https://gcc.gnu.org/g:12de1942a0a673f9f2f1c2bfce4279a666061ffc
commit r15-6052-g12de1942a0a673f9f2f1c2bfce4279a666061ffc
Author: Marek Polacek <pola...@redhat.com>
Date: Thu Aug 29 12:58:41 2024 -0400
c++: compile time evaluation of prvalues [PR116416]
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 is XFAILed because the test passes with r15-5746 but not with
r15-5747 as well. I opened <https://gcc.gnu.org/PR117971>.
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/pr78687.C: Add XFAIL.
* 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>
Reviewed-by: Jason Merrill <ja...@redhat.com>
Diff:
---
gcc/cp/cp-gimplify.cc | 10 +++++++--
gcc/testsuite/g++.dg/analyzer/pr97116.C | 2 +-
gcc/testsuite/g++.dg/cpp0x/constexpr-prvalue1.C | 24 ++++++++++++++++++++
gcc/testsuite/g++.dg/cpp1y/constexpr-prvalue1.C | 30 +++++++++++++++++++++++++
gcc/testsuite/g++.dg/tree-ssa/pr78687.C | 3 ++-
gcc/testsuite/g++.dg/tree-ssa/pr90883.C | 4 ++--
6 files changed, 67 insertions(+), 6 deletions(-)
diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
index b011badf00f4..623e2ee6e964 100644
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -1470,13 +1470,19 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void
*data_)
if (data->flags & ff_genericize)
cp_genericize_target_expr (stmt_p);
- /* Folding might replace e.g. a COND_EXPR with a TARGET_EXPR; in
- that case, strip it in favor of this one. */
if (tree &init = TARGET_EXPR_INITIAL (stmt))
{
cp_walk_tree (&init, cp_fold_r, data, NULL);
cp_walk_tree (&TARGET_EXPR_CLEANUP (stmt), cp_fold_r, data, NULL);
*walk_subtrees = 0;
+ if (!flag_no_inline)
+ {
+ tree folded = maybe_constant_init (init, TARGET_EXPR_SLOT (stmt));
+ if (folded != init && TREE_CONSTANT (folded))
+ init = folded;
+ }
+ /* Folding might replace e.g. a COND_EXPR with a TARGET_EXPR; in
+ that case, strip it in favor of this one. */
if (TREE_CODE (init) == TARGET_EXPR)
{
tree sub = TARGET_EXPR_INITIAL (init);
diff --git a/gcc/testsuite/g++.dg/analyzer/pr97116.C
b/gcc/testsuite/g++.dg/analyzer/pr97116.C
index d8e08a73172d..1c404c2ceb23 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 000000000000..f09088d41e80
--- /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 000000000000..ad31e3001167
--- /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/pr78687.C
b/gcc/testsuite/g++.dg/tree-ssa/pr78687.C
index 698458f0e9a5..6e8a5b7efdf9 100644
--- a/gcc/testsuite/g++.dg/tree-ssa/pr78687.C
+++ b/gcc/testsuite/g++.dg/tree-ssa/pr78687.C
@@ -480,4 +480,5 @@ int main(int argc, char* argv[])
f();
}
-/* { dg-final { scan-tree-dump "Removing load:.*ptr;" "sra" } } */
+// XFAILed due to PR116416
+/* { dg-final { scan-tree-dump "Removing load:.*ptr;" "sra" { xfail { *-*-* }
} } } */
diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr90883.C
b/gcc/testsuite/g++.dg/tree-ssa/pr90883.C
index 37df17d0b166..ad9231eaff24 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*-*-* } }
} }
