[DebugInfo] [SILGen] Remove invalid debug info from intermediates in prolog

Author: Snowy1803

lib/SILGen/SILGenProlog.cpp

@@ -1297,7 +1297,7 @@ void SILGenFunction::emitProlog(
 
   emitExpectedExecutor();
 
-  // IMPORTANT: This block should be the last one in `emitProlog`, 
+  // IMPORTANT: This block should be the last one in `emitProlog`,
   // since it terminates BB and no instructions should be insterted after it.
   // Emit an unreachable instruction if a parameter type is
   // uninhabited
@@ -1506,5 +1506,18 @@ uint16_t SILGenFunction::emitBasicProlog(
     B.createDebugValue(loc, undef.getValue(), dbgVar);
   }
 
+  for (auto &i : *B.getInsertionBB()) {
+    auto *alloc = dyn_cast<AllocStackInst>(&i);
+    if (!alloc)
+      continue;
+    auto varInfo = alloc->getVarInfo();
+    if (!varInfo || varInfo->ArgNo)
+      continue;
+    // The allocation has a varinfo but no argument number, which should not
+    // happen in the prolog. Unfortunately, some copies can generate wrong
+    // debug info, so we have to fix it here, by invalidating it.
+    alloc->invalidateVarInfo();
+  }
+
   return ArgNo;
 }

test/SILOptimizer/init_accessors.swift

@@ -330,7 +330,7 @@ struct TestGenericTuple<T, U> {
   //
   // CHECK: bb0([[A_REF:%.*]] : $*T, [[B_REF:%.*]] : $*(T, U), [[A_VALUE:%.*]] : $*T, [[B_VALUE:%.*]] : $*T, [[C_VALUE:%.*]] : $*U, [[METATYPE:%.*]] : $@thin TestGenericTuple<T, U>.Type):
   //
-  // CHECK: [[INIT_VALUE_1:%.*]] = alloc_stack $(T, U), let, name "initialValue"
+  // CHECK: [[INIT_VALUE_1:%.*]] = alloc_stack $(T, U)
   // CHECK-NEXT: [[INIT_VALUE_1_0:%.*]] = tuple_element_addr [[INIT_VALUE_1]] : $*(T, U), 0
   // CHECK-NEXT: copy_addr [take] [[B_VALUE]] to [init] [[INIT_VALUE_1_0]]
   // CHECK-NEXT: [[INIT_VALUE_1_1:%.*]] = tuple_element_addr [[INIT_VALUE_1]] : $*(T, U), 1