Explicitly initialize opaque pointer mode in CodeGenAction

Explicitly call `LLVMContext::setOpaquePointers` in `CodeGenAction`
before loading any IR files. With this we use the mode specified on the
command-line rather than lazily initializing it based on the contents of
the IR.

This helps when using `-fthinlto-index` which may end up mixing files
with typed and opaque pointer types which fails when the first file
happened to use typed pointers since we cannot downgrade IR with opaque
pointer types to typed pointer types.

Differential Revision: https://reviews.llvm.org/D137475

clang/lib/CodeGen/CodeGenAction.cpp

@@ -1102,6 +1102,8 @@ CodeGenAction::loadModule(MemoryBufferRef MBRef) {
   CompilerInstance &CI = getCompilerInstance();
   SourceManager &SM = CI.getSourceManager();
 
+  VMContext->setOpaquePointers(CI.getCodeGenOpts().OpaquePointers);
+
   // For ThinLTO backend invocations, ensure that the context
   // merges types based on ODR identifiers. We also need to read
   // the correct module out of a multi-module bitcode file.

clang/test/CodeGen/Inputs/thinlto-opaque.ll

@@ -0,0 +1,6 @@
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64--"
+
+define ptr @f2() {
+  ret ptr null
+}

clang/test/CodeGen/thinlto-distributed-cfi-devirt.ll

@@ -100,7 +100,7 @@ cont2:
   ; CHECK-IR: br i1 {{.*}}, label %trap
 
   ; We still have to call it as virtual.
-  ; CHECK-IR: %call3 = tail call i32 %7
+  ; CHECK-IR: %call3 = tail call i32 {{%[0-9]+}}
   %call3 = tail call i32 %8(%struct.A* nonnull %obj, i32 %call)
   ret i32 %call3
 }

clang/test/CodeGen/thinlto-opaque-typed-mix.ll

@@ -0,0 +1,23 @@
+; REQUIRES: x86-registered-target
+; Test that mixing bitcode file with opaque and typed pointers works.
+
+; RUN: mkdir -p %t
+; RUN: opt -module-summary -o %t/typed.bc %s
+; RUN: opt -module-summary -o %t/opaque.bc %S/Inputs/thinlto-opaque.ll
+; RUN: llvm-lto2 run -thinlto-distributed-indexes %t/typed.bc %t/opaque.bc \
+; RUN:   -o %t/native.o -r %t/typed.bc,main,plx -r %t/typed.bc,f2, \
+; RUN:   -r %t/opaque.bc,f2,p
+
+; RUN: %clang_cc1 -triple x86_64-- -emit-obj -o %t/native.o %t/typed.bc \
+; RUN:   -Wno-override-module \
+; RUN:   -fthinlto-index=%t/typed.bc.thinlto.bc
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64--"
+
+declare i8* @f2()
+
+define i32 @main() {
+  call i8* @f2()
+  ret i32 0
+}