[PATCH] cobol: Replace quadratic loop removing std::set elements

[Jonathan Wakely]

There's no need to keep using std::find_if from the beginning of the
container after every removal, just update the iterator after erasing an
element.

This is how C++20 std::erase_if is implemented.

gcc/cobol/ChangeLog:

        * except.cc (cbl_enabled_exceptions_t::turn_on_off): Replace
        quadratic loop with a single pass.
---

Tested x86_64-linux with make check-gcc-cobol.

 gcc/cobol/except.cc | 32 ++++++++++++++------------------
 1 file changed, 14 insertions(+), 18 deletions(-)

diff --git a/gcc/cobol/except.cc b/gcc/cobol/except.cc
index 5374201b4c8..43339627f1d 100644
--- a/gcc/cobol/except.cc
+++ b/gcc/cobol/except.cc
@@ -116,31 +116,27 @@ cbl_enabled_exceptions_t::turn_on_off( bool enabled,
     return true;
   }
 
-  /*
-   * std::remove_if cannot be used with std::set because its elements are 
const.
-   * std::set::erase_if became available only in C++20.
-   */
+  // std::set::erase_if became available only in C++20.
   if( enabled ) { // remove any disabled
     if( files.empty() ) {
       auto p = begin();
-      while( end() != (p = std::find_if( begin(), end(),
-                                         [ec = type]( const auto& elem ) {
-                                           return
-                                             !elem.enabled &&
-                                             ec_cmp(ec, elem.ec); } )) ) {
-        erase(p);
+      while( p != end() ) {
+       if( !p->enabled && ec_cmp(type, p->ec) ) {
+         p = erase(p);
+       } else {
+         ++p;
+       }
       }
     } else {
       for( size_t file: files ) {
         auto p = begin();
-        while( end() != (p = std::find_if( begin(), end(),
-                                           [ec = type, file]( const auto& elem 
) {
-                                             return
-                                               !elem.enabled &&
-                                               file == elem.file &&
-                                               ec_cmp(ec, elem.ec); } )) ) {
-          erase(p);
-        }
+        while( p != end() ) {
+         if( !p->enabled && file == p->file && ec_cmp(type, p->ec) ) {
+           p = erase(p);
+         } else {
+           ++p;
+         }
+       }
       }
     }
     auto elem = cbl_enabled_exception_t(enabled, location, type);
-- 
2.48.1