's exit probability after scaling. */
edge exit_to_latch1 = single_pred_edge (loop1->latch);
edge exit_to_latch1;
if (EDGE_SUCC (exit1->src, 0) == exit1)
exit_to_latch1 = EDGE_SUCC (exit1->src, 1);
else
exit_to_latch1 = EDGE_SUCC (exit1->src, 0);
exit_to_latch1->probability *= true_edge->probability;
single_exit (loop1)->probability
= exit_to_latch1->probability.invert ();
exit1->probability = exit_to_latch1->probability.invert ();
/* Finally patch out the two copies of the condition to be always
true/false (or opposite). */