[PATCH] Fold &MEM[0 + CST]->a.b.c to a constant

[Richard Biener]

This canonicalizes those to a constant literal.

Bootstrap / regtest running on x86_64-unknown-linux-gnu.

2020-05-11  Richard Biener  <rguent...@suse.de>

        * gimple-fold.c (maybe_canonicalize_mem_ref_addr): Canonicalize
        literal constant &MEM[..] to a constant literal.
---
 gcc/gimple-fold.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c
index 55b78fa284f..e4507877a0c 100644
--- a/gcc/gimple-fold.c
+++ b/gcc/gimple-fold.c
@@ -4840,6 +4840,7 @@ static bool
 maybe_canonicalize_mem_ref_addr (tree *t)
 {
   bool res = false;
+  tree *orig_t = t;
 
   if (TREE_CODE (*t) == ADDR_EXPR)
     t = &TREE_OPERAND (*t, 0);
@@ -4940,6 +4941,28 @@ maybe_canonicalize_mem_ref_addr (tree *t)
        }
     }
 
+  else if (TREE_CODE (*orig_t) == ADDR_EXPR
+          && TREE_CODE (*t) == MEM_REF
+          && TREE_CODE (TREE_OPERAND (*t, 0)) == INTEGER_CST)
+    {
+      tree base;
+      poly_int64 coffset;
+      base = get_addr_base_and_unit_offset (TREE_OPERAND (*orig_t, 0),
+                                           &coffset);
+      if (base)
+       {
+         gcc_assert (TREE_CODE (base) == MEM_REF);
+         poly_int64 moffset;
+         if (mem_ref_offset (base).to_shwi (&moffset))
+           {
+             coffset += moffset;
+             coffset += tree_to_poly_int64 (TREE_OPERAND (base, 0));
+             *orig_t = build_int_cst (TREE_TYPE (*orig_t), coffset);
+             return true;
+           }
+       }
+    }
+
   /* Canonicalize TARGET_MEM_REF in particular with respect to
      the indexes becoming constant.  */
   else if (TREE_CODE (*t) == TARGET_MEM_REF)
-- 
2.16.4