[flang-commits] [PATCH] D121124: [flang] Avoid crash case in provenance mapping

[Peter Klausler via Phabricator via flang-commits]

klausler created this revision.
klausler added a reviewer: mleair.
klausler added a project: Flang.
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When a contiguous range of a cooked character stream is being
mapped to a range of source provenance, the code was assuming
that the "end()" position of the input range -- being the character
immediately after the range -- would also follow the range's
source provenance.  This isn't always the case.

Modify the code to work with the true last character of the
input range (at end()-1) and to also cope with cases when that
last position truly maps to an earlier provenance, which can happen
when the prescanner has inserted a space into the cooked character
stream.


https://reviews.llvm.org/D121124

Files:
  flang/lib/Parser/provenance.cpp


Index: flang/lib/Parser/provenance.cpp
===================================================================
--- flang/lib/Parser/provenance.cpp
+++ flang/lib/Parser/provenance.cpp
@@ -435,11 +435,15 @@
     return std::nullopt;
   }
   ProvenanceRange first{provenanceMap_.Map(cookedRange.begin() - &data_[0])};
-  if (cookedRange.size() <= first.size()) {
+  if (cookedRange.size() <= first.size()) { // always true when empty
     return first.Prefix(cookedRange.size());
   }
-  ProvenanceRange last{provenanceMap_.Map(cookedRange.end() - &data_[0])};
-  return {ProvenanceRange{first.start(), last.start() - first.start()}};
+  ProvenanceRange last{provenanceMap_.Map(cookedRange.end() - 1 - &data_[0])};
+  if (first.start() <= last.start()) {
+    return {ProvenanceRange{first.start(), last.start() - first.start() + 1}};
+  } else {
+    return std::nullopt;
+  }
 }
 
 std::optional<CharBlock> CookedSource::GetCharBlock(


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