Re: [PATCH] middle-end/100464 - avoid spurious TREE_ADDRESSABLE in folding debug stmts

[Jason Merrill via Gcc-patches]

On 5/7/21 6:21 AM, Richard Biener wrote:
On Fri, May 7, 2021 at 12:17 PM Richard Biener <rguent...@suse.de> wrote:

canonicalize_constructor_val was setting TREE_ADDRESSABLE on bases
of ADDR_EXPRs but that's futile when we're dealing with CTOR values
in debug stmts.  This rips out the code which was added for Java
and should have been an assertion when we didn't have debug stmts.

Bootstrapped and tested on x86_64-unknown-linux-gnu for all languages
which revealed PR100468 for which I added the cp/class.c hunk below.
Re-testing with that in progress.

OK for trunk and branch?  It looks like this C++ code is new in GCC 11.

I mislooked, the code is old.

This hunk also breaks (or fixes) g++.dg/tree-ssa/array-temp1.C where
the gimplifier previously passes the

            && (flag_merge_constants >= 2 || !TREE_ADDRESSABLE (object))

check guarding it against unifying addresses of different instances
of variables.  Clearly in the case of the testcase there are addresses to
this variable as part of the initializer list construction.  So the hunk fixes
wrong-code, but it breaks the testcase.

Any comments?  I can of course change the testcase accordingly.

Hmm, I suppose if the optimization is wrong for PR38615, it's also wrong 
for the initializer_list variant:

extern "C" void abort (void);
#include <initializer_list>

int f(int t, const int *a)
{
  std::initializer_list<int> b = { 1, 2, 3 };
  const int *p = b.begin();
  if (!t)
    return f (1, p);
 return p == a;
}

int main(void)
{
 if (f(0, 0))
   abort ();
 return 0;
}

so adjusting the array-temp testcase seems like the right answer.

Thanks,
Richard.

2021-05-07  Richard Biener  <rguent...@suse.de>

         PR middle-end/100464
         PR c++/100468
gcc/
         * gimple-fold.c (canonicalize_constructor_val): Do not set
         TREE_ADDRESSABLE.

gcc/cp/
         * call.c (set_up_extended_ref_temp): Mark the temporary
         addressable if the TARGET_EXPR was.

gcc/testsuite/
         * gcc.dg/pr100464.c: New testcase.
---
  gcc/cp/call.c                   |  2 ++
  gcc/gimple-fold.c               |  4 +++-
  gcc/testsuite/gcc.dg/pr100464.c | 16 ++++++++++++++++
  3 files changed, 21 insertions(+), 1 deletion(-)
  create mode 100644 gcc/testsuite/gcc.dg/pr100464.c

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 57bac05fe70..ea97be22f07 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -12478,6 +12478,8 @@ set_up_extended_ref_temp (tree decl, tree expr, vec<tree, 
va_gc> **cleanups,
       VAR.  */
    if (TREE_CODE (expr) != TARGET_EXPR)
      expr = get_target_expr (expr);
+  else if (TREE_ADDRESSABLE (expr))
+    TREE_ADDRESSABLE (var) = 1;

    if (TREE_CODE (decl) == FIELD_DECL
        && extra_warnings && !TREE_NO_WARNING (decl))
diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c
index aa33779b753..768ef89d876 100644
--- a/gcc/gimple-fold.c
+++ b/gcc/gimple-fold.c
@@ -245,7 +245,9 @@ canonicalize_constructor_val (tree cval, tree from_decl)
        if (TREE_TYPE (base) == error_mark_node)
         return NULL_TREE;
        if (VAR_P (base))
-       TREE_ADDRESSABLE (base) = 1;
+       /* ???  We should be able to assert that TREE_ADDRESSABLE is set,
+          but since the use can be in a debug stmt we can't.  */
+       ;
        else if (TREE_CODE (base) == FUNCTION_DECL)
         {
           /* Make sure we create a cgraph node for functions we'll reference.
diff --git a/gcc/testsuite/gcc.dg/pr100464.c b/gcc/testsuite/gcc.dg/pr100464.c
new file mode 100644
index 00000000000..46cc37dff54
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr100464.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fcompare-debug" } */
+
+int *a;
+static int b, c, d, e, g, h;
+int f;
+void i() {
+  int *j[] = {&e, &b, &b, &d, &b, &b, &g, &e, &g, &b, &b,
+              &b, &b, &g, &e, &e, &b, &b, &d, &b, &b, &e,
+              &e, &g, &b, &b, &b, &b, &g, &e, &g, &c, &e};
+  int **k = &j[5];
+  for (; f;)
+    b |= *a;
+  *k = &h;
+}
+int main() {}
--
2.26.2