[gcc r12-5465] Canonicalize &MEM[ssa_n, CST] to ssa_n p+ CST in fold_stmt_1

[gcc r12-5465] Canonicalize &MEM[ssa_n, CST] to ssa_n p+ CST in fold_stmt_1

[Andrew Pinski]

https://gcc.gnu.org/g:911b633803dcbb298c98777e29fd260834c0d04a

commit r12-5465-g911b633803dcbb298c98777e29fd260834c0d04a
Author: Andrew Pinski <apinski@marvell.com>
Date:   Tue Nov 23 01:08:55 2021 +0000

    Canonicalize &MEM[ssa_n, CST] to ssa_n p+ CST in fold_stmt_1
    
    This is a new version of the patch to fix PR 102216.
    Instead of doing the canonicalization inside forwprop, Richi
    mentioned we should do it inside fold_stmt_1 and that is what
    this patch does.
    
            PR tree-optimization/102216
    
    gcc/ChangeLog:
    
            * gimple-fold.c (fold_stmt_1): Add canonicalization
            of "&MEM[ssa_n, CST]" to "ssa_n p+ CST", note this
            can only be done if !in_place.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/tree-ssa/pr102216-1.C: New test.
            * g++.dg/tree-ssa/pr102216-2.C: New test.

Diff:
---
 gcc/gimple-fold.c                          | 22 +++++++++++++++
 gcc/testsuite/g++.dg/tree-ssa/pr102216-1.C | 21 ++++++++++++++
 gcc/testsuite/g++.dg/tree-ssa/pr102216-2.C | 45 ++++++++++++++++++++++++++++++
 3 files changed, 88 insertions(+)

diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c
index ad9703ee471..73f090bb14c 100644
--- a/gcc/gimple-fold.c
+++ b/gcc/gimple-fold.c
@@ -6061,6 +6061,28 @@ fold_stmt_1 (gimple_stmt_iterator *gsi, bool inplace, tree (*valueize) (tree))
 	  if (REFERENCE_CLASS_P (*lhs)
 	      && maybe_canonicalize_mem_ref_addr (lhs))
 	    changed = true;
+	  /* Canonicalize &MEM[ssa_n, CST] to ssa_n p+ CST.
+	     This cannot be done in maybe_canonicalize_mem_ref_addr
+	     as the gimple now has two operands rather than one.
+	     The same reason why this can't be done in
+	     maybe_canonicalize_mem_ref_addr is the same reason why
+	     this can't be done inplace.  */
+	  if (!inplace && TREE_CODE (*rhs) == ADDR_EXPR)
+	    {
+	      tree inner = TREE_OPERAND (*rhs, 0);
+	      if (TREE_CODE (inner) == MEM_REF
+		  && TREE_CODE (TREE_OPERAND (inner, 0)) == SSA_NAME
+		  && TREE_CODE (TREE_OPERAND (inner, 1)) == INTEGER_CST)
+		{
+		  tree ptr = TREE_OPERAND (inner, 0);
+		  tree addon = TREE_OPERAND (inner, 1);
+		  addon = fold_convert (sizetype, addon);
+		  gimple_assign_set_rhs_with_ops (gsi, POINTER_PLUS_EXPR,
+						  ptr, addon);
+		  changed = true;
+		  stmt = gsi_stmt (*gsi);
+		}
+	    }
 	}
       else
 	{
diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr102216-1.C b/gcc/testsuite/g++.dg/tree-ssa/pr102216-1.C
new file mode 100644
index 00000000000..21f7f6797ff
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/pr102216-1.C
@@ -0,0 +1,21 @@
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+void link_error ();
+void g ()
+{
+  const char **language_names;
+
+  language_names = new const char *[6];
+
+  const char **language_names_p = language_names;
+
+  language_names_p++;
+  language_names_p++;
+  language_names_p++;
+
+  if ( (language_names_p) - (language_names+3) != 0)
+    link_error();
+  delete[] language_names;
+}
+/* We should have removed the link_error on the gimple level as GCC should
+   be able to tell that language_names_p is the same as language_names+3.  */
+/* { dg-final { scan-tree-dump-times "link_error" 0 "optimized" } } */
diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr102216-2.C b/gcc/testsuite/g++.dg/tree-ssa/pr102216-2.C
new file mode 100644
index 00000000000..8d351a9bad0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/pr102216-2.C
@@ -0,0 +1,45 @@
+/* { dg-options "-O2 -Wall" } */
+#include <algorithm>
+
+static inline bool
+compare_cstrings (const char *str1, const char *str2)
+{
+  return str1 < str2;
+}
+
+void
+add_set_language_command ()
+{
+  static const char **language_names;
+
+  language_names = new const char *[6];
+
+  language_names[0] = "auto";
+  language_names[1] = "local";
+  language_names[2] = "unknown";
+
+  const char **language_names_p = language_names;
+  /* language_names_p == &language_names[0].  */
+  language_names_p++;
+  /* language_names_p == &language_names[1].  */
+  language_names_p++;
+  /* language_names_p == &language_names[2].  */
+  language_names_p++;
+  /* language_names_p == &language_names[3].  */
+
+  const char **sort_begin;
+
+  if (0)
+    sort_begin = &language_names[3];
+  else
+    sort_begin = language_names_p;
+
+  language_names[3] = "";
+  language_names[4] = "";
+  language_names[5] = NULL;
+
+  /* There should be no warning associated with this std::sort as
+     sort_begin != &language_names[5] and GCC should be able to figure
+     that out.  */
+  std::sort (sort_begin, &language_names[5], compare_cstrings);
+}