[ARM/AArch64] Enforce alignment for bitfielded structs

When creating a global variable with a type of a struct with bitfields, we must
forcibly set the alignment of the global from the RecordDecl. We must do this so
that the proper bitfield alignment makes its way down to LLVM, since clang will
mangle the bitfields into one large type.

llvm-svn: 235976

1 files changed, 17 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index c517d17666d..861a6ee164e 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1799,6 +1799,23 @@ CodeGenModule::GetOrCreateLLVMGlobal(StringRef MangledName,
         D->getType().isConstant(Context) &&
         isExternallyVisible(D->getLinkageAndVisibility().getLinkage()))
       GV->setSection(".cp.rodata");
+
+    // The ARM/AArch64 ABI expects structs with bitfields to respect the proper
+    // container alignment, hence we have to enfore this in the IR so as to
+    // work around clang combining bitfields into one large type.
+    if (getContext().getTargetInfo().enforceBitfieldContainerAlignment()) {
+      if (const auto *RT = D->getType()->getAs<RecordType>()) {
+        const RecordDecl *RD = RT->getDecl();
+
+        for (auto I = RD->field_begin(), End = RD->field_end(); I != End; ++I) {
+          if ((*I)->isBitField()) {
+            const ASTRecordLayout &Info = getContext().getASTRecordLayout(RD);
+            GV->setAlignment(Info.getAlignment().getQuantity());
+            break;
+          }
+        }
+      }
+    }
   }
 
   if (AddrSpace != Ty->getAddressSpace())