While working with Martin L's bugfix/cleanup I came across a minor bug
in the DSE code.
Specifically it mis-handles references with negative offsets. Example
code can be found in gcc.dg/pr48335-4.c. Thankfully these are
relatively uncommon and we can just prune them from consideration
without having major missed-optimization concerns.
Bootstrapped & regression tested with and without Martin L's bugfixes.
Installing on the trunk.
JEff
commit 261fc575195492afbedce5ebd872a2a25fe6efb1
Author: law <law@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Thu Oct 12 18:09:11 2017 +0000
* tree-ssa-dse.c (valid_ao_ref_for_dse): Reject ao_refs with
negative offsets.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@253691
138bc75d-0d04-0410-961f-82ee72b054a4
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index dc17b705025..d5ee088e77f 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2017-10-12 Jeff Law <l...@redhat.com>
+
+ * tree-ssa-dse.c (valid_ao_ref_for_dse): Reject ao_refs with
+ negative offsets.
+
2017-10-12 Martin Sebor <mse...@redhat.com>
PR other/82301
diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c
index 6f58fffc693..87e2fce9ac5 100644
--- a/gcc/tree-ssa-dse.c
+++ b/gcc/tree-ssa-dse.c
@@ -131,6 +131,7 @@ valid_ao_ref_for_dse (ao_ref *ref)
&& ref->max_size != -1
&& ref->size != 0
&& ref->max_size == ref->size
+ && ref->offset >= 0
&& (ref->offset % BITS_PER_UNIT) == 0
&& (ref->size % BITS_PER_UNIT) == 0
&& (ref->size != -1));
