Re: [PATCH] c++: non-dependent assignment checking [PR63198, PR18474]

[Jason Merrill via Gcc-patches]

On 9/17/23 14:51, Patrick Palka wrote:

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?  Patch generatde with -w to avoid noisy whitespace changes.

-- >8 --

This patch makes us recognize and check non-dependent simple assigments
ahead of time, like we already do for compound assignments.  This means
the templated representation of such assignments will now usually have
an implicit INDIRECT_REF (due to the reference return type), which the
-Wparentheses code needs to handle.  As a drive-by improvement, this
patch also makes maybe_convert_cond issue -Wparentheses warnings ahead
of time.

This revealed some libstdc++ tests were attempting to modify a data
member from a uninstantiated const member function; naively fixed by
making the data member mutable.

        PR c++/63198
        PR c++/18474

gcc/cp/ChangeLog:

        * semantics.cc (maybe_convert_cond): Look through implicit
        INDIRECT_REF when deciding whether to issue a -Wparentheses
        warning, and consider templated assignment expressions as well.
        (finish_parenthesized_expr): Look through implicit INDIRECT_REF
        when suppressing -Wparentheses warning.
        * typeck.cc (build_x_modify_expr): Check simple assignments
        ahead time too, not just compound assignments.  Give the second
        operand of MODOP_EXPR a non-null type so that it's not considered
        always instantiation-dependent.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp0x/static_assert15.C: Expect diagnostic for
        non-constant static_assert condition.
        * g++.dg/expr/unary2.C: Remove xfails.
        * g++.dg/template/init7.C: Make initializer type-dependent to
        preserve intent of test.
        * g++.dg/template/recurse3.C: Likewise for the erroneous
        statement.
        * g++.dg/template/non-dependent26.C: New test.
        * g++.dg/warn/Wparentheses-32.C: New test.

libstdc++/ChangeLog:

        * testsuite/26_numerics/random/discard_block_engine/cons/seed_seq2.cc:
        Make seed_seq::called member mutable.
        * 
testsuite/26_numerics/random/independent_bits_engine/cons/seed_seq2.cc:
        Likewise.
        * 
testsuite/26_numerics/random/linear_congruential_engine/cons/seed_seq2.cc
        Likewise.
        * 
testsuite/26_numerics/random/mersenne_twister_engine/cons/seed_seq2.cc:
        Likewise.
        * testsuite/26_numerics/random/shuffle_order_engine/cons/seed_seq2.cc:
        Likewise.
        * 
testsuite/26_numerics/random/subtract_with_carry_engine/cons/seed_seq2.cc:
        Likewise.
        * 
testsuite/ext/random/simd_fast_mersenne_twister_engine/cons/seed_seq2.cc
        Likewise.
---
  gcc/cp/semantics.cc                           | 17 +++++++----
  gcc/cp/typeck.cc                              | 23 +++++++--------
  gcc/testsuite/g++.dg/cpp0x/static_assert15.C  |  2 +-
  gcc/testsuite/g++.dg/expr/unary2.C            |  8 ++----
  gcc/testsuite/g++.dg/template/init7.C         |  2 +-
  .../g++.dg/template/non-dependent26.C         | 25 +++++++++++++++++
  gcc/testsuite/g++.dg/template/recurse3.C      |  8 +++---
  gcc/testsuite/g++.dg/warn/Wparentheses-32.C   | 28 +++++++++++++++++++
  .../discard_block_engine/cons/seed_seq2.cc    |  2 +-
  .../independent_bits_engine/cons/seed_seq2.cc |  2 +-
  .../cons/seed_seq2.cc                         |  2 +-
  .../mersenne_twister_engine/cons/seed_seq2.cc |  2 +-
  .../shuffle_order_engine/cons/seed_seq2.cc    |  2 +-
  .../cons/seed_seq2.cc                         |  2 +-
  .../cons/seed_seq2.cc                         |  2 +-
  15 files changed, 91 insertions(+), 36 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/template/non-dependent26.C
  create mode 100644 gcc/testsuite/g++.dg/warn/Wparentheses-32.C

diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 0f7f4e87ae4..b57c1ac868b 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 459739d5866..74f5fced060 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -9739,15 +9739,15 @@ build_x_modify_expr (location_t loc, tree lhs, enum 
tree_code modifycode,
        rhs = build_non_dependent_expr (rhs);
      }

- if (modifycode != NOP_EXPR)

-    {
-      tree op = build_nt (modifycode, NULL_TREE, NULL_TREE);
-      tree rval = build_new_op (loc, MODIFY_EXPR, LOOKUP_NORMAL,
+  tree rval;
+  if (modifycode == NOP_EXPR)
+    rval = cp_build_modify_expr (loc, lhs, modifycode, rhs, complain);
+  else
+    rval = build_new_op (loc, MODIFY_EXPR, LOOKUP_NORMAL,
                         lhs, rhs, op, lookups, &overload, complain);
-      if (rval)
-       {
    if (rval == error_mark_node)
-           return rval;
+    return error_mark_node;
+  if (modifycode != NOP_EXPR)
      suppress_warning (rval /* What warning? */);

Did you try disabling this to see if it's still needed?

Jason