match.pd: Optimize MIN_EXPR <addr1, addr2> etc. addr1 < addr2 would be simplified [PR102951]

This patch outlines the decision whether address comparison can be folded
or not from the match.pd simple comparison simplification and uses it
both there and in a new minmax simplification, such that we fold e.g.
MAX (&a[2], &a[1]) etc.
Some of the Wstringop-overflow-62.c changes might look weird, but that
seems to be mainly due to gimple_fold_builtin_memset not bothering to
copy over location, will fix that incrementally.

2021-10-28  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/102951
	* fold-const.h (address_compare): Declare.
	* fold-const.c (address_compare): New function.
	* match.pd (cmp (convert1?@2 addr@0) (convert2? addr@1)): Use
	address_compare helper.
	(minmax cmp (convert1?@2 addr@0) (convert2?@3 addr@1)): New
	simplification.

	* gcc.dg/tree-ssa/pr102951.c: New test.
	* gcc.dg/Wstringop-overflow-62.c: Adjust expected diagnostics.

5 files changed, 220 insertions, 129 deletions

diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index c7daf871..54f91f0 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -16492,6 +16492,132 @@ tree_nonzero_bits (const_tree t)
   return wi::shwi (-1, TYPE_PRECISION (TREE_TYPE (t)));
 }
 
+/* Helper function for address compare simplifications in match.pd.
+   OP0 and OP1 are ADDR_EXPR operands being compared by CODE.
+   BASE0, BASE1, OFF0 and OFF1 are set by the function.
+   GENERIC is true if GENERIC folding and false for GIMPLE folding.
+   Returns 0 if OP0 is known to be unequal to OP1 regardless of OFF{0,1},
+   1 if bases are known to be equal and OP0 cmp OP1 depends on OFF0 cmp OFF1,
+   and 2 if unknown.  */
+
+int
+address_compare (tree_code code, tree type, tree op0, tree op1,
+		 tree &base0, tree &base1, poly_int64 &off0, poly_int64 &off1,
+		 bool generic)
+{
+  gcc_checking_assert (TREE_CODE (op0) == ADDR_EXPR);
+  gcc_checking_assert (TREE_CODE (op1) == ADDR_EXPR);
+  base0 = get_addr_base_and_unit_offset (TREE_OPERAND (op0, 0), &off0);
+  base1 = get_addr_base_and_unit_offset (TREE_OPERAND (op1, 0), &off1);
+  if (base0 && TREE_CODE (base0) == MEM_REF)
+    {
+      off0 += mem_ref_offset (base0).force_shwi ();
+      base0 = TREE_OPERAND (base0, 0);
+    }
+  if (base1 && TREE_CODE (base1) == MEM_REF)
+    {
+      off1 += mem_ref_offset (base1).force_shwi ();
+      base1 = TREE_OPERAND (base1, 0);
+    }
+  if (base0 == NULL_TREE || base1 == NULL_TREE)
+    return 2;
+
+  int equal = 2;
+  /* Punt in GENERIC on variables with value expressions;
+     the value expressions might point to fields/elements
+     of other vars etc.  */
+  if (generic
+      && ((VAR_P (base0) && DECL_HAS_VALUE_EXPR_P (base0))
+	  || (VAR_P (base1) && DECL_HAS_VALUE_EXPR_P (base1))))
+    return 2;
+  else if (decl_in_symtab_p (base0) && decl_in_symtab_p (base1))
+    {
+      symtab_node *node0 = symtab_node::get_create (base0);
+      symtab_node *node1 = symtab_node::get_create (base1);
+      equal = node0->equal_address_to (node1);
+    }
+  else if ((DECL_P (base0)
+	    || TREE_CODE (base0) == SSA_NAME
+	    || TREE_CODE (base0) == STRING_CST)
+	   && (DECL_P (base1)
+	       || TREE_CODE (base1) == SSA_NAME
+	       || TREE_CODE (base1) == STRING_CST))
+    equal = (base0 == base1);
+  if (equal == 1)
+    {
+      if (code == EQ_EXPR
+	  || code == NE_EXPR
+	  /* If the offsets are equal we can ignore overflow.  */
+	  || known_eq (off0, off1)
+	  || TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (op0))
+	  /* Or if we compare using pointers to decls or strings.  */
+	  || (POINTER_TYPE_P (type)
+	      && (DECL_P (base0) || TREE_CODE (base0) == STRING_CST)))
+	return 1;
+      return 2;
+    }
+  if (equal != 0)
+    return equal;
+  if (code != EQ_EXPR && code != NE_EXPR)
+    return 2;
+
+  HOST_WIDE_INT ioff0 = -1, ioff1 = -1;
+  off0.is_constant (&ioff0);
+  off1.is_constant (&ioff1);
+  if ((DECL_P (base0) && TREE_CODE (base1) == STRING_CST)
+       || (TREE_CODE (base0) == STRING_CST && DECL_P (base1))
+       || (TREE_CODE (base0) == STRING_CST
+	   && TREE_CODE (base1) == STRING_CST
+	   && ioff0 >= 0 && ioff1 >= 0
+	   && ioff0 < TREE_STRING_LENGTH (base0)
+	   && ioff1 < TREE_STRING_LENGTH (base1)
+	  /* This is a too conservative test that the STRING_CSTs
+	     will not end up being string-merged.  */
+	   && strncmp (TREE_STRING_POINTER (base0) + ioff0,
+		       TREE_STRING_POINTER (base1) + ioff1,
+		       MIN (TREE_STRING_LENGTH (base0) - ioff0,
+			    TREE_STRING_LENGTH (base1) - ioff1)) != 0))
+    ;
+  else if (!DECL_P (base0) || !DECL_P (base1))
+    return 2;
+  /* If this is a pointer comparison, ignore for now even
+     valid equalities where one pointer is the offset zero
+     of one object and the other to one past end of another one.  */
+  else if (!INTEGRAL_TYPE_P (type))
+    ;
+  /* Assume that automatic variables can't be adjacent to global
+     variables.  */
+  else if (is_global_var (base0) != is_global_var (base1))
+    ;
+  else
+    {
+      tree sz0 = DECL_SIZE_UNIT (base0);
+      tree sz1 = DECL_SIZE_UNIT (base1);
+      /* If sizes are unknown, e.g. VLA or not representable, punt.  */
+      if (!tree_fits_poly_int64_p (sz0) || !tree_fits_poly_int64_p (sz1))
+	return 2;
+
+      poly_int64 size0 = tree_to_poly_int64 (sz0);
+      poly_int64 size1 = tree_to_poly_int64 (sz1);
+      /* If one offset is pointing (or could be) to the beginning of one
+	 object and the other is pointing to one past the last byte of the
+	 other object, punt.  */
+      if (maybe_eq (off0, 0) && maybe_eq (off1, size1))
+	equal = 2;
+      else if (maybe_eq (off1, 0) && maybe_eq (off0, size0))
+	equal = 2;
+      /* If both offsets are the same, there are some cases we know that are
+	 ok.  Either if we know they aren't zero, or if we know both sizes
+	 are no zero.  */
+      if (equal == 2
+	  && known_eq (off0, off1)
+	  && (known_ne (off0, 0)
+	      || (known_ne (size0, 0) && known_ne (size1, 0))))
+	equal = 0;
+     }
+  return equal;
+}
+
 #if CHECKING_P
 
 namespace selftest {
diff --git a/gcc/fold-const.h b/gcc/fold-const.h
index 7bac84b..fed4768 100644
--- a/gcc/fold-const.h
+++ b/gcc/fold-const.h
@@ -213,6 +213,8 @@ extern bool negate_mathfn_p (combined_fn);
 extern const char *getbyterep (tree, unsigned HOST_WIDE_INT *);
 extern const char *c_getstr (tree);
 extern wide_int tree_nonzero_bits (const_tree);
+extern int address_compare (tree_code, tree, tree, tree, tree &, tree &,
+			    poly_int64 &, poly_int64 &, bool);
 
 /* Return OFF converted to a pointer offset type suitable as offset for
    POINTER_PLUS_EXPR.  Use location LOC for this conversion.  */
diff --git a/gcc/match.pd b/gcc/match.pd
index 43d1c1b..0734c45 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3009,6 +3009,30 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
     @0
     @2)))
 
+/* Simplify min (&var[off0], &var[off1]) etc. depending on whether
+   the addresses are known to be less, equal or greater.  */
+(for minmax (min max)
+     cmp (lt gt)
+ (simplify
+  (minmax (convert1?@2 addr@0) (convert2?@3 addr@1))
+  (with
+   {
+     poly_int64 off0, off1;
+     tree base0, base1;
+     int equal = address_compare (cmp, TREE_TYPE (@2), @0, @1, base0, base1,
+				  off0, off1, GENERIC);
+   }
+   (if (equal == 1)
+    (if (minmax == MIN_EXPR)
+     (if (known_le (off0, off1))
+      @2
+      (if (known_gt (off0, off1))
+       @3))
+     (if (known_ge (off0, off1))
+      @2
+      (if (known_lt (off0, off1))
+       @3)))))))
+
 /* (convert (minmax ((convert (x) c)))) -> minmax (x c) if x is promoted
    and the outer convert demotes the expression back to x's type.  */
 (for minmax (min max)
@@ -5291,132 +5315,30 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
   (with
    {
      poly_int64 off0, off1;
-     tree base0 = get_addr_base_and_unit_offset (TREE_OPERAND (@0, 0), &off0);
-     tree base1 = get_addr_base_and_unit_offset (TREE_OPERAND (@1, 0), &off1);
-     if (base0 && TREE_CODE (base0) == MEM_REF)
-       {
-	 off0 += mem_ref_offset (base0).force_shwi ();
-         base0 = TREE_OPERAND (base0, 0);
-       }
-     if (base1 && TREE_CODE (base1) == MEM_REF)
-       {
-	 off1 += mem_ref_offset (base1).force_shwi ();
-         base1 = TREE_OPERAND (base1, 0);
-       }
+     tree base0, base1;
+     int equal = address_compare (cmp, TREE_TYPE (@2), @0, @1, base0, base1,
+				  off0, off1, GENERIC);
    }
-   (if (base0 && base1)
-    (with
-     {
-       int equal = 2;
-       /* Punt in GENERIC on variables with value expressions;
-	  the value expressions might point to fields/elements
-	  of other vars etc.  */
-       if (GENERIC
-	   && ((VAR_P (base0) && DECL_HAS_VALUE_EXPR_P (base0))
-	       || (VAR_P (base1) && DECL_HAS_VALUE_EXPR_P (base1))))
-	 ;
-       else if (decl_in_symtab_p (base0)
-		&& decl_in_symtab_p (base1))
-         equal = symtab_node::get_create (base0)
-	           ->equal_address_to (symtab_node::get_create (base1));
-       else if ((DECL_P (base0)
-		 || TREE_CODE (base0) == SSA_NAME
-		 || TREE_CODE (base0) == STRING_CST)
-		&& (DECL_P (base1)
-		    || TREE_CODE (base1) == SSA_NAME
-		    || TREE_CODE (base1) == STRING_CST))
-         equal = (base0 == base1);
-       if (equal == 0)
-	 {
-	   HOST_WIDE_INT ioff0 = -1, ioff1 = -1;
-	   off0.is_constant (&ioff0);
-	   off1.is_constant (&ioff1);
-	   if ((DECL_P (base0) && TREE_CODE (base1) == STRING_CST)
-	       || (TREE_CODE (base0) == STRING_CST && DECL_P (base1))
-	       || (TREE_CODE (base0) == STRING_CST
-		   && TREE_CODE (base1) == STRING_CST
-		   && ioff0 >= 0 && ioff1 >= 0
-		   && ioff0 < TREE_STRING_LENGTH (base0)
-		   && ioff1 < TREE_STRING_LENGTH (base1)
-		   /* This is a too conservative test that the STRING_CSTs
-		      will not end up being string-merged.  */
-		   && strncmp (TREE_STRING_POINTER (base0) + ioff0,
-			       TREE_STRING_POINTER (base1) + ioff1,
-			       MIN (TREE_STRING_LENGTH (base0) - ioff0,
-				    TREE_STRING_LENGTH (base1) - ioff1)) != 0))
-	     ;
-	   else if (!DECL_P (base0) || !DECL_P (base1))
-	     equal = 2;
-	   else if (cmp != EQ_EXPR && cmp != NE_EXPR)
-	     equal = 2;
-	   /* If this is a pointer comparison, ignore for now even
-	      valid equalities where one pointer is the offset zero
-	      of one object and the other to one past end of another one.  */
-	   else if (!INTEGRAL_TYPE_P (TREE_TYPE (@2)))
-	     ;
-	   /* Assume that automatic variables can't be adjacent to global
-	      variables.  */
-	   else if (is_global_var (base0) != is_global_var (base1))
-	     ;
-	   else
-	     {
-	       tree sz0 = DECL_SIZE_UNIT (base0);
-	       tree sz1 = DECL_SIZE_UNIT (base1);
-	       /* If sizes are unknown, e.g. VLA or not representable,
-		  punt.  */
-	       if (!tree_fits_poly_int64_p (sz0)
-		   || !tree_fits_poly_int64_p (sz1))
-		 equal = 2;
-	       else
-		 {
-		   poly_int64 size0 = tree_to_poly_int64 (sz0);
-		   poly_int64 size1 = tree_to_poly_int64 (sz1);
-		   /* If one offset is pointing (or could be) to the beginning
-		      of one object and the other is pointing to one past the
-		      last byte of the other object, punt.  */
-		   if (maybe_eq (off0, 0) && maybe_eq (off1, size1))
-		     equal = 2;
-		   else if (maybe_eq (off1, 0) && maybe_eq (off0, size0))
-		     equal = 2;
-		   /* If both offsets are the same, there are some cases
-		      we know that are ok.  Either if we know they aren't
-		      zero, or if we know both sizes are no zero.  */
-		   if (equal == 2
-		       && known_eq (off0, off1)
-		       && (known_ne (off0, 0)
-			   || (known_ne (size0, 0) && known_ne (size1, 0))))
-		     equal = 0;
-		 }
-	     }
-	 }
-     }
-     (if (equal == 1
-	  && (cmp == EQ_EXPR || cmp == NE_EXPR
-	      /* If the offsets are equal we can ignore overflow.  */
-	      || known_eq (off0, off1)
-	      || TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@0))
-		 /* Or if we compare using pointers to decls or strings.  */
-	      || (POINTER_TYPE_P (TREE_TYPE (@2))
-		  && (DECL_P (base0) || TREE_CODE (base0) == STRING_CST))))
-      (switch
-       (if (cmp == EQ_EXPR && (known_eq (off0, off1) || known_ne (off0, off1)))
-	{ constant_boolean_node (known_eq (off0, off1), type); })
-       (if (cmp == NE_EXPR && (known_eq (off0, off1) || known_ne (off0, off1)))
-	{ constant_boolean_node (known_ne (off0, off1), type); })
-       (if (cmp == LT_EXPR && (known_lt (off0, off1) || known_ge (off0, off1)))
-	{ constant_boolean_node (known_lt (off0, off1), type); })
-       (if (cmp == LE_EXPR && (known_le (off0, off1) || known_gt (off0, off1)))
-	{ constant_boolean_node (known_le (off0, off1), type); })
-       (if (cmp == GE_EXPR && (known_ge (off0, off1) || known_lt (off0, off1)))
-	{ constant_boolean_node (known_ge (off0, off1), type); })
-       (if (cmp == GT_EXPR && (known_gt (off0, off1) || known_le (off0, off1)))
-	{ constant_boolean_node (known_gt (off0, off1), type); }))
-      (if (equal == 0)
-	(switch
-	 (if (cmp == EQ_EXPR)
-	  { constant_boolean_node (false, type); })
-	 (if (cmp == NE_EXPR)
-	  { constant_boolean_node (true, type); })))))))))
+   (if (equal == 1)
+    (switch
+     (if (cmp == EQ_EXPR && (known_eq (off0, off1) || known_ne (off0, off1)))
+      { constant_boolean_node (known_eq (off0, off1), type); })
+     (if (cmp == NE_EXPR && (known_eq (off0, off1) || known_ne (off0, off1)))
+      { constant_boolean_node (known_ne (off0, off1), type); })
+     (if (cmp == LT_EXPR && (known_lt (off0, off1) || known_ge (off0, off1)))
+      { constant_boolean_node (known_lt (off0, off1), type); })
+     (if (cmp == LE_EXPR && (known_le (off0, off1) || known_gt (off0, off1)))
+      { constant_boolean_node (known_le (off0, off1), type); })
+     (if (cmp == GE_EXPR && (known_ge (off0, off1) || known_lt (off0, off1)))
+      { constant_boolean_node (known_ge (off0, off1), type); })
+     (if (cmp == GT_EXPR && (known_gt (off0, off1) || known_le (off0, off1)))
+      { constant_boolean_node (known_gt (off0, off1), type); }))
+    (if (equal == 0)
+     (switch
+      (if (cmp == EQ_EXPR)
+       { constant_boolean_node (false, type); })
+      (if (cmp == NE_EXPR)
+       { constant_boolean_node (true, type); })))))))
 
 /* Simplify pointer equality compares using PTA.  */
 (for neeq (ne eq)
diff --git a/gcc/testsuite/gcc.dg/Wstringop-overflow-62.c b/gcc/testsuite/gcc.dg/Wstringop-overflow-62.c
index 4b6d1ab..e39ab2f 100644
--- a/gcc/testsuite/gcc.dg/Wstringop-overflow-62.c
+++ b/gcc/testsuite/gcc.dg/Wstringop-overflow-62.c
@@ -217,14 +217,14 @@ void test_max (void)
   {
     /* Exercise both pointers pointing to the same object plus constant
        offset.  */
-    char a2[2];               // { dg-message "at offset 1 into destination object 'a2' of size 2" "note" }
+    char a2[2];
     char *pi = a2 + 1;
     char *pj = a2 + 2;
 
     char *q = MAX (pi, pj);
 
-    memset (q, 0, 1);
-    memset (q, 0, 2);         // { dg-warning "writing 2 bytes into a region of size 1 " }
+    memset (q, 0, 1);         // { dg-warning "writing 1 byte into a region of size 0 " "" { target *-*-* } 0 }
+    memset (q, 0, 2);         // { dg-warning "writing 2 bytes into a region of size 0 " }
   }
 
   {
@@ -345,7 +345,7 @@ void test_max (void)
        not reflected in the determaxed offset).  */
     char *q = MAX (p1, p2);
 
-    memset (q, 0, 1);         // { dg-warning "writing 1 byte into a region of size 0 " }
+    memset (q, 0, 1);
   }
 
   {
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr102951.c b/gcc/testsuite/gcc.dg/tree-ssa/pr102951.c
new file mode 100644
index 0000000..42b6fe6
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr102951.c
@@ -0,0 +1,41 @@
+/* PR tree-optimization/102951 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-ccp1" } */
+/* { dg-final { scan-tree-dump-times "return \&a\\\[1\\\];" 2 "ccp1" } } */
+/* { dg-final { scan-tree-dump-times "return \&a\\\[4\\\];" 2 "ccp1" } } */
+/* { dg-final { scan-tree-dump-not "MIN_EXPR" "ccp1" } } */
+/* { dg-final { scan-tree-dump-not "MAX_EXPR" "ccp1" } } */
+
+extern int a[5];
+
+int *
+foo (void)
+{
+  int *p1 = &a[1];
+  int *p2 = &a[2];
+  return p1 < p2 ? p1 : p2;
+}
+
+int *
+bar (void)
+{
+  int *p1 = &a[1];
+  int *p2 = &a[2];
+  return p1 <= p2 ? p1 : p2;
+}
+
+int *
+baz (void)
+{
+  int *p1 = &a[3];
+  int *p2 = &a[4];
+  return p1 > p2 ? p1 : p2;
+}
+
+int *
+qux (void)
+{
+  int *p1 = &a[3];
+  int *p2 = &a[4];
+  return p1 >= p2 ? p1 : p2;
+}