Fix verifier error in CastOptimizer

While removing an invalid cast and inserting traps, we are currently
inserting a store of undef to the cast destination and delete all
instructions after the cast except for dealloc_stack.
If the cast destination was an alloc_stack, the verifier could raise
an error saying the cast destination was initialized at the dealloc.

This PR deletes the store to undef, destroy_addr of the cast src,
and gets rid of the code that was retaining the dealloc_stack.
None of this is necessary anymore and the SIL is going to be legal
because we insert unreachable instruction.

Author: meg-gupta

lib/SILOptimizer/Utils/CastOptimizer.cpp

@@ -1496,11 +1496,6 @@ void CastOptimizer::deleteInstructionsAfterUnreachable(
   while (UnreachableInstIt != Block->end()) {
     SILInstruction *CurInst = &*UnreachableInstIt;
     ++UnreachableInstIt;
-    if (auto *DeallocStack = dyn_cast<DeallocStackInst>(CurInst))
-      if (!isa<SILUndef>(DeallocStack->getOperand())) {
-        DeallocStack->moveBefore(TrapInst);
-        continue;
-      }
     CurInst->replaceAllUsesOfAllResultsWithUndef();
     eraseInstAction(CurInst);
   }
@@ -1622,17 +1617,6 @@ SILInstruction *CastOptimizer::optimizeUnconditionalCheckedCastAddrInst(
     // Remove the cast and insert a trap, followed by an
     // unreachable instruction.
     SILBuilderWithScope Builder(Inst, builderContext);
-    // mem2reg's invariants get unhappy if we don't try to
-    // initialize a loadable result.
-    if (!dynamicCast.getTargetLoweredType().isAddressOnly(
-            Builder.getFunction())) {
-      auto undef = SILValue(
-          SILUndef::get(dynamicCast.getTargetLoweredType().getObjectType(),
-                        Builder.getFunction()));
-      Builder.emitStoreValueOperation(Loc, undef, dynamicCast.getDest(),
-                                      StoreOwnershipQualifier::Init);
-    }
-    Builder.emitDestroyAddr(Loc, Inst->getSrc());
     auto *TrapI = Builder.createBuiltinTrap(Loc);
     eraseInstAction(Inst);
     Builder.setInsertionPoint(std::next(TrapI->getIterator()));

test/SIL/Parser/basic.sil

@@ -1583,10 +1583,10 @@ bb0(%0 : $Builtin.RawPointer, %1 : $Builtin.Word):
   return %28 : $()
 }
 
-// CHECK-LABEL: sil @test_end_lifetime : $@convention(thin) (@owned Builtin.NativeObject) -> () {
+// CHECK-LABEL: sil [ossa] @test_end_lifetime : $@convention(thin) (@owned Builtin.NativeObject) -> () {
 // CHECK: end_lifetime {{%.*}} : $Builtin.NativeObject
-sil @test_end_lifetime : $@convention(thin) (@owned Builtin.NativeObject) -> () {
-bb0(%0 : $Builtin.NativeObject):
+sil [ossa] @test_end_lifetime : $@convention(thin) (@owned Builtin.NativeObject) -> () {
+bb0(%0 : @owned $Builtin.NativeObject):
   end_lifetime %0 : $Builtin.NativeObject
   return undef : $()
 }

test/SILOptimizer/constant_propagation.sil

@@ -700,8 +700,6 @@ class AnObject {}
 // CHECK-LABEL: sil @replace_unconditional_check_cast_failure
 // CHECK:  bb2:
 // CHECK:  alloc_stack $AnObject
-// CHECK:  store undef to %0
-// CHECK:  dealloc_stack
 // CHECK:  builtin "int_trap"()
 // CHECK:  unreachable
 

test/SILOptimizer/constant_propagation_ownership.sil

@@ -875,8 +875,6 @@ class AnSubObject : AnObject {}
 // CHECK-LABEL: sil [ossa] @replace_unconditional_check_cast_failure
 // CHECK:  bb2:
 // CHECK:  alloc_stack $AnObject
-// CHECK:  store undef to [trivial] %0
-// CHECK:  dealloc_stack
 // CHECK:  builtin "int_trap"()
 // CHECK:  unreachable
 

test/SILOptimizer/sil_combine_uncheck.sil

@@ -38,8 +38,6 @@ bb0(%0 : $Builtin.Int1):
 
 // CHECK-LABEL: sil @test_unconditional_checked_cast_addr_fail
 // CHECK: bb0
-// CHECK-NEXT: store undef
-// CHECK-NEXT: destroy_addr
 // CHECK-NEXT: builtin "int_trap"
 // CHECK: unreachable
 // CHECK: }

test/SILOptimizer/sil_combine_uncheck_ossa.sil

@@ -38,8 +38,6 @@ bb0(%0 : $Builtin.Int1):
 
 // CHECK-LABEL: sil [ossa] @test_unconditional_checked_cast_addr_fail
 // CHECK: bb0
-// CHECK-NEXT: store undef
-// CHECK-NEXT: destroy_addr
 // CHECK-NEXT: builtin "int_trap"
 // CHECK: unreachable
 // CHECK: }