[ome] Just erase the destructure rather than trying to get rid of dead instructions due to simplifyInstruction.

This ensures that we do not run into any iterator invalidation issues. It does
worsen the passes output slightly, but avoiding the complexity is worth it and
other later passes will clean up the dead code.

rdar://55811732
(cherry picked from commit 1b29d86)

Author: gottesmm

lib/SILOptimizer/Transforms/OwnershipModelEliminator.cpp

@@ -285,9 +285,8 @@ static void splitDestructure(SILBuilder &B, SILInstruction *I, SILValue Op) {
     Result->replaceAllUsesWith(ProjInst);
   }
 
-  // We may have exposed trivially dead instructions due to
-  // simplifyInstruction... delete I and any such instructions!
-  recursivelyDeleteTriviallyDeadInstructions(I, true);
+  // Now that all of its uses have been eliminated, erase the destructure.
+  I->eraseFromParent();
 }
 
 bool OwnershipModelEliminatorVisitor::visitDestructureStructInst(

test/SILOptimizer/ownership_model_eliminator.sil

@@ -321,11 +321,24 @@ bb0(%0 : @owned $(Builtin.NativeObject, Builtin.Int32), %1 : @owned $TestArray2)
 
 // CHECK-LABEL: sil [canonical] @test_simplify_instruction : $@convention(thin) (@owned Builtin.NativeObject, Builtin.Int32) -> @owned Builtin.NativeObject {
 // CHECK: bb0([[ARG:%.*]] : $Builtin.NativeObject,
-// CHECK-NEXT:   return [[ARG]]
+// CHECK:   return [[ARG]]
 // CHECK: } // end sil function 'test_simplify_instruction'
 sil [canonical] [ossa] @test_simplify_instruction : $@convention(thin) (@owned Builtin.NativeObject, Builtin.Int32) -> @owned Builtin.NativeObject {
 bb0(%0 : @owned $Builtin.NativeObject, %1 : $Builtin.Int32):
   %2 = tuple(%0 : $Builtin.NativeObject, %1 : $Builtin.Int32)
   (%3, %4) = destructure_tuple %2 : $(Builtin.NativeObject, Builtin.Int32)
   return %3 : $Builtin.NativeObject
 }
+
+// Just make sure that we do not crash on this function.
+//
+// CHECK-LABEL: sil @do_not_crash_due_to_debug_value_use : $@convention(thin) (Builtin.Int32, Builtin.Int32) -> () {
+// CHECK: } // end sil function 'do_not_crash_due_to_debug_value_use'
+sil [ossa] @do_not_crash_due_to_debug_value_use : $@convention(thin) (Builtin.Int32, Builtin.Int32) -> () {
+bb0(%0a : $Builtin.Int32, %0b : $Builtin.Int32):
+  %0 = tuple(%0a : $Builtin.Int32, %0b : $Builtin.Int32)
+  (%1, %2) = destructure_tuple %0 : $(Builtin.Int32, Builtin.Int32)
+  debug_value %0 : $(Builtin.Int32, Builtin.Int32), let, name "myName2"
+  %9999 = tuple()
+  return %9999 : $()
+}