On Thu, Oct 12, 2023 at 09:41:43PM -0400, Jason Merrill wrote:
On 10/12/23 17:04, Marek Polacek wrote:
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
My recent patch introducing cp_fold_immediate_r caused exponential
compile time with nested COND_EXPRs. The problem is that the COND_EXPR
case recursively walks the arms of a COND_EXPR, but after processing
both arms it doesn't end the walk; it proceeds to walk the
sub-expressions of the outermost COND_EXPR, triggering again walking
the arms of the nested COND_EXPR, and so on. This patch brings the
compile time down to about 0m0.033s.
I've added some debug prints to make sure that the rest of cp_fold_r
is still performed as before.
PR c++/111660
gcc/cp/ChangeLog:
* cp-gimplify.cc (cp_fold_immediate_r) <case COND_EXPR>: Return
integer_zero_node instead of break;.
(cp_fold_immediate): Return true if cp_fold_immediate_r returned
error_mark_node.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/hog1.C: New test.
---
gcc/cp/cp-gimplify.cc | 9 ++--
gcc/testsuite/g++.dg/cpp0x/hog1.C | 77 +++++++++++++++++++++++++++++++
2 files changed, 82 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/hog1.C
diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
index bdf6e5f98ff..ca622ca169a 100644
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -1063,16 +1063,16 @@ cp_fold_immediate_r (tree *stmt_p, int *walk_subtrees,
void *data_)
break;
if (TREE_OPERAND (stmt, 1)
&& cp_walk_tree (&TREE_OPERAND (stmt, 1), cp_fold_immediate_r, data,
- nullptr))
+ nullptr) == error_mark_node)
return error_mark_node;
if (TREE_OPERAND (stmt, 2)
&& cp_walk_tree (&TREE_OPERAND (stmt, 2), cp_fold_immediate_r, data,
- nullptr))
+ nullptr) == error_mark_node)
return error_mark_node;
/* We're done here. Don't clear *walk_subtrees here though: we're
called
from cp_fold_r and we must let it recurse on the expression with
cp_fold. */
- break;
+ return integer_zero_node;
I'm concerned this will end up missing something like
1 ? 1 : ((1 ? 1 : 1), immediate())
as the integer_zero_node from the inner ?: will prevent walk_tree from
looking any farther.
You are right. The line above works as expected, but
1 ? 1 : ((1 ? 1 : id (42)), id (i));
shows the problem (when the expression isn't used as an initializer).
Maybe we want to handle COND_EXPR in cp_fold_r instead of here?
I hope this version is better.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
My recent patch introducing cp_fold_immediate_r caused exponential
compile time with nested COND_EXPRs. The problem is that the COND_EXPR
case recursively walks the arms of a COND_EXPR, but after processing
both arms it doesn't end the walk; it proceeds to walk the
sub-expressions of the outermost COND_EXPR, triggering again walking
the arms of the nested COND_EXPR, and so on. This patch brings the
compile time down to about 0m0.033s.
The ff_fold_immediate flag is unused after this patch but since I'm
using it in the P2564 patch, I'm not removing it now.
PR c++/111660
gcc/cp/ChangeLog:
* cp-gimplify.cc (cp_fold_immediate_r) <case COND_EXPR>: Don't
handle it here.
(cp_fold_r): Handle COND_EXPR here.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/hog1.C: New test.
* g++.dg/cpp2a/consteval36.C: New test.
---
gcc/cp/cp-gimplify.cc | 38 +++++-------
gcc/testsuite/g++.dg/cpp0x/hog1.C | 77 ++++++++++++++++++++++++
gcc/testsuite/g++.dg/cpp2a/consteval36.C | 18 ++++++
3 files changed, 111 insertions(+), 22 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/hog1.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval36.C
diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
index bdf6e5f98ff..801cba141cb 100644
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -1052,27 +1052,6 @@ cp_fold_immediate_r (tree *stmt_p, int *walk_subtrees,
void *data_)
switch (TREE_CODE (stmt))
{
- /* Unfortunately we must handle code like
- false ? bar () : 42
- where we have to check bar too. The cp_fold call in cp_fold_r could
- fold the ?: into a constant before we see it here. */
- case COND_EXPR:
- /* If we are called from cp_fold_immediate, we don't need to worry about
- cp_fold folding away the COND_EXPR. */
- if (data->flags & ff_fold_immediate)
- break;
- if (TREE_OPERAND (stmt, 1)
- && cp_walk_tree (&TREE_OPERAND (stmt, 1), cp_fold_immediate_r, data,
- nullptr))
- return error_mark_node;
- if (TREE_OPERAND (stmt, 2)
- && cp_walk_tree (&TREE_OPERAND (stmt, 2), cp_fold_immediate_r, data,
- nullptr))
- return error_mark_node;
- /* We're done here. Don't clear *walk_subtrees here though: we're called
- from cp_fold_r and we must let it recurse on the expression with
- cp_fold. */
- break;
case PTRMEM_CST:
if (TREE_CODE (PTRMEM_CST_MEMBER (stmt)) == FUNCTION_DECL
&& DECL_IMMEDIATE_FUNCTION_P (PTRMEM_CST_MEMBER (stmt)))
@@ -1163,7 +1142,22 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)
enum tree_code code = TREE_CODE (stmt);
if (cxx_dialect > cxx17)
- cp_fold_immediate_r (stmt_p, walk_subtrees, data);
+ {
+ /* Unfortunately we must handle code like
+ false ? bar () : 42
+ where we have to check bar too. The cp_fold call below could
+ fold the ?: into a constant before we've checked it. */
+ if (code == COND_EXPR)
+ {
+ if (TREE_OPERAND (stmt, 1))
+ cp_walk_tree (&TREE_OPERAND (stmt, 1), cp_fold_immediate_r, data,
+ nullptr);
+ if (TREE_OPERAND (stmt, 2))
+ cp_walk_tree (&TREE_OPERAND (stmt, 2), cp_fold_immediate_r, data,
+ nullptr);
+ }
+ cp_fold_immediate_r (stmt_p, walk_subtrees, data);
+ }
*stmt_p = stmt = cp_fold (*stmt_p, data->flags);
diff --git a/gcc/testsuite/g++.dg/cpp0x/hog1.C b/gcc/testsuite/g++.dg/cpp0x/hog1.C
new file mode 100644
index 00000000000..105a2e912c4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/hog1.C
@@ -0,0 +1,77 @@
+// PR c++/111660
+// { dg-do compile { target c++11 } }
+
+enum Value {
+ LPAREN,
+ RPAREN,
+ LBRACE,
+ RBRACE,
+ LBRACK,
+ RBRACK,
+ CONDITIONAL,
+ COLON,
+ SEMICOLON,
+ COMMA,
+ PERIOD,
+ BIT_OR,
+ BIT_AND,
+ BIT_XOR,
+ BIT_NOT,
+ NOT,
+ LT,
+ GT,
+ MOD,
+ ASSIGN,
+ ADD,
+ SUB,
+ MUL,
+ DIV,
+ PRIVATE_NAME,
+ STRING,
+ TEMPLATE_SPAN,
+ IDENTIFIER,
+ WHITESPACE,
+ ILLEGAL,
+};
+
+constexpr Value GetOneCharToken(char c) {
+ return
+ c == '(' ? LPAREN :
+ c == ')' ? RPAREN :
+ c == '{' ? LBRACE :
+ c == '}' ? RBRACE :
+ c == '[' ? LBRACK :
+ c == ']' ? RBRACK :
+ c == '?' ? CONDITIONAL :
+ c == ':' ? COLON :
+ c == ';' ? SEMICOLON :
+ c == ',' ? COMMA :
+ c == '.' ? PERIOD :
+ c == '|' ? BIT_OR :
+ c == '&' ? BIT_AND :
+ c == '^' ? BIT_XOR :
+ c == '~' ? BIT_NOT :
+ c == '!' ? NOT :
+ c == '<' ? LT :
+ c == '>' ? GT :
+ c == '%' ? MOD :
+ c == '=' ? ASSIGN :
+ c == '+' ? ADD :
+ c == '-' ? SUB :
+ c == '*' ? MUL :
+ c == '/' ? DIV :
+ c == '#' ? PRIVATE_NAME :
+ c == '"' ? STRING :
+ c == '\'' ? STRING :
+ c == '`' ? TEMPLATE_SPAN :
+ c == '\\' ? IDENTIFIER :
+ c == ' ' ? WHITESPACE :
+ c == '\t' ? WHITESPACE :
+ c == '\v' ? WHITESPACE :
+ c == '\f' ? WHITESPACE :
+ c == '\r' ? WHITESPACE :
+ c == '\n' ? WHITESPACE :
+ ILLEGAL;
+}
+
+int main() {}
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval36.C
b/gcc/testsuite/g++.dg/cpp2a/consteval36.C
new file mode 100644
index 00000000000..d6aea214d61
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval36.C
@@ -0,0 +1,18 @@
+// PR c++/111660
+// { dg-do compile { target c++20 } }
+
+consteval int id (int i) { return i; }
+
+void
+g (int i)
+{
+ 1 ? 1 : ((1 ? 1 : 1), id (i)); // { dg-error "'i' is not a constant
expression" }
+ 1 ? 1 : ((1 ? 1 : 1), id (i), 1); // { dg-error "'i' is not a constant
expression" }
+ 1 ? 1 : ((i ? 1 : 1), id (i), 1); // { dg-error "'i' is not a constant
expression" }
+ 1 ? 1 : ((1 ? i : 1), id (i), 1); // { dg-error "'i' is not a constant
expression" }
+ 1 ? 1 : ((1 ? 1 : i), id (i), 1); // { dg-error "'i' is not a constant
expression" }
+ 1 ? 1 : ((i ? -i : i), id (i), 1); // { dg-error "'i' is not a constant
expression" }
+ 1 ? 1 : ((1 ? 1 : id (i)), id (42), 1); // { dg-error "'i' is not a constant
expression" }
+ 1 ? 1 : ((1 ? 1 : id (42)), id (i)); // { dg-error "'i' is not a constant
expression" }
+ 1 ? 1 : ((1 ? 1 : id (42)), id (i), 1); // { dg-error "'i' is not a constant
expression" }
+}
base-commit: 8be20f3b0bded7f9b690b27cbee58b283dbe827b
