[gcc r11-8964] middle-end/101824 - properly handle volatiles in nested fn lowering

[Richard Biener]

https://gcc.gnu.org/g:3f29e301f299a1b4e2c535affb964f0b97b7639c

commit r11-8964-g3f29e301f299a1b4e2c535affb964f0b97b7639c
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Aug 9 10:19:10 2021 +0200

    middle-end/101824 - properly handle volatiles in nested fn lowering
    
    When we build the COMPONENT_REF of a formerly volatile local off
    the FRAME decl we have to make sure to mark the COMPONENT_REF
    as TREE_THIS_VOLATILE.  While the GIMPLE operand scanner looks
    at the FIELD_DECL this is not how volatile GENERIC refs work.
    
    2021-08-09  Richard Biener  <rguenther@suse.de>
    
            PR middle-end/101824
            * tree-nested.c (get_frame_field): Mark the COMPONENT_REF as
            volatile in case the variable was.
    
            * gcc.dg/tree-ssa/pr101824.c: New testcase.
    
    (cherry picked from commit bb169406cdc9e044eaec500dd742c2fed40f5488)

Diff:
---
 gcc/testsuite/gcc.dg/tree-ssa/pr101824.c | 19 +++++++++++++++++++
 gcc/tree-nested.c                        |  1 +
 2 files changed, 20 insertions(+)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr101824.c b/gcc/testsuite/gcc.dg/tree-ssa/pr101824.c
new file mode 100644
index 00000000000..d5987e14360
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr101824.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fdump-tree-pcom-details -fdump-tree-optimized" } */
+
+int main()
+{
+  volatile int y;
+  void bar()
+    {
+      __builtin_printf ("%d", y);
+    }
+  while (y)
+    ;
+  return 0;
+}
+
+/* Make sure the load from y is correctly interpreted as volatile, even
+   when going through FRAME.  */
+/* { dg-final { scan-tree-dump-not "Executing predictive commoning" "pcom" } } */
+/* { dg-final { scan-tree-dump " ={v} FRAME" "optimized" } } */
diff --git a/gcc/tree-nested.c b/gcc/tree-nested.c
index cea917a4d58..968431fa22a 100644
--- a/gcc/tree-nested.c
+++ b/gcc/tree-nested.c
@@ -1033,6 +1033,7 @@ get_frame_field (struct nesting_info *info, tree target_context,
     }
 
   x = build3 (COMPONENT_REF, TREE_TYPE (field), x, field, NULL_TREE);
+  TREE_THIS_VOLATILE (x) = TREE_THIS_VOLATILE (field);
   return x;
 }