EscapeAnalysis: fix a wrong use-point detection.

This caused redundant load elimination to remove a load although the value is overwritten in a called function.
Most likely this could only occur if the load address is a block argument.

fixes SR-4393

Author: eeckstein

lib/SILOptimizer/Analysis/EscapeAnalysis.cpp

@@ -1818,9 +1818,16 @@ bool EscapeAnalysis::canObjectOrContentEscapeTo(SILValue V, FullApplySite FAS) {
   if (ConGraph->isUsePoint(UsePoint, Node))
     return true;
 
-  if (hasReferenceSemantics(V->getType())) {
-    // Check if the object "content", i.e. a pointer to one of its stored
-    // properties, can escape to the called function.
+  if (isPointer(V)) {
+    // Check if the object "content" can escape to the called function.
+    // This will catch cases where V is a reference and a pointer to a stored
+    // property escapes.
+    // It's also important in case of a pointer assignment, e.g.
+    //    V = V1
+    //    apply(V1)
+    // In this case the apply is only a use-point for V1 and V1's content node.
+    // As V1's content node is the same as V's content node, we also make the
+    // check for the content node.
     CGNode *ContentNode = ConGraph->getContentNode(Node);
     if (ContentNode->escapesInsideFunction(false))
       return true;

test/SILOptimizer/redundant_load_elim.sil

@@ -1166,3 +1166,27 @@ bb0(%0 : $Builtin.RawPointer):
   return %6 : $Int
 }
 
+sil @overwrite_int : $@convention(thin) (@inout Int, Int) -> ()
+
+// CHECK-LABEL: sil @test_address_block_args
+// CHECK: bb2({{.*}}):
+// CHECK: apply
+// CHECK: [[L:%.*]] = load
+// CHECK: return [[L]]
+sil @test_address_block_args : $@convention(thin) (Int) -> Int {
+bb0(%0 : $Int):
+  %4 = alloc_stack $Int
+  store %0 to %4 : $*Int
+  cond_br undef, bb1(%4 : $*Int), bb2(%4 : $*Int)
+
+bb1(%a1 : $*Int):
+  br bb2(%a1 : $*Int)
+
+bb2(%a : $*Int):
+  %l1 = load %a : $*Int
+  %60 = function_ref @overwrite_int : $@convention(thin) (@inout Int, Int) -> ()
+  %61 = apply %60(%4, %l1) : $@convention(thin) (@inout Int, Int) -> ()
+  %r = load %a : $*Int
+  dealloc_stack %4 : $*Int
+  return %r : $Int
+}