On Sat, Sep 28, 2024 at 08:39:12AM +0200, Jakub Jelinek wrote:
> On Fri, Sep 27, 2024 at 04:01:33PM +0200, Jakub Jelinek wrote:
> > So, I think we should go with (but so far completely untested except
> > for pr78687.C which is optimized with Marek's patch and the above testcase
> > which doesn't have the clearing anymore) the following patch.
> 
> That patch had a bug in type_has_padding_at_level_p and so it didn't
> bootstrap.
> 
> Here is a full patch which does.
[...]

And here's my patch, bootstrapped/regtested on x86_64-pc-linux-gnu
on top of Jakub's patch, ok for trunk once the prerequisite is in?

-- >8 --
This PR reports a missed optimization.  When we have:

  Str str{"Test"};
  callback(str);

as in the test, we're able to evaluate the Str::Str() call at compile
time.  But when we have:

  callback(Str{"Test"});

we are not.  With this patch (in fact, it's Patrick's patch with a little
tweak), we turn

  callback (TARGET_EXPR <D.2890, <<< Unknown tree: aggr_init_expr
    5
    __ct_comp
    D.2890
    (struct Str *) <<< Unknown tree: void_cst >>>
    (const char *) "Test" >>>>)

into

  callback (TARGET_EXPR <D.2890, {.str=(const char *) "Test", .length=4}>)

I explored the idea of calling maybe_constant_value for the whole
TARGET_EXPR in cp_fold.  That has three problems:
- we can't always elide a TARGET_EXPR, so we'd have to make sure the
  result is also a TARGET_EXPR;
- the resulting TARGET_EXPR must have the same flags, otherwise Bad
  Things happen;
- getting a new slot is also problematic.  I've seen a test where we
  had "TARGET_EXPR<D.2680, ...>, D.2680", and folding the whole TARGET_EXPR
  would get us "TARGET_EXPR<D.2681, ...>", but since we don't see the outer
  D.2680, we can't replace it with D.2681, and things break.

With this patch, two tree-ssa tests regressed: pr78687.C and pr90883.C.

FAIL: g++.dg/tree-ssa/pr90883.C   scan-tree-dump dse1 "Deleted redundant store: 
.*.a = {}"
is easy.  Previously, we would call C::C, so .gimple has:

  D.2590 = {};
  C::C (&D.2590);
  D.2597 = D.2590;
  return D.2597;

Then .einline inlines the C::C call:

  D.2590 = {};
  D.2590.a = {}; // #1
  D.2590.b = 0;  // #2
  D.2597 = D.2590;
  D.2590 ={v} {CLOBBER(eos)};
  return D.2597;

then #2 is removed in .fre1, and #1 is removed in .dse1.  So the test
passes.  But with the patch, .gimple won't have that C::C call, so the
IL is of course going to look different.  The .optimized dump looks the
same though so there's no problem.

pr78687.C was fixed by Jakub's categorize_ctor_elements_1 patch.

        PR c++/116416

gcc/cp/ChangeLog:

        * cp-gimplify.cc (cp_fold_r) <case TARGET_EXPR>: Try to fold
        TARGET_EXPR_INITIAL and replace it with the folded result if
        it's TREE_CONSTANT.

gcc/testsuite/ChangeLog:

        * g++.dg/analyzer/pr97116.C: Adjust dg-message.
        * g++.dg/tree-ssa/pr90883.C: Adjust dg-final.
        * g++.dg/cpp0x/constexpr-prvalue1.C: New test.
        * g++.dg/cpp1y/constexpr-prvalue1.C: New test.

Co-authored-by: Patrick Palka <ppa...@redhat.com>
---
 gcc/cp/cp-gimplify.cc                         | 10 +++++++
 gcc/testsuite/g++.dg/analyzer/pr97116.C       |  2 +-
 .../g++.dg/cpp0x/constexpr-prvalue1.C         | 24 +++++++++++++++
 .../g++.dg/cpp1y/constexpr-prvalue1.C         | 30 +++++++++++++++++++
 gcc/testsuite/g++.dg/tree-ssa/pr90883.C       |  4 +--
 5 files changed, 67 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-prvalue1.C
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-prvalue1.C

diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
index 003e68f1ea7..c63fdf3edd1 100644
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -1473,6 +1473,16 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)
         that case, strip it in favor of this one.  */
       if (tree &init = TARGET_EXPR_INITIAL (stmt))
        {
+         if ((data->flags & ff_genericize)
+             && !flag_no_inline)
+           {
+             tree folded = maybe_constant_init (init, TARGET_EXPR_SLOT (stmt));
+             if (folded != init && TREE_CONSTANT (folded))
+               {
+                 init = folded;
+                 break;
+               }
+           }
          cp_walk_tree (&init, cp_fold_r, data, NULL);
          cp_walk_tree (&TARGET_EXPR_CLEANUP (stmt), cp_fold_r, data, NULL);
          *walk_subtrees = 0;
diff --git a/gcc/testsuite/g++.dg/analyzer/pr97116.C 
b/gcc/testsuite/g++.dg/analyzer/pr97116.C
index d8e08a73172..1c404c2ceb2 100644
--- a/gcc/testsuite/g++.dg/analyzer/pr97116.C
+++ b/gcc/testsuite/g++.dg/analyzer/pr97116.C
@@ -16,7 +16,7 @@ struct foo
 void test_1 (void)
 {
   foo *p = new(NULL) foo (42); // { dg-warning "non-null expected" "warning" }
-  // { dg-message "argument 'this' \\(\[^\n\]*\\) NULL where non-null 
expected" "final event" { target *-*-* } .-1 }
+  // { dg-message "argument 'this'( \\(\[^\n\]*\\))? NULL where non-null 
expected" "final event" { target *-*-* } .-1 }
 }
 
 int test_2 (void)
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-prvalue1.C 
b/gcc/testsuite/g++.dg/cpp0x/constexpr-prvalue1.C
new file mode 100644
index 00000000000..f09088d41e8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-prvalue1.C
@@ -0,0 +1,24 @@
+// PR c++/116416
+// { dg-do compile { target c++11 } }
+// { dg-options "-O" }
+
+struct optional {
+  constexpr optional(int) {}
+};
+optional foo() { return 2; }
+
+
+struct C {
+  constexpr C(int) {}
+};
+
+struct B {
+  C fn(int) { return 0; }
+};
+
+void
+g ()
+{
+  B b;
+  b.fn(0);
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-prvalue1.C 
b/gcc/testsuite/g++.dg/cpp1y/constexpr-prvalue1.C
new file mode 100644
index 00000000000..ad31e300116
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-prvalue1.C
@@ -0,0 +1,30 @@
+// PR c++/116416
+// { dg-do compile { target c++14 } }
+// { dg-options "-O" }
+
+struct Str {
+  constexpr Str() {}
+  constexpr Str(const char *instr) {
+      str = instr; length = 0;
+      for (auto index = 0; instr[index]; ++index) {
+        ++length;
+      }
+  }
+  const char *str = nullptr;
+  int length = 0;
+};
+extern void callback(Str str);
+void
+func1()
+{
+    callback(Str{"Test"});
+}
+void
+func2()
+{
+    Str str{"Test"};
+    callback(str);
+}
+
+// Check that we don't call Str::Str(char const*)
+// { dg-final { scan-assembler-not "_ZN3StrC1EPKc" } }
diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr90883.C 
b/gcc/testsuite/g++.dg/tree-ssa/pr90883.C
index 37df17d0b16..ad9231eaff2 100644
--- a/gcc/testsuite/g++.dg/tree-ssa/pr90883.C
+++ b/gcc/testsuite/g++.dg/tree-ssa/pr90883.C
@@ -16,5 +16,5 @@
 // We want to match enough here to capture that we deleted an empty
 // constructor store
 // mips will expand to loop to clear because CLEAR_RATIO.
-// { dg-final { scan-tree-dump "Deleted redundant store: .*\.a = {}" "dse1" { 
xfail { mips*-*-* } } } }
-
+// { dg-final { scan-tree-dump-not ".*\.a = {}" "dse1" { xfail { mips*-*-* } } 
} }
+// { dg-final { scan-tree-dump-not ".*\.b = 0" "dse1" { xfail { mips*-*-* } } 
} }

base-commit: 1f619fe25925a5f79b9c33962e7a72e1f9fa4444
-- 
2.46.2

Reply via email to