[flang] Fix vector cshift runtime with non zero lower bounds

[jeanPerier]

Summary

The source index should not be compared to zero after applying the
shift with the modulo, it must be compared to the lower bound.
Otherwise, the extent is not added in case it should and the computed
source index may be less than the lower bound, causing invalid results.

[klausler]

Can you please also take a quick look at EOSHIFT and check my similar logic there?

[jeanPerier]

Can you please also take a quick look at EOSHIFT and check my similar logic there?

Sure. The code looks OK, but I will check this with a test and add this here.

[jeanPerier]

Add an test with non zero lower bound for EOSHIFT too (the code was OK).

flang/runtime/transformational.cpp

void RTNAME(CshiftVector)(Descriptor &result, const Descriptor &source,
   RUNTIME_CHECK(terminator, source.rank() == 1);
   const Dimension &sourceDim{source.GetDimension(0)};
   SubscriptValue extent{sourceDim.Extent()};
   AllocateResult(result, source, 1, &extent, terminator, "CSHIFT");
   SubscriptValue lb{sourceDim.LowerBound()};
   for (SubscriptValue j{0}; j < extent; ++j) {
     SubscriptValue resultAt{1 + j};
     SubscriptValue sourceAt{lb + (j + shift) % extent};
-    if (sourceAt < 0) {
+    if (sourceAt < lb) {
       sourceAt += extent;
     }
     CopyElement(result, &resultAt, source, &sourceAt, terminator);
   }
 }
 
 // EOSHIFT of rank > 1
 void RTNAME(Eoshift)(Descriptor &result, const Descriptor &source,

flang/unittests/Runtime/Transformational.cpp

TEST(Transformational, Shifts) {
   EXPECT_EQ(vectorResult.type(), (TypeCode{TypeCategory::Integer, 4}));
   static std::int32_t cshiftExpect4[6]{5, 6, 1, 2, 3, 4};
   for (int j{0}; j < 6; ++j) {
     EXPECT_EQ(*vectorResult.ZeroBasedIndexedElement<std::int32_t>(j),
         cshiftExpect4[j]);
   }
   vectorResult.Destroy();
 
+  // VECTOR  1 3 5 2 4 6 WITH non zero lower bound in a negative cshift.
+  auto vectorWithLowerBounds{MakeArray<TypeCategory::Integer, 4>(
+      std::vector<int>{6}, std::vector<std::int32_t>{1, 2, 3, 4, 5, 6})};
+  vector->GetDimension(0).SetLowerBound(2);
+  StaticDescriptor<1, true> vectorDesc2;
+
+  RTNAME(CshiftVector)
+  (vectorResult, *vectorWithLowerBounds, -2, __FILE__, __LINE__);
+  EXPECT_EQ(vectorResult.type(), array->type());
+  EXPECT_EQ(vectorResult.rank(), 1);
+  EXPECT_EQ(vectorResult.GetDimension(0).LowerBound(), 1);
+  EXPECT_EQ(vectorResult.GetDimension(0).Extent(), 6);
+  EXPECT_EQ(vectorResult.type(), (TypeCode{TypeCategory::Integer, 4}));
+  static std::int32_t cshiftExpect5[6]{5, 6, 1, 2, 3, 4};
+  for (int j{0}; j < 6; ++j) {
+    EXPECT_EQ(*vectorResult.ZeroBasedIndexedElement<std::int32_t>(j),
+        cshiftExpect5[j]);
+  }
+  vectorResult.Destroy();
+
   auto boundary{MakeArray<TypeCategory::Integer, 4>(
       std::vector<int>{3}, std::vector<std::int32_t>{-1, -2, -3})};
   boundary->GetDimension(0).SetLowerBound(9); // shouldn't matter
   RTNAME(Eoshift)(result, *array, *shift3, &*boundary, 1, __FILE__, __LINE__);
   EXPECT_EQ(result.type(), array->type());
   EXPECT_EQ(result.rank(), 2);
   EXPECT_EQ(result.GetDimension(0).LowerBound(), 1);
   EXPECT_EQ(result.GetDimension(0).Extent(), 2);
TEST(Transformational, Shifts) {
   EXPECT_EQ(vectorResult.GetDimension(0).Extent(), 6);
   EXPECT_EQ(vectorResult.type(), (TypeCode{TypeCategory::Integer, 4}));
   static std::int32_t eoshiftVectorExpect[6]{3, 4, 5, 6, 343, 343};
   for (int j{0}; j < 6; ++j) {
     EXPECT_EQ(*vectorResult.ZeroBasedIndexedElement<std::int32_t>(j),
         eoshiftVectorExpect[j]);
   }
   vectorResult.Destroy();
+
+  // VECTOR EOSHIFT on input with non zero lower bounds
+  RTNAME(EoshiftVector)
+  (vectorResult, *vectorWithLowerBounds, -2, &vectorBoundary, __FILE__,
+      __LINE__);
+  EXPECT_EQ(vectorResult.type(), array->type());
+  EXPECT_EQ(vectorResult.rank(), 1);
+  EXPECT_EQ(vectorResult.GetDimension(0).LowerBound(), 1);
+  EXPECT_EQ(vectorResult.GetDimension(0).Extent(), 6);
+  EXPECT_EQ(vectorResult.type(), (TypeCode{TypeCategory::Integer, 4}));
+  static std::int32_t eoshiftVectorExpect2[6]{343, 343, 1, 2, 3, 4};
+  for (int j{0}; j < 6; ++j) {
+    EXPECT_EQ(*vectorResult.ZeroBasedIndexedElement<std::int32_t>(j),
+        eoshiftVectorExpect2[j]);
+  }
+  vectorResult.Destroy();
 }
 
 TEST(Transformational, Pack) {
   // ARRAY  1 3 5
   //        2 4 6
   auto array{MakeArray<TypeCategory::Integer, 4>(
       std::vector<int>{2, 3}, std::vector<std::int32_t>{1, 2, 3, 4, 5, 6})};
   array->GetDimension(0).SetLowerBound(2); // shouldn't matter