The following makes VRP deal better with the situation where the
same assertion is to be inserted on all predecessors of a BB.
That avoids the spurious array-bound warning (and enables some
optimization) when jump-threading f**ed up the CFG in such redundant
way.
(the fully "correct" way to deal with this VRP shortcoming is
to make assert insertion also insert PHIs for merges as there are
cases - such like this - where the merged range is useful; but
as comments say PHI insertion is expensive and via update-ssa
it is also quite excessive)
Bootstrap / regtest running on x86_64-unknown-linux-gnu.
Richard.
2017-01-16 Richard Biener <rguent...@suse.de>
PR tree-optimization/71433
* tree-vrp.c (register_new_assert_for): Merge same asserts
on all incoming edges.
(process_assert_insertions_for): Handle insertions at the
beginning of BBs.
* gcc.dg/Warray-bounds-20.c: New testcase.
Index: gcc/tree-vrp.c
===================================================================
--- gcc/tree-vrp.c (revision 244484)
+++ gcc/tree-vrp.c (working copy)
@@ -5032,6 +5032,17 @@ register_new_assert_for (tree name, tree
loc->si = si;
return;
}
+ /* If we have the same assertion on all incoming edges of a BB
+ instead insert it at the beginning of it. */
+ if (e && loc->e
+ && dest_bb == loc->e->dest
+ && EDGE_COUNT (dest_bb->preds) == 2)
+ {
+ loc->bb = dest_bb;
+ loc->e = NULL;
+ loc->si = gsi_none ();
+ return;
+ }
}
/* Update the last node of the list and move to the next one. */
@@ -6429,6 +6440,15 @@ process_assert_insertions_for (tree name
return true;
}
+ /* If the stmt iterator points at the end then this is an insertion
+ at the beginning of a block. */
+ if (gsi_end_p (loc->si))
+ {
+ gimple_stmt_iterator si = gsi_after_labels (loc->bb);
+ gsi_insert_before (&si, assert_stmt, GSI_SAME_STMT);
+ return false;
+
+ }
/* Otherwise, we can insert right after LOC->SI iff the
statement must not be the last statement in the block. */
stmt = gsi_stmt (loc->si);
Index: gcc/testsuite/gcc.dg/Warray-bounds-20.c
===================================================================
--- gcc/testsuite/gcc.dg/Warray-bounds-20.c (nonexistent)
+++ gcc/testsuite/gcc.dg/Warray-bounds-20.c (working copy)
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Warray-bounds" } */
+
+int t[1];
+int fct (int r, long e)
+{
+ int d = 0;
+ if (r == 4)
+ r = 1;
+ if (e < -52)
+ d = r == 0 ? 1 : 2;
+ else
+ {
+ int i, n = 53;
+ if (__builtin_expect (e < 0, 0))
+ n += e;
+ for (i = 1 ; i < n / 64 + 1 ; i++)
+ t[i] = 0; /* { dg-bogus "array bounds" } */
+ }
+ return d;
+}
