[PATCH] D84281: [flang] Replay a FORMAT at the right position

[Peter Klausler via Phabricator via llvm-commits]

klausler created this revision.
klausler added reviewers: sscalpone, PeteSteinfeld, schweitz.
klausler added a project: Flang.
Herald added a reviewer: jdoerfert.
Herald added a reviewer: DavidTruby.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

When FORMAT control reaches the final parenthesis and data items
remain, we advance a record and revert to the beginning of the
FORMAT for further items.  But when the FORMAT contains any
nested parenthesized group of editing descriptors, possibly
repeated, reversion must be to the beginning of the last such
top-level parenthesized group, including its repetition count.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D84281

Files:
  flang/runtime/format-implementation.h


Index: flang/runtime/format-implementation.h
===================================================================
--- flang/runtime/format-implementation.h
+++ flang/runtime/format-implementation.h
@@ -225,6 +225,7 @@
   while (true) {
     std::optional<int> repeat;
     bool unlimited{false};
+    auto maybeReversionPoint{offset_};
     CharType ch{GetNextChar(context)};
     while (ch == ',' || ch == ':') {
       // Skip commas, and don't complain if they're missing; the format
@@ -254,6 +255,7 @@
         return 0;
       }
       stack_[height_].start = offset_ - 1; // the '('
+      RUNTIME_CHECK(context, format_[stack_[height_].start] == '(');
       if (unlimited || height_ == 0) {
         stack_[height_].remaining = Iteration::unlimited;
         unlimitedLoopCheck = offset_ - 1;
@@ -265,6 +267,12 @@
       } else {
         stack_[height_].remaining = 0;
       }
+      if (height_ == 1) {
+        // Subtle point (F'2018 13.4 para 9): tha last parenthesized group
+        // at height 1 becomes the restart point after control reaches the
+        // end of the format, including its repeat count.
+        stack_[0].start = maybeReversionPoint - 1;
+      }
       ++height_;
     } else if (height_ == 0) {
       context.SignalError(IostatErrorInFormat, "FORMAT lacks initial '('");
@@ -276,14 +284,15 @@
         }
         context.AdvanceRecord(); // implied / before rightmost )
       }
+      auto restart{stack_[height_ - 1].start + 1};
       if (stack_[height_ - 1].remaining == Iteration::unlimited) {
-        offset_ = stack_[height_ - 1].start + 1;
+        offset_ = restart;
         if (offset_ == unlimitedLoopCheck) {
           context.SignalError(IostatErrorInFormat,
               "Unlimited repetition in FORMAT lacks data edit descriptors");
         }
       } else if (stack_[height_ - 1].remaining-- > 0) {
-        offset_ = stack_[height_ - 1].start + 1;
+        offset_ = restart;
       } else {
         --height_;
       }
@@ -396,7 +405,7 @@
     ++height_;
   }
   edit.repeat = 1;
-  if (height_ > 1) {
+  if (height_ > 1) { // Subtle: stack_[0].start doesn't necessarily point to '('
     int start{stack_[height_ - 1].start};
     if (format_[start] != '(') {
       if (stack_[height_ - 1].remaining > maxRepeat) {


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