[committed] Fix a buglet in store merging (PR tree-optimization/83086)

[Jakub Jelinek]

Hi!

During the first loop iteration, n is uninitialized, so testing
n.base_addr is wrong.  Testing
(i == first ? this_n.base_addr : n.base_addr) is overkill,
perform_symbolic_merge will fail if some iterations have base_addr
set and others don't.

Bootstrapped/regtested on x86_64-linux and i686-linux, committed to trunk as
obvious.

2017-11-21  Jakub Jelinek  <ja...@redhat.com>

        PR tree-optimization/83086
        * gimple-ssa-store-merging.c
        (imm_store_chain_info::try_coalesce_bswap): Test this_n.base_addr
        rather than n.base_addr.

--- gcc/gimple-ssa-store-merging.c.jj   2017-11-21 09:41:00.000000000 +0100
+++ gcc/gimple-ssa-store-merging.c      2017-11-21 12:13:23.346947756 +0100
@@ -2390,7 +2390,7 @@ imm_store_chain_info::try_coalesce_bswap
                            ? try_size - info->bitsize - bitpos
                            : bitpos))
        return false;
-      if (n.base_addr && vuse_store)
+      if (this_n.base_addr && vuse_store)
        {
          unsigned int j;
          for (j = first; j <= last; ++j)

        Jakub