[LTO] Improve diagnostics handling when parsing module-level inline assembly (#75726)

Non-LTO compiles set the buffer name to "<inline asm>"
(`AsmPrinter::addInlineAsmDiagBuffer`) and pass diagnostics to
`ClangDiagnosticHandler` (through the `MCContext` handler in
`MachineModuleInfoWrapperPass::doInitialization`) to ensure that
the exit code is 1 in the presence of errors. In contrast, LTO compiles
spuriously succeed even if error messages are printed.

```
% cat a.c
void _start() {}
asm("unknown instruction");
% clang -c a.c
<inline asm>:1:1: error: invalid instruction mnemonic 'unknown'
    1 | unknown instruction
      | ^
1 error generated.
% clang -c -flto a.c; echo $?  # -flto=thin is the same
error: invalid instruction mnemonic 'unknown'
unknown instruction
^~~~~~~
error: invalid instruction mnemonic 'unknown'
unknown instruction
^~~~~~~
0
```

`CollectAsmSymbols` parses inline assembly and is transitively called by
both `ModuleSummaryIndexAnalysis::run` and `WriteBitcodeToFile`, leading
to duplicate diagnostics.

This patch updates `CollectAsmSymbols` to be similar to non-LTO
compiles.
```
% clang -c -flto=thin a.c; echo $?
<inline asm>:1:1: error: invalid instruction mnemonic 'unknown'
    1 | unknown instruction
      | ^
1 errors generated.
1
```

The `HasErrors` check does not prevent duplicate warnings but assembler
warnings are very uncommon.

Author: MaskRay

clang/lib/CodeGen/CodeGenAction.cpp

@@ -418,6 +418,8 @@ void BackendConsumer::anchor() { }
 } // namespace clang
 
 bool ClangDiagnosticHandler::handleDiagnostics(const DiagnosticInfo &DI) {
+  if (DI.getSeverity() == DS_Error)
+    HasErrors = true;
   BackendCon->DiagnosticHandlerImpl(DI);
   return true;
 }

clang/test/CodeGen/invalid_global_asm.c

@@ -1,5 +1,10 @@
 // REQUIRES: arm-registered-target
 // RUN: not %clang_cc1 -emit-obj -triple armv6-unknown-unknown -o %t %s 2>&1 | FileCheck %s
+// RUN: not %clang_cc1 -emit-obj -triple armv6-unknown-unknown -flto -o %t %s 2>&1 | FileCheck %s
+
+/// Test the diagnostic behavior considering the whole system including the driver.
+// RUN: not %clang --target=armv6-unknown-unknown -c -flto=thin -o %t %s 2>&1 | FileCheck %s
 #pragma clang diagnostic ignored "-Wmissing-noreturn"
 __asm__(".Lfoo: movw r2, #:lower16:.Lbar - .Lfoo");
 // CHECK: <inline asm>:1:8: error: instruction requires: armv6t2
+// CHECK-NOT: error:

lld/test/MachO/lto-module-asm-err.ll

@@ -3,13 +3,11 @@
 ; RUN: not %lld %t.bc -o /dev/null 2>&1 | FileCheck %s --check-prefix=REGULAR
 
 ;; For regular LTO, the original module name is lost.
-;; TODO Fix the line number
-; REGULAR: error: ld-temp.o <inline asm>:3:1: invalid instruction mnemonic 'invalid'
+; REGULAR: error: <inline asm>:2:1: invalid instruction mnemonic 'invalid'
 
-; RUN: opt -module-summary %s -o %t.bc
-; RUN: not %lld %t.bc -o /dev/null 2>&1 | FileCheck %s --check-prefix=THIN
+; RUN: not opt -module-summary %s -o /dev/null 2>&1 | FileCheck %s --check-prefix=THIN
 
-; THIN: error: {{.*}}.bc <inline asm>:2:1: invalid instruction mnemonic 'invalid'
+; THIN: error: <inline asm>:2:1: invalid instruction mnemonic 'invalid'
 
 target triple = "x86_64-apple-macosx10.15.0"
 target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"

llvm/include/llvm/IR/DiagnosticHandler.h

@@ -23,6 +23,7 @@ class DiagnosticInfo;
 /// which remarks are enabled.
 struct DiagnosticHandler {
   void *DiagnosticContext = nullptr;
+  bool HasErrors = false;
   DiagnosticHandler(void *DiagContext = nullptr)
       : DiagnosticContext(DiagContext) {}
   virtual ~DiagnosticHandler() = default;

llvm/lib/Object/ModuleSymbolTable.cpp

@@ -16,6 +16,7 @@
 #include "RecordStreamer.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalAlias.h"
 #include "llvm/IR/GlobalValue.h"
@@ -68,6 +69,11 @@ void ModuleSymbolTable::addModule(Module *M) {
 static void
 initializeRecordStreamer(const Module &M,
                          function_ref<void(RecordStreamer &)> Init) {
+  // This function may be called twice, once for ModuleSummaryIndexAnalysis and
+  // the other when writing the IR symbol table. If parsing inline assembly has
+  // caused errors in the first run, suppress the second run.
+  if (M.getContext().getDiagHandlerPtr()->HasErrors)
+    return;
   StringRef InlineAsm = M.getModuleInlineAsm();
   if (InlineAsm.empty())
     return;
@@ -95,7 +101,8 @@ initializeRecordStreamer(const Module &M,
   if (!MCII)
     return;
 
-  std::unique_ptr<MemoryBuffer> Buffer(MemoryBuffer::getMemBuffer(InlineAsm));
+  std::unique_ptr<MemoryBuffer> Buffer(
+      MemoryBuffer::getMemBuffer(InlineAsm, "<inline asm>"));
   SourceMgr SrcMgr;
   SrcMgr.AddNewSourceBuffer(std::move(Buffer), SMLoc());
 
@@ -115,6 +122,13 @@ initializeRecordStreamer(const Module &M,
   if (!TAP)
     return;
 
+  MCCtx.setDiagnosticHandler([&](const SMDiagnostic &SMD, bool IsInlineAsm,
+                                 const SourceMgr &SrcMgr,
+                                 std::vector<const MDNode *> &LocInfos) {
+    M.getContext().diagnose(
+        DiagnosticInfoSrcMgr(SMD, M.getName(), IsInlineAsm, /*LocCookie=*/0));
+  });
+
   // Module-level inline asm is assumed to use At&t syntax (see
   // AsmPrinter::doInitialization()).
   Parser->setAssemblerDialect(InlineAsm::AD_ATT);