On 5/4/20 3:44 PM, Patrick Palka wrote:
When folding a CALL_EXPR, we can avoid copying it until folding changes
one of its arguments. And when folding a TREE_VEC, we can avoid using
an intermediate releasing_vec by working with a copy of the TREE_VEC as
soon as folding changes one of its arguments, like we do in the
CALL_EXPR case.
Incidentally, the CALL_EXPR change also fixes the testcase in PR94038.
The reason is that the call to maybe_constant_value from cp_fold on
bar<int>() now reuses the result of the earlier call to
maybe_constant_value from fold_for_warn, via the cv_cache. This earlier
call passes uid_sensitive=true, whereas the call from cp_fold passes
uid_sensitive=false, and so by reusing the earlier call we now avoid
instantiating bar<int> at all.
Passes 'make check-c++', does this look OK to commit to master after a
full bootstrap and regtest?
OK.
gcc/cp/ChangeLog:
PR c++/94038
* cp-gimplify.c (cp_fold) <case CALL_EXPR>: Move some variable
declarations closer to their uses. Copy the CALL_EXPR only
when one of its arguments has changed.
(cp_fold) <case TREE_VEC>: Instead of first collecting the
folded arguments into a releasing_vec, just make a copy of the
TREE_VEC as soon as folding changes one of its arguments.
gcc/testsuite/ChangeLog:
PR c++/94038
* g++.dg/warn/pr94038.C: New test.
---
gcc/cp/cp-gimplify.c | 39 ++++++++++++-----------------
gcc/testsuite/g++.dg/warn/pr94038.C | 26 +++++++++++++++++++
2 files changed, 42 insertions(+), 23 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/warn/pr94038.C
diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c
index f326d71637b..fc26a85f43a 100644
--- a/gcc/cp/cp-gimplify.c
+++ b/gcc/cp/cp-gimplify.c
@@ -2744,7 +2744,7 @@ cp_fold (tree x)
case CALL_EXPR:
{
- int i, m, sv = optimize, nw = sv, changed = 0;
+ int sv = optimize, nw = sv;
tree callee = get_callee_fndecl (x);
/* Some built-in function calls will be evaluated at compile-time in
@@ -2770,10 +2770,9 @@ cp_fold (tree x)
break;
}
- x = copy_node (x);
-
- m = call_expr_nargs (x);
- for (i = 0; i < m; i++)
+ bool changed = false;
+ int m = call_expr_nargs (x);
+ for (int i = 0; i < m; i++)
{
r = cp_fold (CALL_EXPR_ARG (x, i));
if (r != CALL_EXPR_ARG (x, i))
@@ -2783,9 +2782,11 @@ cp_fold (tree x)
x = error_mark_node;
break;
}
- changed = 1;
+ if (!changed)
+ x = copy_node (x);
+ CALL_EXPR_ARG (x, i) = r;
+ changed = true;
}
- CALL_EXPR_ARG (x, i) = r;
}
if (x == error_mark_node)
break;
@@ -2825,8 +2826,6 @@ cp_fold (tree x)
break;
}
- if (!changed)
- x = org_x;
break;
}
@@ -2865,24 +2864,18 @@ cp_fold (tree x)
case TREE_VEC:
{
bool changed = false;
- releasing_vec vec;
- int i, n = TREE_VEC_LENGTH (x);
- vec_safe_reserve (vec, n);
+ int n = TREE_VEC_LENGTH (x);
- for (i = 0; i < n; i++)
+ for (int i = 0; i < n; i++)
{
tree op = cp_fold (TREE_VEC_ELT (x, i));
- vec->quick_push (op);
if (op != TREE_VEC_ELT (x, i))
- changed = true;
- }
-
- if (changed)
- {
- r = copy_node (x);
- for (i = 0; i < n; i++)
- TREE_VEC_ELT (r, i) = (*vec)[i];
- x = r;
+ {
+ if (!changed)
+ x = copy_node (x);
+ TREE_VEC_ELT (x, i) = op;
+ changed = true;
+ }
}
}
diff --git a/gcc/testsuite/g++.dg/warn/pr94038.C b/gcc/testsuite/g++.dg/warn/pr94038.C
new file mode 100644
index 00000000000..4edfae72d99
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/pr94038.C
@@ -0,0 +1,26 @@
+// PR c++/94038
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-O -Wall" }
+
+template<typename T>
+constexpr int
+foo()
+{
+ static_assert(T(1) == 0, "");
+ return 0;
+}
+
+template<typename T>
+constexpr int
+bar()
+{
+ return foo<T>();
+}
+
+constexpr int
+baz(int a)
+{
+ return a;
+}
+
+static_assert(decltype(baz(bar<int>())){} == 0, "");
