Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >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.
Unfortunately, pr78687.C is much more complicated and I can't explain
precisely what happens there. But it seems like a good idea to have
a way to avoid this optimization. So I've added the "noinline" check.
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/cpp2a/consteval-prop2.C: Adjust dg-bogus.
* g++.dg/tree-ssa/pr78687.C: Add __attribute__((noinline)).
* g++.dg/tree-ssa/pr90883.C: Likewise.
* g++.dg/cpp1y/constexpr-prvalue1.C: New test.
Co-authored-by: Patrick Palka <ppa...@redhat.com>
---
gcc/cp/cp-gimplify.cc | 14 +++++++++
gcc/testsuite/g++.dg/analyzer/pr97116.C | 2 +-
.../g++.dg/cpp1y/constexpr-prvalue1.C | 29 +++++++++++++++++++
gcc/testsuite/g++.dg/cpp2a/consteval-prop2.C | 2 +-
gcc/testsuite/g++.dg/tree-ssa/pr78687.C | 5 +++-
gcc/testsuite/g++.dg/tree-ssa/pr90883.C | 1 +
6 files changed, 50 insertions(+), 3 deletions(-)
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..41d6333f650 100644
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -1473,6 +1473,20 @@ 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))
{
+ tree fn;
+ if ((data->flags & ff_genericize)
+ /* Give the user an option to opt out. */
+ && !((fn = current_function_decl)
+ && lookup_attribute ("noinline",
+ DECL_ATTRIBUTES (fn))))
+ {
+ 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/cpp1y/constexpr-prvalue1.C
b/gcc/testsuite/g++.dg/cpp1y/constexpr-prvalue1.C
new file mode 100644
index 00000000000..45e3a382056
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-prvalue1.C
@@ -0,0 +1,29 @@
+// PR c++/116416
+// { dg-do compile { target c++14 } }
+
+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/cpp2a/consteval-prop2.C
b/gcc/testsuite/g++.dg/cpp2a/consteval-prop2.C
index 30129a4a266..64c06fb0b7d 100644
--- a/gcc/testsuite/g++.dg/cpp2a/consteval-prop2.C
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop2.C
@@ -68,7 +68,7 @@ test (int i)
{
int r = g (42) + g(i);
int t = k<int>(42)
- + k<int>(i); // { dg-bogus "call to|constant" "" { xfail *-*-* } }
+ + k<int>(i); // { dg-bogus "call to|constant" }
return r + t;
}
diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr78687.C
b/gcc/testsuite/g++.dg/tree-ssa/pr78687.C
index 698458f0e9a..7f5306bf841 100644
--- a/gcc/testsuite/g++.dg/tree-ssa/pr78687.C
+++ b/gcc/testsuite/g++.dg/tree-ssa/pr78687.C
@@ -446,7 +446,10 @@ struct qual_option
int quals_;
};
-inline ref_proxy<option_2, option_ref > make_object_1()
+// Compile-time evaluation of TARGET_EXPR's initials in cp_fold_r/TARGET_EXPR
+// breaks this test. The attribute prevents that early evaluation.
+__attribute__((noinline))
+ref_proxy<option_2, option_ref > make_object_1()
{
return ref_proxy<option_2, option_ref >(option_2());
}
diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr90883.C
b/gcc/testsuite/g++.dg/tree-ssa/pr90883.C
index 37df17d0b16..f66124945b6 100644
--- a/gcc/testsuite/g++.dg/tree-ssa/pr90883.C
+++ b/gcc/testsuite/g++.dg/tree-ssa/pr90883.C
@@ -7,6 +7,7 @@
int b{};
};
+ __attribute__((noinline))
C slow()
{
return {};
base-commit: 9227a64495d5594613604573b72422e8e3722fc5
--
2.46.0
