[PATCH] c++: Fix compile-time-hog in cp_fold_immediate_r [PR111660]

[Marek Polacek <polacek@redhat.com>]

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;
     case PTRMEM_CST:
       if (TREE_CODE (PTRMEM_CST_MEMBER (stmt)) == FUNCTION_DECL
 	  && DECL_IMMEDIATE_FUNCTION_P (PTRMEM_CST_MEMBER (stmt)))
@@ -1145,7 +1145,8 @@ cp_fold_immediate (tree *tp, mce_value manifestly_const_eval)
     flags |= ff_mce_false;
 
   cp_fold_data data (flags);
-  return !!cp_walk_tree_without_duplicates (tp, cp_fold_immediate_r, &data);
+  tree r = cp_walk_tree_without_duplicates (tp, cp_fold_immediate_r, &data);
+  return r == error_mark_node;
 }
 
 /* Perform any pre-gimplification folding of C++ front end trees to
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() {}

base-commit: 8bd11fa4ffcf8bceb6511a9d6918c90a34b705b5
-- 
2.41.0