Don't put compiler generated objects in equivalence groups (#993)

Equivalence analysis has some problems that may be addressed by shifting
the core analysis to the front end.  Pending such changes, don't attempt
to place compiler generated objects in any equivalence group.

Author: vdonaldson

flang/lib/Lower/PFTBuilder.cpp

@@ -1449,8 +1449,11 @@ struct SymbolDependenceDepth {
 private:
   /// Skip symbol in alias analysis.
   bool skipSymbol(const semantics::Symbol &sym) {
+    // Common block equivalences are largely managed by the front end.
+    // Compiler generated symbols ('.' names) cannot be equivalenced.
+    // FIXME: Equivalence code generation may need to be revisited.
     return !sym.has<semantics::ObjectEntityDetails>() ||
-           lower::definedInCommonBlock(sym);
+           lower::definedInCommonBlock(sym) || sym.name()[0] == '.';
   }
 
   // Make sure the table is of appropriate size.

flang/test/Lower/equivalence-1.f90

@@ -31,3 +31,31 @@ SUBROUTINE s2
   ! CHECK: = fir.load %[[fld]] : !fir.ref<f32>
   PRINT *, r(3)
 END SUBROUTINE s2
+
+! CHECK-LABEL: func @_QPs3
+SUBROUTINE s3
+  REAL r(10)
+  TYPE t
+    SEQUENCE
+    REAL r(10)
+  END TYPE t
+  TYPE(t) x
+  ! CHECK: %[[group:.*]] = fir.alloca !fir.array<40xi8>
+  EQUIVALENCE (r,x)
+  ! CHECK: %[[coor:.*]] = fir.coordinate_of %[[group]], %c0 : (!fir.ref<!fir.array<40xi8>>, index) -> !fir.ref<i8>
+  ! CHECK: %[[rloc:.*]] = fir.convert %[[coor]] : (!fir.ref<i8>) -> !fir.ref<!fir.array<10xf32>>
+  ! CHECK: %[[xloc:.*]] = fir.convert %[[coor]] : (!fir.ref<i8>) -> !fir.ref<!fir.type<_QFs3Tt{r:!fir.array<10xf32>}>>
+  ! CHECK: %[[fidx:.*]] = fir.field_index r, !fir.type<_QFs3Tt{r:!fir.array<10xf32>}>
+  ! CHECK: %[[xrloc:.*]] = fir.coordinate_of %[[xloc]], %[[fidx]] :
+  ! CHECK: %[[v1loc:.*]] = fir.coordinate_of %[[xrloc]], %c8_i64 : (!fir.ref<!fir.array<10xf32>>, i64) -> !fir.ref<f32>
+  ! CHECK: fir.store %{{.*}} to %[[v1loc]] : !fir.ref<f32>
+  x%r(9) = 9.0
+  ! CHECK: %[[v2loc:.*]] = fir.coordinate_of %[[rloc]], %c8_i64 : (!fir.ref<!fir.array<10xf32>>, i64) -> !fir.ref<f32>
+  ! CHECK: %{{.*}} = fir.load %[[v2loc]] : !fir.ref<f32>
+  PRINT *, r(9)
+END SUBROUTINE s3
+
+  CALL s1
+  CALL s2
+  CALL s3
+END