[gcc/devel/c++-modules] gimple: Ignore *0 = {CLOBBER} in path isolation [PR96722]

[Nathan Sidwell <nathan@gcc.gnu.org>]

https://gcc.gnu.org/g:a5b15fcb954ba63d58f0daa700281aba33b5f24a

commit a5b15fcb954ba63d58f0daa700281aba33b5f24a
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Aug 25 13:49:40 2020 +0200

    gimple: Ignore *0 = {CLOBBER} in path isolation [PR96722]
    
    Clobbers of MEM_REF with NULL address are just fancy nops, something we just
    ignore and don't emit any code for it (ditto for other clobbers), they just
    mark end of life on something, so we shouldn't infer from those that there
    is some UB.
    
    2020-08-25  Jakub Jelinek  <jakub@redhat.com>
    
            PR tree-optimization/96722
            * gimple.c (infer_nonnull_range): Formatting fix.
            (infer_nonnull_range_by_dereference): Return false for clobber stmts.
    
            * g++.dg/opt/pr96722.C: New test.

Diff:
---
 gcc/gimple.c                       |  7 ++++---
 gcc/testsuite/g++.dg/opt/pr96722.C | 20 ++++++++++++++++++++
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/gcc/gimple.c b/gcc/gimple.c
index 41f7cf38b1c..bf863f67ee2 100644
--- a/gcc/gimple.c
+++ b/gcc/gimple.c
@@ -2917,8 +2917,8 @@ check_loadstore (gimple *, tree op, tree, void *data)
 bool
 infer_nonnull_range (gimple *stmt, tree op)
 {
-  return infer_nonnull_range_by_dereference (stmt, op)
-    || infer_nonnull_range_by_attribute (stmt, op);
+  return (infer_nonnull_range_by_dereference (stmt, op)
+	  || infer_nonnull_range_by_attribute (stmt, op));
 }
 
 /* Return true if OP can be inferred to be non-NULL after STMT
@@ -2930,7 +2930,8 @@ infer_nonnull_range_by_dereference (gimple *stmt, tree op)
      non-NULL if -fdelete-null-pointer-checks is enabled.  */
   if (!flag_delete_null_pointer_checks
       || !POINTER_TYPE_P (TREE_TYPE (op))
-      || gimple_code (stmt) == GIMPLE_ASM)
+      || gimple_code (stmt) == GIMPLE_ASM
+      || gimple_clobber_p (stmt))
     return false;
 
   if (walk_stmt_load_store_ops (stmt, (void *)op,
diff --git a/gcc/testsuite/g++.dg/opt/pr96722.C b/gcc/testsuite/g++.dg/opt/pr96722.C
new file mode 100644
index 00000000000..408dfeea8a0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/pr96722.C
@@ -0,0 +1,20 @@
+// PR tree-optimization/96722
+// { dg-do run }
+// { dg-options "-O2" }
+
+struct S { int s; ~S () {} };
+
+void
+foo (S *a)
+{
+  if (a)
+    return;
+  a->~S ();
+}
+
+int
+main ()
+{
+  S s;
+  foo (&s);
+}