[flang-commits] [flang] 31786ee - [flang] Avoid undefined behaviour in Interval::Contains (#147505)

[via flang-commits]

Author: David Spickett
Date: 2025-07-08T14:39:08+01:00
New Revision: 31786ee89f683721248ef6c41d347a00a5e619f6

URL: https://github.com/llvm/llvm-project/commit/31786ee89f683721248ef6c41d347a00a5e619f6
DIFF: https://github.com/llvm/llvm-project/commit/31786ee89f683721248ef6c41d347a00a5e619f6.diff

LOG: [flang] Avoid undefined behaviour in Interval::Contains (#147505)

If the size of the other Interval was 0, (that.size_ - 1) would wrap
below zero.

I've fixed this so that a zero size interval A is within interval B if
the start of A is within B. There's a few ways you could handle zero
sized intervals in theory but this one passes all tests so I assume it's
the intention.

This fixes the following tests when ubsan is enabled:
  Flang :: Lower/OpenMP/PFT/sections-pft.f90
  Flang :: Lower/OpenMP/derived-type-allocatable.f90
  Flang :: Lower/OpenMP/privatization-proc-ptr.f90
  Flang :: Lower/OpenMP/sections.f90
  Flang :: Parser/OpenMP/sections.f90
  Flang :: Semantics/OpenMP/clause-validity01.f90
  Flang :: Semantics/OpenMP/if-clause.f90
  Flang :: Semantics/OpenMP/parallel-sections01.f90
  Flang :: Semantics/OpenMP/private-assoc.f90

Added: 
    

Modified: 
    flang/include/flang/Common/interval.h

Removed: 
    


################################################################################
diff  --git a/flang/include/flang/Common/interval.h b/flang/include/flang/Common/interval.h
index c4cab0ccf1130..2f0b6d9b55fe5 100644
--- a/flang/include/flang/Common/interval.h
+++ b/flang/include/flang/Common/interval.h
@@ -60,7 +60,8 @@ template <typename A> class Interval {
     return start_ <= x && x < start_ + size_;
   }
   constexpr bool Contains(const Interval &that) const {
-    return Contains(that.start_) && Contains(that.start_ + (that.size_ - 1));
+    return Contains(that.start_) &&
+        ((that.size_ == 0) || Contains(that.start_ + (that.size_ - 1)));
   }
   constexpr bool IsDisjointWith(const Interval &that) const {
     return that.NextAfter() <= start_ || NextAfter() <= that.start_;