[clang-repl] Extend the C support.

The IdResolver chain is the main way for C to implement lookup rules. Every new
partial translation unit caused clang to exit the top-most scope which in turn
cleaned up the IdResolver chain. That was not an issue for C++ because its
lookup is implemented on the level of declaration contexts.

This patch keeps the IdResolver chain across partial translation units
maintaining proper C-style lookup infrastructure.

clang/lib/Interpreter/IncrementalParser.cpp

@@ -387,8 +387,7 @@ std::unique_ptr<llvm::Module> IncrementalParser::GenModule() {
 
 void IncrementalParser::CleanUpPTU(PartialTranslationUnit &PTU) {
   TranslationUnitDecl *MostRecentTU = PTU.TUPart;
-  TranslationUnitDecl *FirstTU = MostRecentTU->getFirstDecl();
-  if (StoredDeclsMap *Map = FirstTU->getPrimaryContext()->getLookupPtr()) {
+  if (StoredDeclsMap *Map = MostRecentTU->getPrimaryContext()->getLookupPtr()) {
     for (auto &&[Key, List] : *Map) {
       DeclContextLookupResult R = List.getLookupResult();
       std::vector<NamedDecl *> NamedDeclsToRemove;
@@ -407,6 +406,16 @@ void IncrementalParser::CleanUpPTU(PartialTranslationUnit &PTU) {
       }
     }
   }
+
+  // FIXME: We should de-allocate MostRecentTU
+  for (Decl *D : MostRecentTU->decls()) {
+    auto *ND = dyn_cast<NamedDecl>(D);
+    if (!ND)
+      continue;
+    // Check if we need to clean up the IdResolver chain.
+    if (ND->getDeclName().getFETokenInfo())
+      getCI()->getSema().IdResolver.RemoveDecl(ND);
+  }
 }
 
 llvm::StringRef IncrementalParser::GetMangledName(GlobalDecl GD) const {

clang/lib/Sema/SemaDecl.cpp

@@ -2280,9 +2280,13 @@ void Sema::ActOnPopScope(SourceLocation Loc, Scope *S) {
     if (LabelDecl *LD = dyn_cast<LabelDecl>(D))
       CheckPoppedLabel(LD, *this, addDiag);
 
-    // Remove this name from our lexical scope, and warn on it if we haven't
-    // already.
-    IdResolver.RemoveDecl(D);
+    // Partial translation units that are created in incremental processing must
+    // not clean up the IdResolver because PTUs should take into account the
+    // declarations that came from previous PTUs.
+    if (!PP.isIncrementalProcessingEnabled())
+      IdResolver.RemoveDecl(D);
+
+    // Warn on it if we are shadowing a declaration.
     auto ShadowI = ShadowingDecls.find(D);
     if (ShadowI != ShadowingDecls.end()) {
       if (const auto *FD = dyn_cast<FieldDecl>(ShadowI->second)) {

clang/test/Interpreter/execute.c

@@ -0,0 +1,21 @@
+// REQUIRES: host-supports-jit
+// UNSUPPORTED: system-aix
+
+// RUN: cat %s | clang-repl -Xcc -xc -Xcc -Xclang -Xcc -verify | FileCheck %s
+// RUN: cat %s | clang-repl -Xcc -xc -Xcc -O2 -Xcc -Xclang -Xcc -verify| FileCheck %s
+int printf(const char *, ...);
+int i = 42; err // expected-error{{use of undeclared identifier}}
+int i = 42;
+struct S { float f; struct S *m;} s = {1.0, 0};
+// FIXME: Making foo inline fails to emit the function.
+int foo() { return 42; }
+void run() {                                                    \
+  printf("i = %d\n", i);                                        \
+  printf("S[f=%f, m=0x%llx]\n", s.f, (unsigned long long)s.m);  \
+  int r3 = foo();                                               \
+}
+run();
+// CHECK: i = 42
+// CHECK-NEXT: S[f=1.000000, m=0x0]
+
+%quit