On 7/22/19 10:26 PM, JiangNing OS wrote:
This patch is to fix PR91195. Is it OK for trunk?
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 711a31ea597..4db36644160 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2019-07-22 Jiangning Liu <jiangning....@amperecomputing.com>
+
+ PR middle-end/91195
+ * tree-ssa-phiopt.c (cond_store_replacement): Work around
+ -Wmaybe-uninitialized warning.
+
2019-07-22 Stafford Horne <sho...@gmail.com>
* config/or1k/or1k.c (or1k_expand_compare): Check for int before
diff --git a/gcc/tree-ssa-phiopt.c b/gcc/tree-ssa-phiopt.c
index b64bde695f4..7a86007d087 100644
--- a/gcc/tree-ssa-phiopt.c
+++ b/gcc/tree-ssa-phiopt.c
@@ -2240,6 +2240,14 @@ cond_store_replacement (basic_block middle_bb,
basic_block join_bb,
tree base = get_base_address (lhs);
if (!auto_var_p (base) || TREE_ADDRESSABLE (base))
return false;
+
+ /* The transformation below will inherently introduce a memory load,
+ for which LHS may not be initialized yet if it is not in NOTRAP,
+ so a -Wmaybe-uninitialized warning message could be triggered.
+ Since it's a bit hard to have a very accurate uninitialization
+ analysis to memory reference, we disable the warning here to avoid
+ confusion. */
+ TREE_NO_WARNING (lhs) = 1;
The no-warning bit is sometimes (typically?) set by the middle-end
after a warning has been issued, to avoid triggering other warnings
down the line for an already diagnosed expression. Unless it's
done just for the purposes of a single pass and the bit is cleared
afterwards, using it to avoid potential false positives doesn't
seem like a robust solution. It will mask warnings for constructs
that have been determined to be invalid.
FWIW, the middle-end is susceptible to quite a few false positives
that would nice to avoid. We have discussed various approaches to
the problem but setting the no-warning bit seems like too blunt of
an instrument.
Martin
