Rebased to commit 83f065d

Author: Renaud-K

flang/include/flang/Optimizer/Analysis/AliasAnalysis.h

@@ -64,6 +64,7 @@ struct AliasAnalysis {
   //  subroutine test()
   //    use top
   //    a(1) = 1
+  //  end subroutine
   //  -------------------------------------------------
   // 
   //  flang-new -fc1 -emit-fir test.f90 -o test.fir

flang/lib/Optimizer/Analysis/AliasAnalysis.cpp

@@ -108,7 +108,7 @@ AliasResult AliasAnalysis::alias(Value lhs, Value rhs) {
   auto lhsSrc = getSource(lhs);
   auto rhsSrc = getSource(rhs);
   bool approximateSource = lhsSrc.approximateSource || rhsSrc.approximateSource;
-  LLVM_DEBUG(llvm::dbgs() << "\n"; llvm::dbgs() << "AliasAnalysis::alias\n";
+  LLVM_DEBUG(llvm::dbgs() << "\nAliasAnalysis::alias\n";
              llvm::dbgs() << "  lhs: " << lhs << "\n";
              llvm::dbgs() << "  lhsSrc: " << lhsSrc << "\n";
              llvm::dbgs() << "  rhs: " << rhs << "\n";
@@ -173,8 +173,9 @@ AliasResult AliasAnalysis::alias(Value lhs, Value rhs) {
     return AliasResult::MayAlias;
   }
 
-  // POINTER components may alias with POINTER objects,
-  // as well as other POINTER components
+  // Box for POINTER component inside an object of a derived type
+  // may alias box of a POINTER object, as well as boxes for POINTER
+  // components inside two objects of derived types may alias.
   if ((src1->isRecordWithPointerComponent() && src2->isTargetOrPointer()) ||
       (src2->isRecordWithPointerComponent() && src1->isTargetOrPointer()) ||
       (src1->isRecordWithPointerComponent() &&

flang/test/Analysis/AliasAnalysis/alias-analysis-9.fir

@@ -21,11 +21,13 @@
 // CHECK-DAG: x#0 <-> y#0: MayAlias
 
 // TODO: y is not a pointer object and therefore does not alias with the x%next component. 
+//       Also assigning x to y would not modify x.next
 // CHECK-DAG: y#0 <-> xnext1#0: MayAlias
 // CHECK-DAG: y#0 <-> xnext2#0: MayAlias
 
-// Pointer components may alias with pointer objects, 
-// as well as other pointer components
+// We need to catch the fact that assigning y to x will modify xnext. 
+// The only side-effect between the 2 loads of x.next is the assignment to x, 
+// therefore x needs to alias with x.next to prevent the loads from being merged.
 // CHECK-DAG: x#0 <-> xnext1#0: MayAlias
 // CHECK-DAG: x#0 <-> xnext2#0: MayAlias