MemBehavior: correctly handle debug_value

debug_value just "reads" the operand if it is an address.

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/TestPasses/MemBehaviorDumper.swift

@@ -71,7 +71,8 @@ private extension Instruction {
          is LoadInst,
          is StoreInst,
          is CopyAddrInst,
-         is BuiltinInst:
+         is BuiltinInst,
+         is DebugValueInst:
       return true
     default:
       return false

lib/SILOptimizer/Analysis/MemoryBehavior.cpp

@@ -176,6 +176,7 @@ class MemoryBehaviorVisitor
   MemBehavior visitDestroyValueInst(DestroyValueInst *DVI);
   MemBehavior visitSetDeallocatingInst(SetDeallocatingInst *BI);
   MemBehavior visitBeginCOWMutationInst(BeginCOWMutationInst *BCMI);
+  MemBehavior visitDebugValueInst(DebugValueInst *dv);
 #define ALWAYS_OR_SOMETIMES_LOADABLE_CHECKED_REF_STORAGE(Name, ...) \
   MemBehavior visit##Name##ReleaseInst(Name##ReleaseInst *BI);
 #include "swift/AST/ReferenceStorage.def"
@@ -374,6 +375,15 @@ visitBeginCOWMutationInst(BeginCOWMutationInst *BCMI) {
   return MemBehavior::None;
 }
 
+MemBehavior MemoryBehaviorVisitor::
+visitDebugValueInst(DebugValueInst *dv) {
+  SILValue op = dv->getOperand();
+  if (op->getType().isAddress() && mayAlias(op)) {
+    return MemBehavior::MayRead;
+  }
+  return MemBehavior::None;
+}
+
 //===----------------------------------------------------------------------===//
 //                            Top Level Entrypoint
 //===----------------------------------------------------------------------===//

test/SILOptimizer/mem-behavior.sil

@@ -1002,3 +1002,25 @@ bb0(%0 : $Builtin.RawPointer):
   %6 = tuple ()
   return %6 : $()
 }
+
+
+// CHECK-LABEL: @test_debug_value
+// CHECK:       PAIR #0.
+// CHECK-NEXT:      debug_value %0 : $*Int, let, name "x"
+// CHECK-NEXT:      %0 = alloc_stack $Int
+// CHECK-NEXT:    r=1,w=0
+// CHECK:       PAIR #1.
+// CHECK-NEXT:      debug_value %0 : $*Int, let, name "x"
+// CHECK-NEXT:      %1 = alloc_stack $Int
+// CHECK-NEXT:    r=0,w=0
+sil @test_debug_value : $@convention(thin) () -> () {
+bb0:
+  %0 = alloc_stack $Int
+  %1 = alloc_stack $Int
+  debug_value %0 : $*Int, let, name "x"
+  dealloc_stack %1 : $*Int
+  dealloc_stack %0 : $*Int
+  %r = tuple ()
+  return %r : $()
+}
+