SimplifyInstructions: don't remove empty access scopes

Empty access scopes can be a result of e.g. redundant-load-elimination.
It's still important to keep those access scopes to detect access violations.
Even if the load is physically not done anymore, in case of a conflicting access a propagated load is still wrong and must be detected.

rdar://164571252

Author: eeckstein

lib/SILOptimizer/Analysis/SimplifyInstruction.cpp

@@ -64,7 +64,6 @@ namespace {
     SILValue
     visitUncheckedTrivialBitCastInst(UncheckedTrivialBitCastInst *UTBCI);
     SILValue visitEndCOWMutationInst(EndCOWMutationInst *ECM);
-    SILValue visitBeginAccessInst(BeginAccessInst *BAI);
     SILValue visitMetatypeInst(MetatypeInst *MTI);
     SILValue visitConvertFunctionInst(ConvertFunctionInst *cfi);
 
@@ -419,16 +418,6 @@ visitUncheckedBitwiseCastInst(UncheckedBitwiseCastInst *UBCI) {
   return SILValue();
 }
 
-SILValue InstSimplifier::visitBeginAccessInst(BeginAccessInst *BAI) {
-  // Remove "dead" begin_access.
-  if (llvm::all_of(BAI->getUses(), [](Operand *operand) -> bool {
-        return isIncidentalUse(operand->getUser());
-      })) {
-    return BAI->getOperand();
-  }
-  return SILValue();
-}
-
 SILValue InstSimplifier::visitConvertFunctionInst(ConvertFunctionInst *cfi) {
   // Eliminate round trip convert_function. Non round-trip is performed in
   // SILCombine.

test/SILOptimizer/sil_simplify_instrs.sil

@@ -325,34 +325,18 @@ public class B {
   deinit
 }
 
-// simplify access markers
-sil @simplify_accesssil : $@convention(method) (@guaranteed A) -> () {
+// CHECK-LABEL: sil @dont_remove_empty_access_scopes : $@convention(method) (@guaranteed A) -> () {
+// CHECK:         begin_access
+// CHECK-LABEL: } // end sil function 'dont_remove_empty_access_scopes'
+sil @dont_remove_empty_access_scopes : $@convention(method) (@guaranteed A) -> () {
 bb0(%0 : $A):
   %badr = ref_element_addr %0 : $A, #A.b
   %ba1 = begin_access [read] [dynamic] %badr : $*B
   end_access %ba1 : $*B
-  %ba2 = begin_access [read] [dynamic] %badr : $*B
-  fix_lifetime %ba2 : $*B
-  end_access %ba2 : $*B
-  %ba3 = begin_access [read] [dynamic] %badr : $*B
-  %b = load %ba3 : $*B
-  end_access %ba3 : $*B
-  %xadr = ref_element_addr %b : $B, #B.x
-  %xaccess = begin_access [read] [dynamic] %xadr : $*Int
-  end_access %xaccess : $*Int
-
   %r = tuple ()
   return %r : $()
 }
 
-// CHECK-LABEL: sil @simplify_accesssil : $@convention(method) (@guaranteed A) -> () {
-// CHECK: bb0(%0 : $A):
-// CHECK-NEXT: [[ADR:%.*]] = ref_element_addr %0 : $A, #A.b
-// CHECK-NEXT: fix_lifetime [[ADR]] : $*B
-// CHECK-NEXT: %{{.*}} = tuple ()
-// CHECK-NEXT: return %{{.*}} : $()
-// CHECK-LABEL: } // end sil function 'simplify_accesssil'
-
 // Test replacement of metatype instructions with metatype arguments.
 protocol SomeP {}
 

test/SILOptimizer/sil_simplify_instrs_ossa.sil

@@ -370,31 +370,14 @@ public class B {
 
 // simplify access markers
 
-// CHECK-LABEL: sil [ossa] @simplify_accesssil : $@convention(method) (@guaranteed A) -> () {
-// CHECK: bb0(%0 : @guaranteed $A):
-// CHECK-NEXT: [[ADR:%.*]] = ref_element_addr %0 : $A, #A.b
-// CHECK-NEXT: fix_lifetime [[ADR]] : $*B
-// CHECK-NEXT: %{{.*}} = tuple ()
-// CHECK-NEXT: return %{{.*}} : $()
-// CHECK: } // end sil function 'simplify_accesssil'
-sil [ossa] @simplify_accesssil : $@convention(method) (@guaranteed A) -> () {
+// CHECK-LABEL: sil [ossa] @dont_remove_empty_access_scopes : $@convention(method) (@guaranteed A) -> () {
+// CHECK:         begin_access
+// CHECK:       } // end sil function 'dont_remove_empty_access_scopes'
+sil [ossa] @dont_remove_empty_access_scopes : $@convention(method) (@guaranteed A) -> () {
 bb0(%0 : @guaranteed $A):
   %badr = ref_element_addr %0 : $A, #A.b
   %ba1 = begin_access [read] [dynamic] %badr : $*B
   end_access %ba1 : $*B
-  %ba2 = begin_access [read] [dynamic] %badr : $*B
-  fix_lifetime %ba2 : $*B
-  end_access %ba2 : $*B
-  %ba3 = begin_access [read] [dynamic] %badr : $*B
-  %b = load [copy] %ba3 : $*B
-  end_access %ba3 : $*B
-  %bb = begin_borrow %b : $B
-  %xadr = ref_element_addr %bb : $B, #B.x
-  %xaccess = begin_access [read] [dynamic] %xadr : $*Int
-  end_access %xaccess : $*Int
-  end_borrow %bb : $B
-  destroy_value %b : $B
-
   %r = tuple ()
   return %r : $()
 }