[PATCH 1/2] c++: Correct the handling of alignof(expr) [PR88115]

Patrick Palka ppalka@redhat.com
Wed Nov 11 18:21:32 GMT 2020


We're currently neglecting to set the ALIGNOF_EXPR_STD_P flag on an
ALIGNOF_EXPR when its operand is an expression.  This leads to us
handling alignof(expr) as if it were written __alignof__(expr), and
returning the preferred alignment instead of the ABI alignment.  In the
testcase below, this causes the first and third static_assert to fail on
x86.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?  Would it be appropriate for backporting to the release branches?

gcc/cp/ChangeLog:

	PR c++/88115
	* cp-tree.h (cxx_sizeof_or_alignof_expr): Add bool parameter.
	* decl.c (fold_sizeof_expr): Pass false to
	cxx_sizeof_or_alignof_expr.
	* parser.c (cp_parser_unary_expression): Pass std_alignof to
	cxx_sizeof_or_alignof_expr.
	* pt.c (tsubst_copy): Pass false to cxx_sizeof_or_alignof_expr.
	(tsubst_copy_and_build): Pass std_alignof to
	cxx_sizeof_or_alignof_expr.
	* typeck.c (cxx_alignof_expr): Add std_alignof bool parameter
	and pass it to cxx_sizeof_or_alignof_type.  Set ALIGNOF_EXPR_STD_P
	appropriately.
	(cxx_sizeof_or_alignof_expr): Add std_alignof bool parameter
	and pass it to cxx_alignof_expr.  Assert op is either
	SIZEOF_EXPR or ALIGNOF_EXPR.

libcc1/ChangeLog:

	PR c++/88115
	* libcp1plugin.cc (plugin_build_unary_expr): Pass true to
	cxx_sizeof_or_alignof_expr.

gcc/testsuite/ChangeLog:

	PR c++/88115
	* g++.dg/cpp0x/alignof6.C: New test.
---
 gcc/cp/cp-tree.h                      |  2 +-
 gcc/cp/decl.c                         |  2 +-
 gcc/cp/parser.c                       |  4 ++--
 gcc/cp/pt.c                           |  3 ++-
 gcc/cp/typeck.c                       | 17 +++++++++++------
 gcc/testsuite/g++.dg/cpp0x/alignof6.C | 19 +++++++++++++++++++
 libcc1/libcp1plugin.cc                |  2 +-
 7 files changed, 37 insertions(+), 12 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/alignof6.C

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 230a1525c63..63724c0e84f 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7461,7 +7461,7 @@ extern int comp_cv_qualification		(const_tree, const_tree);
 extern int comp_cv_qualification		(int, int);
 extern int comp_cv_qual_signature		(tree, tree);
 extern tree cxx_sizeof_or_alignof_expr		(location_t, tree,
-						 enum tree_code, bool);
+						 enum tree_code, bool, bool);
 extern tree cxx_sizeof_or_alignof_type		(location_t, tree,
 						 enum tree_code, bool, bool);
 extern tree cxx_alignas_expr                    (tree);
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 42e704e7af2..c52111e329c 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -10335,7 +10335,7 @@ fold_sizeof_expr (tree t)
   else
     r = cxx_sizeof_or_alignof_expr (EXPR_LOCATION (t),
 				    TREE_OPERAND (t, 0), SIZEOF_EXPR,
-				    false);
+				    false, false);
   if (r == error_mark_node)
     r = size_one_node;
   return r;
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 36322812310..4f59fc48d0f 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -8335,8 +8335,8 @@ cp_parser_unary_expression (cp_parser *parser, cp_id_kind * pidk,
 			   "ISO C++ does not allow %<alignof%> "
 			   "with a non-type");
 
-		ret = cxx_sizeof_or_alignof_expr (compound_loc,
-						  operand, op, true);
+		ret = cxx_sizeof_or_alignof_expr (compound_loc, operand, op,
+						  std_alignof, true);
 	      }
 	    /* For SIZEOF_EXPR, just issue diagnostics, but keep
 	       SIZEOF_EXPR with the original operand.  */
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 6ba114c9da3..1a01fb96c69 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -16789,6 +16789,7 @@ tsubst_copy (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 	      else
 		return cxx_sizeof_or_alignof_expr (input_location,
 						   expanded, SIZEOF_EXPR,
+						   false,
                                                    complain & tf_error);
 	    }
 	  else
@@ -19731,7 +19732,7 @@ tsubst_copy_and_build (tree t,
 					  complain & tf_error);
 	else
 	  r = cxx_sizeof_or_alignof_expr (input_location,
-					  op1, TREE_CODE (t),
+					  op1, TREE_CODE (t), std_alignof,
 					  complain & tf_error);
 	if (TREE_CODE (t) == SIZEOF_EXPR && r != error_mark_node)
 	  {
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index 08e0c80f9b0..700e166ca66 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -1832,10 +1832,12 @@ cxx_sizeof_expr (location_t loc, tree e, tsubst_flags_t complain)
 /* Implement the __alignof keyword: Return the minimum required
    alignment of E, measured in bytes.  For VAR_DECL's and
    FIELD_DECL's return DECL_ALIGN (which can be set from an
-   "aligned" __attribute__ specification).  */
+   "aligned" __attribute__ specification).  STD_ALIGNOF acts
+   like in cxx_sizeof_or_alignof_type.  */
 
 static tree
-cxx_alignof_expr (location_t loc, tree e, tsubst_flags_t complain)
+cxx_alignof_expr (location_t loc, tree e, bool std_alignof,
+		  tsubst_flags_t complain)
 {
   tree t;
 
@@ -1848,6 +1850,7 @@ cxx_alignof_expr (location_t loc, tree e, tsubst_flags_t complain)
       TREE_SIDE_EFFECTS (e) = 0;
       TREE_READONLY (e) = 1;
       SET_EXPR_LOCATION (e, loc);
+      ALIGNOF_EXPR_STD_P (e) = std_alignof;
 
       return e;
     }
@@ -1900,23 +1903,25 @@ cxx_alignof_expr (location_t loc, tree e, tsubst_flags_t complain)
     }
   else
     return cxx_sizeof_or_alignof_type (loc, TREE_TYPE (e),
-				       ALIGNOF_EXPR, false,
+				       ALIGNOF_EXPR, std_alignof,
                                        complain & tf_error);
 
   return fold_convert_loc (loc, size_type_node, t);
 }
 
 /* Process a sizeof or alignof expression E with code OP where the operand
-   is an expression.  */
+   is an expression. STD_ALIGNOF acts like in cxx_sizeof_or_alignof_type.  */
 
 tree
 cxx_sizeof_or_alignof_expr (location_t loc, tree e, enum tree_code op,
-			    bool complain)
+			    bool std_alignof, bool complain)
 {
+  gcc_assert (op == SIZEOF_EXPR || op == ALIGNOF_EXPR);
   if (op == SIZEOF_EXPR)
     return cxx_sizeof_expr (loc, e, complain? tf_warning_or_error : tf_none);
   else
-    return cxx_alignof_expr (loc, e, complain? tf_warning_or_error : tf_none);
+    return cxx_alignof_expr (loc, e, std_alignof,
+			     complain? tf_warning_or_error : tf_none);
 }
 
 /*  Build a representation of an expression 'alignas(E).'  Return the
diff --git a/gcc/testsuite/g++.dg/cpp0x/alignof6.C b/gcc/testsuite/g++.dg/cpp0x/alignof6.C
new file mode 100644
index 00000000000..b1a463df030
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alignof6.C
@@ -0,0 +1,19 @@
+// PR c++/88115
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-Wno-pedantic" }
+
+// Verify the non-standard extension alignof(expr) behaves like
+// alignof(type) to yield the ABI alignment of the type, and that
+// __alignof__(expr) behaves like __alignof__(type) to yield the
+// preferred alignment of the type.
+
+static_assert(alignof(double{}) == alignof(double), "");
+static_assert(__alignof__(double{}) == __alignof__(double), "");
+
+template <class T>
+void f() {
+  static_assert(alignof(T{}) == alignof(T), "");
+  static_assert(__alignof__(T{}) == __alignof__(T), "");
+}
+
+template void f<double>();
diff --git a/libcc1/libcp1plugin.cc b/libcc1/libcp1plugin.cc
index 67a235f9095..648368353cb 100644
--- a/libcc1/libcp1plugin.cc
+++ b/libcc1/libcp1plugin.cc
@@ -2806,7 +2806,7 @@ plugin_build_unary_expr (cc1_plugin::connection *self,
     case SIZEOF_EXPR:
     case ALIGNOF_EXPR:
       result = cxx_sizeof_or_alignof_expr (input_location,
-					   op0, opcode, true);
+					   op0, opcode, true, true);
       break;
 
     case DELETE_EXPR:
-- 
2.29.2.227.ge4d83eee92



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