https://gcc.gnu.org/g:b7c69cc072ef0da36439ebc55c513b48e68391b7
commit r15-5916-gb7c69cc072ef0da36439ebc55c513b48e68391b7
Author: Andrew Pinski <quic_apin...@quicinc.com>
Date: Mon Dec 2 08:35:23 2024 -0800
phiopt: Reset the number of iterations information of a loop when changing
an exit from the loop [PR117243]
After r12-5300-gf98f373dd822b3, phiopt could get the following bb structure:
|
middle-bb -----|
| |
| |----| |
phi<1, 2> | |
cond | |
| | |
|--------+---|
Which was considered 2 loops. The inner loop had esimtate of upper_bound to
be 8,
due to the original `for (b = 0; b <= 7; b++)`. The outer loop was already
an
infinite one.
So phiopt would come along and change the condition to be unconditionally
true,
we change the inner loop to being an infinite one but don't reset the
estimate
on the loop and cleanup cfg comes along and changes it into one loop but
also
does not reset the estimate of the loop. Then the loop unrolling uses the
old estimate
and decides to add an unreachable there.o
So the fix is when phiopt changes an exit to a loop, reset the estimates,
similar to
how cleanupcfg does it when merging some basic blocks.
Bootstrapped and tested on x86_64-linux-gnu.
PR tree-optimization/117243
PR tree-optimization/116749
gcc/ChangeLog:
* tree-ssa-phiopt.cc (replace_phi_edge_with_variable): Reset loop
estimates if the cond_block was an exit to a loop.
gcc/testsuite/ChangeLog:
* gcc.dg/torture/pr117243-1.c: New test.
* gcc.dg/torture/pr117243-2.c: New test.
Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com>
Diff:
---
gcc/testsuite/gcc.dg/torture/pr117243-1.c | 30 +++++++++++++++++++++++++++
gcc/testsuite/gcc.dg/torture/pr117243-2.c | 34 +++++++++++++++++++++++++++++++
gcc/tree-ssa-phiopt.cc | 11 ++++++++++
3 files changed, 75 insertions(+)
diff --git a/gcc/testsuite/gcc.dg/torture/pr117243-1.c
b/gcc/testsuite/gcc.dg/torture/pr117243-1.c
new file mode 100644
index 000000000000..c4bbc31467c5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr117243-1.c
@@ -0,0 +1,30 @@
+/* { dg-do compile } */
+/* { dg-options "-fdump-tree-optimized" } */
+/* { dg-skip-if "" { *-*-* } { "-fno-fat-lto-objects" } { "" } } */
+
+/* PR tree-optimization/117243 */
+/* foo should be an infinite but sometimes it gets optimized incorrectly into
+ an __builtin_unreachable(); which is not valid. */
+void
+foo (unsigned int a, unsigned char b)
+{
+ lbl:
+ for (b = 0; b <= 7; b++)
+ {
+ unsigned char c[1][1];
+ int i, j;
+ for (i = 0; i < 1; i++)
+ for (j = 0; j < 1; j++)
+ c[i][j] = 1;
+ if (b)
+ goto lbl;
+ }
+}
+
+int
+main ()
+{
+ foo (1, 2);
+}
+
+/* { dg-final { scan-tree-dump-not "__builtin_unreachable " "optimized"} } */
diff --git a/gcc/testsuite/gcc.dg/torture/pr117243-2.c
b/gcc/testsuite/gcc.dg/torture/pr117243-2.c
new file mode 100644
index 000000000000..d9b0d3eeb982
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr117243-2.c
@@ -0,0 +1,34 @@
+/* { dg-do compile } */
+/* { dg-options "-fno-tree-ch -fdump-tree-optimized" } */
+/* { dg-skip-if "" { *-*-* } { "-fno-fat-lto-objects" } { "" } } */
+
+/* PR tree-optimization/117243 */
+/* PR tree-optimization/116749 */
+
+/* main1 should be an infinite but sometimes it gets optimized incorrectly into
+ an __builtin_unreachable(); which is not valid. */
+int main1 (void)
+{
+ int g=0;
+ int l1[1];
+ int *l2 = &g;
+ int i;
+ for (i=0; i<1; i++)
+ l1[i] = (1);
+ for (g=0; g; ++g)
+ {
+ int *l3[1] = {&l1[0]};
+ }
+ *l2 = *l1;
+b:
+ for (i=0; i<2; ++i)
+ {
+ if (i)
+ goto b;
+ if (g)
+ continue;
+ }
+ return 0;
+}
+
+/* { dg-final { scan-tree-dump-not "__builtin_unreachable " "optimized"} } */
diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index 15651809d71b..d7b7c7467c19 100644
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -55,6 +55,7 @@ along with GCC; see the file COPYING3. If not see
#include "tree-ssa-propagate.h"
#include "tree-ssa-dce.h"
#include "calls.h"
+#include "tree-ssa-loop-niter.h"
/* Return the singleton PHI in the SEQ of PHIs for edges E0 and E1. */
@@ -152,6 +153,16 @@ replace_phi_edge_with_variable (basic_block cond_block,
else
gcc_unreachable ();
+ /* If we are removing the cond on a loop exit,
+ reset number of iteration information of the loop. */
+ if (loop_exits_from_bb_p (cond_block->loop_father, cond_block))
+ {
+ auto loop = cond_block->loop_father;
+ free_numbers_of_iterations_estimates (loop);
+ loop->any_upper_bound = false;
+ loop->any_likely_upper_bound = false;
+ }
+
if (edge_to_remove && EDGE_COUNT (edge_to_remove->dest->preds) == 1)
{
e->flags |= EDGE_FALLTHRU;
