WebAssembly: fix GOT-relative pointers without PCrel

Previous commits changed a bunch of relative pointers to absolute
in the metadata; at the time I didn't add support for adding tag
bits, which signifies if the pointers point to the .got section
(and thus needs an extra layer of indirection.)

This broke _isCImportedTagType on $ss7UnicodeO5ASCIIOMn,
so this commit adds back tag support for metadata pointers.

Author: zhuowei

lib/IRGen/ConstantBuilder.h

@@ -99,7 +99,15 @@ class ConstantAggregateBuilderBase
       // WebAssembly: hack: doesn't support PCrel data relocations
       // also, we should set the lowest bit, but I don't know how to do that
       // there's no GOT on WebAssembly anyways though
-      add(llvm::ConstantExpr::getPtrToInt(reference.getValue(), IGM().RelativeAddressTy, false));
+
+
+      llvm::Constant *offset = llvm::ConstantExpr::getPtrToInt(reference.getValue(), IGM().RelativeAddressTy, false);
+      // borrowed from addTaggedRelativeOffset
+      unsigned tag = unsigned(reference.isIndirect());
+      if (tag) {
+        offset = llvm::ConstantExpr::getAdd(offset, llvm::ConstantInt::get(IGM().RelativeAddressTy, tag));
+      }
+      add(offset);
       return;
     }
     addTaggedRelativeOffset(IGM().RelativeAddressTy,

lib/IRGen/GenMeta.cpp

@@ -4337,7 +4337,12 @@ GenericRequirementsMetadata irgen::addGenericRequirements(
           // WebAssembly: hack: Wasm doesn't support PC-relative offsets.
           // also doesn't handle tag yet
           if (IGM.TargetInfo.OutputObjectFormat == llvm::Triple::Wasm) {
-            B.add(llvm::ConstantExpr::getPtrToInt(descriptorRef.getValue(), IGM.RelativeAddressTy, false));
+            llvm::Constant *offset = llvm::ConstantExpr::getPtrToInt(descriptorRef.getValue(), IGM.RelativeAddressTy, false);
+            // borrowed from addTaggedRelativeOffset
+            if (tag) {
+                offset = llvm::ConstantExpr::getAdd(offset, llvm::ConstantInt::get(IGM.RelativeAddressTy, tag));
+            }
+            B.add(offset);
             return;
           }