[PATCH] Fix bogus -Wstringop-overflow warning

[Eric Botcazou via Gcc-patches]

Hi,

if you compile the attached testcase with -O2 -fno-inline -Wall, you get:

In function 'process_array3':
cc1: warning: 'process_array4' accessing 4 bytes in a region of size 3 [-
Wstringop-overflow=]
cc1: note: referencing argument 1 of type 'char[4]'
t.c:6:6: note: in a call to function 'process_array4'
    6 | void process_array4 (char a[4], int n)
      |      ^~~~~~~~~~~~~~
cc1: warning: 'process_array4' accessing 4 bytes in a region of size 3 [-
Wstringop-overflow=]
cc1: note: referencing argument 1 of type 'char[4]'
t.c:6:6: note: in a call to function 'process_array4'

That's because the ICF IPA pass has identified the two functions and turned 
process_array3 into a wrapper of process_array4.  This looks sensible to me 
given that the only difference between them is an "access" attribute on their 
type describing the access size of the parameter and the "access" attribute 
does not affect type identity (struct attribute_spec.affects_type_identity).

Hence the proposed fix, tested on x86-64/Linux, OK for the mainline?


2022-10-13  Eric Botcazou  <ebotca...@adacore.com>

        * gimple-ssa-warn-access.cc (pass_waccess::check_call): Return
        early for calls made from thunks.


2022-10-13  Eric Botcazou  <ebotca...@adacore.com>

        * gcc.dg/Wstringop-overflow-89.c: New test.

-- 
Eric Botcazou
diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
index 04aa849a4b1..59a70530600 100644
--- a/gcc/gimple-ssa-warn-access.cc
+++ b/gcc/gimple-ssa-warn-access.cc
@@ -4291,14 +4291,18 @@ pass_waccess::check_pointer_uses (gimple *stmt, tree ptr,
 void
 pass_waccess::check_call (gcall *stmt)
 {
-  if (gimple_call_builtin_p (stmt, BUILT_IN_NORMAL))
-    check_builtin (stmt);
+  /* Skip special calls generated by the compiler.  */
+  if (gimple_call_from_thunk_p (stmt))
+    return;
 
   /* .ASAN_MARK doesn't access any vars, only modifies shadow memory.  */
   if (gimple_call_internal_p (stmt)
       && gimple_call_internal_fn (stmt) == IFN_ASAN_MARK)
     return;
 
+  if (gimple_call_builtin_p (stmt, BUILT_IN_NORMAL))
+    check_builtin (stmt);
+
   if (!m_early_checks_p)
     if (tree callee = gimple_call_fndecl (stmt))
       {

/* { dg-do compile } */
/* { dg-options "-O2 -fno-inline -Wall" } */

extern void process (char);

void process_array4 (char a[4], int n)
{
  for (int i = 0; i < n; i++)
    process (a[i]);
}

void process_array3 (char a[3], int n)
{
  for (int i = 0; i < n; i++)
    process (a[i]);
}