Revert "Correctly emit dwoIDs after ASTFileSignature refactoring (D81347)"

This reverts commit a4c3ed4.

The test is curiously failing with a plain exit code 1 on Fuchsia.

Author: Teemperor

clang/include/clang/Basic/Module.h

@@ -62,15 +62,6 @@ struct ASTFileSignature : std::array<uint8_t, 20> {
 
   explicit operator bool() const { return *this != BaseT({{0}}); }
 
-  /// Returns the value truncated to the size of an uint64_t.
-  uint64_t truncatedValue() const {
-    uint64_t Value = 0;
-    static_assert(sizeof(*this) >= sizeof(uint64_t), "No need to truncate.");
-    for (unsigned I = 0; I < sizeof(uint64_t); ++I)
-      Value |= static_cast<uint64_t>((*this)[I]) << (I * 8);
-    return Value;
-  }
-
   static ASTFileSignature create(StringRef Bytes) {
     return create(Bytes.bytes_begin(), Bytes.bytes_end());
   }

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -2545,11 +2545,12 @@ llvm::DIModule *CGDebugInfo::getOrCreateModuleRef(ASTSourceDescriptor Mod,
     // We use the lower 64 bits for debug info.
 
     uint64_t Signature = 0;
-    if (const auto &ModSig = Mod.getSignature())
-      Signature = ModSig.truncatedValue();
-    else
+    if (const auto &ModSig = Mod.getSignature()) {
+      for (unsigned I = 0; I != sizeof(Signature); ++I)
+        Signature |= (uint64_t)ModSig[I] << (I * 8);
+    } else {
       Signature = ~1ULL;
-
+    }
     llvm::DIBuilder DIB(CGM.getModule());
     SmallString<0> PCM;
     if (!llvm::sys::path::is_absolute(Mod.getASTFile()))

clang/lib/CodeGen/ObjectFilePCHContainerOperations.cpp

@@ -250,10 +250,10 @@ class PCHContainerGenerator : public ASTConsumer {
     // PCH files don't have a signature field in the control block,
     // but LLVM detects DWO CUs by looking for a non-zero DWO id.
     // We use the lower 64 bits for debug info.
-
     uint64_t Signature =
-        Buffer->Signature ? Buffer->Signature.truncatedValue() : ~1ULL;
-
+        Buffer->Signature
+            ? (uint64_t)Buffer->Signature[1] << 32 | Buffer->Signature[0]
+            : ~1ULL;
     Builder->getModuleDebugInfo()->setDwoId(Signature);
 
     // Finalize the Builder.

clang/test/Modules/Inputs/DebugDwoId.h

@@ -357,10 +357,6 @@ module DebugObjCImport {
   }
 }
 
-module DebugDwoId {
-  header "DebugDwoId.h"
-}
-
 module ImportNameInDir {
   header "ImportNameInDir.h"
   export *