[gcc r12-7439] warn-access: Fix up check_pointer_uses [PR104715]

[gcc r12-7439] warn-access: Fix up check_pointer_uses [PR104715]

[Jakub Jelinek]

https://gcc.gnu.org/g:1a0e3bba4b735fa8e4463d52950d0ce9c30c16c7

commit r12-7439-g1a0e3bba4b735fa8e4463d52950d0ce9c30c16c7
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Mar 1 21:05:31 2022 +0100

    warn-access: Fix up check_pointer_uses [PR104715]
    
    The following testcase emits bogus -Wdangling-pointer warnings.
    The bug is that when it sees that ptr immediate use is a call that
    returns one of its arguments, it will assume that the return value
    is based on ptr, but that is the case only if ptr is passed to the
    argument that is actually returned (so e.g. for memcpy the first argument,
    etc.).  When the builtins guarantee e.g. that the result is based on the
    first argument (either ERF_RETURNS_ARG 0 in which case it will always
    just returns the first argument as is, or when it is something like
    strstr or strpbrk or mempcpy that it returns some pointer based on the
    first argument), it means the result is not based on second or following
    argument if any.  The second hunk fixes this.
    
    The first hunk just removes an unnecessary TREE_CODE check, the code only
    pushes SSA_NAMEs into the pointers vector and if it didn't, it uses
          FOR_EACH_IMM_USE_FAST (use_p, iter, ptr)
    a few lines below this, which of course requires that ptr is a SSA_NAME.
    Tree checking on SSA_NAME_VERSION will already ensure that if it wasn't
    a SSA_NAME, we'd ICE.
    
    2022-03-01  Jakub Jelinek  <jakub@redhat.com>
    
            PR tree-optimization/104715
            * gimple-ssa-warn-access.cc (pass_waccess::check_pointer_uses): Don't
            unnecessarily test if ptr is a SSA_NAME, it has to be.  Only push lhs
            of a call if gimple_call_return_arg is equal to ptr, not just when it
            is non-NULL.
    
            * c-c++-common/Wdangling-pointer-7.c: New test.

Diff:
---
 gcc/gimple-ssa-warn-access.cc                    |  5 ++--
 gcc/testsuite/c-c++-common/Wdangling-pointer-7.c | 36 ++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
index d015c73dfc6..b7cdad517b3 100644
--- a/gcc/gimple-ssa-warn-access.cc
+++ b/gcc/gimple-ssa-warn-access.cc
@@ -4169,8 +4169,7 @@ pass_waccess::check_pointer_uses (gimple *stmt, tree ptr,
   for (unsigned i = 0; i != pointers.length (); ++i)
     {
       tree ptr = pointers[i];
-      if (TREE_CODE (ptr) == SSA_NAME
-	  && !bitmap_set_bit (visited, SSA_NAME_VERSION (ptr)))
+      if (!bitmap_set_bit (visited, SSA_NAME_VERSION (ptr)))
 	/* Avoid revisiting the same pointer.  */
 	continue;
 
@@ -4267,7 +4266,7 @@ pass_waccess::check_pointer_uses (gimple *stmt, tree ptr,
 
 	  if (gcall *call = dyn_cast <gcall *>(use_stmt))
 	    {
-	      if (gimple_call_return_arg (call))
+	      if (gimple_call_return_arg (call) == ptr)
 		if (tree lhs = gimple_call_lhs (call))
 		  if (TREE_CODE (lhs) == SSA_NAME)
 		    pointers.safe_push (lhs);
diff --git a/gcc/testsuite/c-c++-common/Wdangling-pointer-7.c b/gcc/testsuite/c-c++-common/Wdangling-pointer-7.c
new file mode 100644
index 00000000000..8423d3b01ad
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wdangling-pointer-7.c
@@ -0,0 +1,36 @@
+/* PR tree-optimization/104715 */
+/* { dg-do compile } */
+/* { dg-options "-Wdangling-pointer" } */
+
+char *
+foo (char *p)
+{
+  {
+    char q[61] = "012345678901234567890123456789012345678901234567890123456789";
+    char *r = q;
+    p = __builtin_strcat (p, r);
+  }
+  return p;	/* { dg-bogus "using dangling pointer" } */
+}
+
+char *
+bar (char *p)
+{
+  {
+    char q[] = "0123456789";
+    char *r = q;
+    p = __builtin_strstr (p, r);
+  }
+  return p;	/* { dg-bogus "using dangling pointer" } */
+}
+
+char *
+baz (char *p)
+{
+  {
+    char q[] = "0123456789";
+    char *r = q;
+    p = __builtin_strpbrk (p, r);
+  }
+  return p;	/* { dg-bogus "using dangling pointer" } */
+}