c-family: Fix -Warray-compare warning ICE [PR115290]

The warning code uses %D to print the ARRAY_REF first operands.
That works in the most common case where those operands are decls, but
as can be seen on the following testcase, they can be other expressions
with array type.
Just changing %D to %E isn't enough, because then the diagnostics can
suggest something like
note: use '&(x) != 0 ? (int (*)[32])&a : (int (*)[32])&b[0] == &(y) != 0 ? (int (*)[32])&a : (int (*)[32])&b[0]' to compare the addresses
which is a bad suggestion, the %E printing doesn't know that the
warning code will want to add & before it and [0] after it.
So, the following patch adds ()s around the operand as well, but does
that only for non-decls, for decls keeps it as &arr[0] like before.

2024-06-17  Jakub Jelinek  <jakub@redhat.com>

	PR c/115290
	* c-warn.cc (do_warn_array_compare): Use %E rather than %D for
	printing op0 and op1; if those operands aren't decls, also print
	parens around them.

	* c-c++-common/Warray-compare-3.c: New test.

diff --git a/gcc/c-family/c-warn.cc b/gcc/c-family/c-warn.cc
index 7ddf6ea2ad8e8b5ab43cdd1af702bcb4b7d8a0cd..5e4fb7f0f0a94a4acb4fb3faada505a0ff1fa496 100644 (file)
--- a/gcc/c-family/c-warn.cc
+++ b/gcc/c-family/c-warn.cc
@@ -3832,11 +3832,16 @@ do_warn_array_compare (location_t location, tree_code code, tree op0, tree op1)
       /* C doesn't allow +arr.  */
       if (c_dialect_cxx ())
        inform (location, "use unary %<+%> which decays operands to pointers "
-               "or %<&%D[0] %s &%D[0]%> to compare the addresses",
-               op0, op_symbol_code (code), op1);
+               "or %<&%s%E%s[0] %s &%s%E%s[0]%> to compare the addresses",
+               DECL_P (op0) ? "" : "(", op0, DECL_P (op0) ? "" : ")",
+               op_symbol_code (code),
+               DECL_P (op1) ? "" : "(", op1, DECL_P (op1) ? "" : ")");
       else
-       inform (location, "use %<&%D[0] %s &%D[0]%> to compare the addresses",
-               op0, op_symbol_code (code), op1);
+       inform (location,
+               "use %<&%s%E%s[0] %s &%s%E%s[0]%> to compare the addresses",
+               DECL_P (op0) ? "" : "(", op0, DECL_P (op0) ? "" : ")",
+               op_symbol_code (code),
+               DECL_P (op1) ? "" : "(", op1, DECL_P (op1) ? "" : ")");
     }
 }
 

diff --git a/gcc/testsuite/c-c++-common/Warray-compare-3.c b/gcc/testsuite/c-c++-common/Warray-compare-3.c
new file mode 100644 (file)
index 0000000..4725aa2
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Warray-compare-3.c
@@ -0,0 +1,13 @@
+/* PR c/115290 */
+/* { dg-do compile } */
+/* { dg-options "-Warray-compare" } */
+
+int a[32][32], b[32][32];
+
+int
+foo (int x, int y)
+{
+  return (x ? a : b) == (y ? a : b); /* { dg-warning "comparison between two arrays" } */
+/* { dg-message "use '&\\\(\[^\n\r]*\\\)\\\[0\\\] == &\\\(\[^\n\r]*\\\)\\\[0\\\]' to compare the addresses" "" { target c } .-1 } */
+/* { dg-message "use unary '\\\+' which decays operands to pointers or '&\\\(\[^\n\r]*\\\)\\\[0\\\] == &\\\(\[^\n\r]*\\\)\\\[0\\\]' to compare the addresses" "" { target c++ } .-2 } */
+}