[gcc r11-8600] Backported from trunk:

[Martin Sebor <msebor@gcc.gnu.org>]

https://gcc.gnu.org/g:c2791cd4e62731ccde165c0e62b83f8e7ee38118

commit r11-8600-gc2791cd4e62731ccde165c0e62b83f8e7ee38118
Author: Martin Sebor <msebor@redhat.com>
Date:   Thu Jun 17 10:24:34 2021 -0600

    Backported from trunk:
    
    PR middle-end/100307 - spurious -Wplacement-new with negative pointer offset
    
    gcc/ChangeLog:
    
            PR middle-end/100307
            * builtins.c (compute_objsize_r): Clear base0 for pointers.
    
    gcc/testsuite/ChangeLog:
    
            PR middle-end/100307
            * g++.dg/warn/Wplacement-new-size-9.C: New test.
            * gcc.dg/tree-ssa/builtin-sprintf-warn-26.c: New test.

Diff:
---
 gcc/builtins.c                                     |  4 ++-
 gcc/testsuite/g++.dg/warn/Wplacement-new-size-9.C  | 39 ++++++++++++++++++++++
 .../gcc.dg/tree-ssa/builtin-sprintf-warn-26.c      | 38 +++++++++++++++++++++
 3 files changed, 80 insertions(+), 1 deletion(-)

diff --git a/gcc/builtins.c b/gcc/builtins.c
index 308846ee39b..1bfffe7081b 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -5451,8 +5451,10 @@ compute_objsize_r (tree ptr, int ostype, access_ref *pref,
       if (!addr && POINTER_TYPE_P (TREE_TYPE (ptr)))
 	{
 	  /* Set the maximum size if the reference is to the pointer
-	     itself (as opposed to what it points to).  */
+	     itself (as opposed to what it points to), and clear
+	     BASE0 since the offset isn't necessarily zero-based.  */
 	  pref->set_max_size_range ();
+	  pref->base0 = false;
 	  return true;
 	}
 
diff --git a/gcc/testsuite/g++.dg/warn/Wplacement-new-size-9.C b/gcc/testsuite/g++.dg/warn/Wplacement-new-size-9.C
new file mode 100644
index 00000000000..a6b5870be64
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wplacement-new-size-9.C
@@ -0,0 +1,39 @@
+/* PR middle-end/100307 - spurious -Wplacement-new with negative pointer
+   offset
+   { dg-do compile }
+   { dg-options "-O0 -Wall" } */
+
+void* operator new (__SIZE_TYPE__, void *p) { return p; }
+void* operator new[] (__SIZE_TYPE__, void *p) { return p; }
+
+static char a[2];
+
+void* nowarn_scalar ()
+{
+  char* p = a + 1;
+  char *q = new (p - 1) char ();    // { dg-bogus "-Wplacement-new" }
+  return q;
+}
+
+
+void* nowarn_array ()
+{
+  char* p = a + 1;
+  char *q = new (p - 1) char[2];    // { dg-bogus "-Wplacement-new" }
+  return q;
+}
+
+void* warn_scalar ()
+{
+  char* p = a + 1;
+  char *q = new (p - 2) char ();    // { dg-warning "-Wplacement-new" "pr100325" { xfail *-*-* } }
+  return q;
+}
+
+
+void* warn_array ()
+{
+  char* p = a + 1;
+  char *q = new (p - 1) char[2];    // { dg-warning "-Wplacement-new" "pr100325" { xfail *-*-* } }
+  return q;
+}
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/builtin-sprintf-warn-26.c b/gcc/testsuite/gcc.dg/tree-ssa/builtin-sprintf-warn-26.c
new file mode 100644
index 00000000000..16a551d9c8d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/builtin-sprintf-warn-26.c
@@ -0,0 +1,38 @@
+/* PR middle-end/100307 - spurious -Wplacement-new with negative pointer
+   offset
+   { dg-do compile }
+   { dg-options "-O0 -Wall" } */
+
+extern int sprintf (char*, const char*, ...);
+
+char a[4];
+
+void nowarn_1m1 ()
+{
+  char *p = a + 1;
+  sprintf (p - 1, "%i", 123);   // { dg-bogus "-Wformat-overflow" }
+}
+
+void nowarn_4m3 ()
+{
+  char *p = a + 4;
+  sprintf (p - 3, "%i", 12);    // { dg-bogus "-Wformat-overflow" }
+}
+
+void warn_2m1 ()
+{
+  char *p = a + 2;
+  sprintf (p - 1, "%i", 123);   // { dg-warning "-Wformat-overflow" "pr100325" { xfail *-*-* } }
+}
+
+void warn_3m1 ()
+{
+  char *p = a + 3;
+  sprintf (p - 1, "%i", 12);    // { dg-warning "-Wformat-overflow" "pr100325" { xfail *-*-* } }
+}
+
+void warn_4m1 ()
+{
+  char *p = a + 4;
+  sprintf (p - 1, "%i", 1);     // { dg-warning "-Wformat-overflow" "pr100325" { xfail *-*-* } }
+}