[move-function] Propagate debug_value undef rather than treat it as an invalidation.

The reason that I am doing this is that otherwise in funclets we may show an
invalidated value being available if we have an llvm.dbg.addr for a reinit value
later in the funclet. This ensures that we have the undef at the beginning of
the funclet so before that llvm.dbg.addr we will properly show no value.

Author: gottesmm

lib/SILOptimizer/Mandatory/DebugInfoCanonicalizer.cpp

@@ -214,16 +214,6 @@ bool DebugInfoCanonicalizer::process() {
           continue;
         }
 
-        // If we have a SILUndef, mark this debug info as being mapped to
-        // nullptr.
-        if (isa<SILUndef>(dvi->getOperand())) {
-          LLVM_DEBUG(llvm::dbgs() << "        SILUndef.\n");
-          auto iter = state.debugValues.insert({*debugInfo, nullptr});
-          if (!iter.second)
-            iter.first->second = nullptr;
-          continue;
-        }
-
         // Otherwise, we may have a new debug_value to track. Try to begin
         // tracking it...
         auto iter = state.debugValues.insert({*debugInfo, dvi});

test/DebugInfo/move_function_dbginfo_async.swift

@@ -146,6 +146,8 @@ public func letSimpleTest<T>(_ msg: __owned T) async {
 // DWARF-NEXT:    [0x{{[a-f0-9]+}}, 0x{{[a-f0-9]+}}):
 // DWARF-SAME:        DW_OP_entry_value(DW_OP_reg14 R14), DW_OP_plus_uconst 0x[[MSG_LOC]], DW_OP_plus_uconst 0x8, DW_OP_deref
 // DWARF-NEXT:    [0x{{[a-f0-9]+}}, 0x{{[a-f0-9]+}})
+// DWARF-SAME:        DW_OP_breg{{.*}}, DW_OP_deref, DW_OP_plus_uconst 0x[[MSG_LOC]], DW_OP_plus_uconst 0x8, DW_OP_deref
+// DWARF-NEXT:    [0x{{[a-f0-9]+}}, 0x{{[a-f0-9]+}})
 // DWARF-SAME:        DW_OP_breg{{.*}}, DW_OP_deref, DW_OP_plus_uconst 0x[[MSG_LOC]], DW_OP_plus_uconst 0x8, DW_OP_deref)
 // DWARF-NEXT: DW_AT_name	("msg")
 //

test/SILOptimizer/debuginfo_canonicalizer.sil

@@ -113,6 +113,7 @@ bb3:
 // CHECK: [[BB_RHS]]:
 // CHECK-NEXT:   debug_value [moved] undef
 // CHECK-NEXT:   abort_apply
+// CHECK-NEXT:   debug_value [moved] undef
 // CHECK-NEXT:   br [[BB_CONT]]
 // CHECK: } // end sil function 'testUndefDiamond'
 sil @testUndefDiamond : $@convention(thin) (@guaranteed Klass) -> () {