Enable run-time exclusivity checking in release mode.

This change could impact Swift programs that previously appeared
well-behaved, but weren't fully tested in debug mode. Now, when running
in release mode, they may trap with the message "error: overlapping
accesses...".

Recent optimizations have brought performance where I think it needs
to be for adoption. More optimizations are planned, and some
benchmarks should be further improved, but at this point we're ready
to begin receiving bug reports. That will help prioritize the
remaining work for Swift 5.

Of the 656 public microbenchmarks in the Swift repository, there are
still several regressions larger than 10%:

TEST                    OLD      NEW      DELTA      RATIO
ClassArrayGetter2       139      1307     +840.3%    **0.11x**
HashTest                631      1233     +95.4%     **0.51x**
NopDeinit               21269    32389    +52.3%     **0.66x**
Hanoi                   1478     2166     +46.5%     **0.68x**
Calculator              127      158      +24.4%     **0.80x**
Dictionary3OfObjects    391      455      +16.4%     **0.86x**
CSVParsingAltIndices2   526      604      +14.8%     **0.87x**
Prims                   549      626      +14.0%     **0.88x**
CSVParsingAlt2          1252     1411     +12.7%     **0.89x**
Dictionary4OfObjects    206      232      +12.6%     **0.89x**
ArrayInClass            46       51       +10.9%     **0.90x**

The common pattern in these benchmarks is to define an array of data
as a class property and to repeatedly access that array through the
class reference. Each of those class property accesses now incurs a
runtime call. Naturally, introducing a runtime call in a loop that
otherwise does almost no work incurs substantial overhead. This is
similar to the issue caused by automatic reference counting. In some
cases, more sophistacated optimization will be able to determine the
same object is repeatedly accessed. Furthermore, the overhead of the
runtime call itself can be improved. But regardless of how well we
optimize, there will always a class of microbenchmarks in which the
runtime check has a noticeable impact.

As a general guideline, avoid performing class property access within
the most performance critical loops, particularly on different objects
in each loop iteration. If that isn't possible, it may help if the
visibility of those class properties is private or internal.

Author: atrick

cmake/modules/SwiftSource.cmake

@@ -245,8 +245,8 @@ function(_compile_swift_files
     list(APPEND swift_flags "-Xfrontend" "-enable-sil-ownership")
   endif()
 
-  if(SWIFT_ENABLE_STDLIBCORE_EXCLUSIVITY_CHECKING AND SWIFTFILE_IS_STDLIB)
-    list(APPEND swift_flags "-Xfrontend" "-enforce-exclusivity=checked")
+  if(NOT SWIFT_ENABLE_STDLIBCORE_EXCLUSIVITY_CHECKING AND SWIFTFILE_IS_STDLIB)
+    list(APPEND swift_flags "-Xfrontend" "-enforce-exclusivity=unchecked")
   endif()
 
   if(SWIFT_EMIT_SORTED_SIL_OUTPUT)

lib/Frontend/CompilerInvocation.cpp

@@ -770,8 +770,6 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
     Opts.VerifyExclusivity
       = A->getOption().matches(OPT_enable_verify_exclusivity);
   }
-  if (Opts.shouldOptimize() && !Opts.VerifyExclusivity)
-    Opts.EnforceExclusivityDynamic = false;
   if (const Arg *A = Args.getLastArg(options::OPT_enforce_exclusivity_EQ)) {
     parseExclusivityEnforcementOptions(A, Opts, Diags);
   }

test/IRGen/class_field_other_module.swift

@@ -1,7 +1,7 @@
 // RUN: %empty-directory(%t)
 
 // RUN: %target-swift-frontend -emit-module -emit-module-path=%t/other_class.swiftmodule %S/Inputs/other_class.swift
-// RUN: %target-swift-frontend -I %t -emit-ir -O %s | %FileCheck %s -DINT=i%target-ptrsize
+// RUN: %target-swift-frontend -I %t -emit-ir -O -enforce-exclusivity=unchecked %s | %FileCheck %s -DINT=i%target-ptrsize
 
 import other_class
 

test/SILOptimizer/array_contentof_opt.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -O -sil-verify-all -emit-sil  %s | %FileCheck %s
+// RUN: %target-swift-frontend -O -sil-verify-all -emit-sil -enforce-exclusivity=unchecked  %s | %FileCheck %s
 // REQUIRES: swift_stdlib_no_asserts,optimized_stdlib
 
 // This is an end-to-end test of the array(contentsOf) -> array(Element) optimization

test/SILOptimizer/bridged_casts_folding.swift

@@ -1,5 +1,5 @@
 
-// RUN: %target-swift-frontend -O -emit-sil %s | %FileCheck %s
+// RUN: %target-swift-frontend -O -emit-sil -enforce-exclusivity=unchecked %s | %FileCheck %s
 
 // REQUIRES: objc_interop
 

test/SILOptimizer/generic_specialization_loops_detection_with_loops.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -O -emit-sil -Xllvm -sil-print-generic-specialization-loops -Xllvm -sil-print-generic-specialization-info %s 2>&1 | %FileCheck --check-prefix=CHECK %s
+// RUN: %target-swift-frontend -O -emit-sil -enforce-exclusivity=unchecked -Xllvm -sil-print-generic-specialization-loops -Xllvm -sil-print-generic-specialization-info %s 2>&1 | %FileCheck --check-prefix=CHECK %s
 
 // Check that the generic specializer does not hang a compiler by
 // creating and infinite loop of generic specializations.

test/SILOptimizer/globalopt_global_propagation.swift

@@ -1,5 +1,5 @@
-// RUN: %target-swift-frontend  -O -emit-sil  %s | %FileCheck %s
-// RUN: %target-swift-frontend  -O -wmo -emit-sil  %s | %FileCheck -check-prefix=CHECK-WMO %s
+// RUN: %target-swift-frontend  -O -emit-sil -enforce-exclusivity=unchecked  %s | %FileCheck %s
+// RUN: %target-swift-frontend  -O -wmo -emit-sil -enforce-exclusivity=unchecked  %s | %FileCheck -check-prefix=CHECK-WMO %s
 
 // Check that values of internal and private global variables, which are provably assigned only 
 // once, are propagated into their uses and enable further optimizations like constant

test/SILOptimizer/globalopt_let_propagation.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend  -O -emit-sil -primary-file %s | %FileCheck %s
+// RUN: %target-swift-frontend  -O -emit-sil -enforce-exclusivity=unchecked -primary-file %s | %FileCheck %s
 
 // Check that values of static let and global let variables are propagated into their uses
 // and enable further optimizations like constant propagation, simplifications, etc.

test/SILOptimizer/illegal_escaping_address.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -O -sil-verify-all -emit-sil -parse-as-library %s
+// RUN: %target-swift-frontend -O -sil-verify-all -emit-sil -enforce-exclusivity=unchecked -parse-as-library %s
 
 // Check that the compiler does not crash for illegal escaping of an address
 // of a local variable.

test/SILOptimizer/let_propagation.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -primary-file %s  -emit-sil -O | %FileCheck %s
+// RUN: %target-swift-frontend -primary-file %s  -emit-sil -enforce-exclusivity=unchecked -O | %FileCheck %s
 
 // Check that LoadStoreOpts can handle "let" variables properly.
 // Such variables should be loaded only once and their loaded values can be reused.

test/SILOptimizer/optionset.swift

@@ -1,5 +1,5 @@
-// RUN: %target-swift-frontend  -parse-as-library -primary-file %s -O -sil-verify-all -module-name=test -emit-sil | %FileCheck %s
-// RUN: %target-swift-frontend  -parse-as-library -primary-file %s -Osize -sil-verify-all -module-name=test -emit-sil | %FileCheck %s
+// RUN: %target-swift-frontend  -parse-as-library -primary-file %s -O -sil-verify-all -module-name=test -emit-sil -enforce-exclusivity=unchecked | %FileCheck %s
+// RUN: %target-swift-frontend  -parse-as-library -primary-file %s -Osize -sil-verify-all -module-name=test -emit-sil -enforce-exclusivity=unchecked | %FileCheck %s
 // REQUIRES: swift_stdlib_no_asserts,optimized_stdlib
 
 public struct TestOptions: OptionSet {

test/SILOptimizer/outliner.swift

@@ -1,5 +1,5 @@
-// RUN: %target-swift-frontend -Osize -import-objc-header %S/Inputs/Outliner.h %s -emit-sil | %FileCheck %s
-// RUN: %target-swift-frontend -Osize -g -import-objc-header %S/Inputs/Outliner.h %s -emit-sil | %FileCheck %s
+// RUN: %target-swift-frontend -Osize -import-objc-header %S/Inputs/Outliner.h %s -emit-sil -enforce-exclusivity=unchecked | %FileCheck %s
+// RUN: %target-swift-frontend -Osize -g -import-objc-header %S/Inputs/Outliner.h %s -emit-sil -enforce-exclusivity=unchecked | %FileCheck %s
 
 // REQUIRES: objc_interop
 

test/SILOptimizer/sil_combine_protocol_conf.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend %s -O -wmo -emit-sil -Xllvm -sil-disable-pass=DeadFunctionElimination | %FileCheck %s
+// RUN: %target-swift-frontend %s -O -wmo -emit-sil -Xllvm -sil-disable-pass=DeadFunctionElimination -enforce-exclusivity=unchecked | %FileCheck %s
 
 // case 1: class protocol -- should optimize
 internal protocol SomeProtocol : class {

test/SILOptimizer/static_arrays.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend  -primary-file %s -O -sil-verify-all -Xllvm -sil-disable-pass=FunctionSignatureOpts -module-name=test -emit-sil | %FileCheck %s
+// RUN: %target-swift-frontend  -primary-file %s -O -sil-verify-all -Xllvm -sil-disable-pass=FunctionSignatureOpts -module-name=test -emit-sil -enforce-exclusivity=unchecked | %FileCheck %s
 
 // Also do an end-to-end test to check all components, including IRGen.
 // RUN: %empty-directory(%t)