Fix least valid pointer value for 5.3 branch

lib/Driver/ToolChains.h

@@ -118,6 +118,9 @@ class LLVM_LIBRARY_VISIBILITY WebAssembly : public ToolChain {
                                      const JobContext &context) const override;
   InvocationInfo constructInvocation(const StaticLinkJobAction &job,
                                      const JobContext &context) const override;
+  void validateArguments(DiagnosticEngine &diags,
+                         const llvm::opt::ArgList &args,
+                         StringRef defaultTarget) const override;
 
 public:
   WebAssembly(const Driver &D, const llvm::Triple &Triple) : ToolChain(D, Triple) {}

lib/Driver/WebAssemblyToolChains.cpp

@@ -12,6 +12,8 @@
 
 #include "ToolChains.h"
 
+#include "swift/ABI/System.h"
+#include "swift/AST/DiagnosticsDriver.h"
 #include "swift/Basic/Dwarf.h"
 #include "swift/Basic/LLVM.h"
 #include "swift/Basic/Platform.h"
@@ -192,6 +194,15 @@ toolchains::WebAssembly::constructInvocation(const DynamicLinkJobAction &job,
     Arguments.push_back("-v");
   }
 
+  // WebAssembly doesn't reserve low addresses But without "extra inhabitants"
+  // of the pointer representation, runtime performance and memory footprint are
+  // worse. So assume that compiler driver uses wasm-ld and --global-base=1024
+  // to reserve low 1KB.
+  Arguments.push_back("-Xlinker");
+  Arguments.push_back(context.Args.MakeArgString(
+      Twine("--global-base=") +
+      std::to_string(SWIFT_ABI_WASM32_LEAST_VALID_POINTER)));
+
   // These custom arguments should be right before the object file at the end.
   context.Args.AddAllArgs(Arguments, options::OPT_linker_option_Group);
   context.Args.AddAllArgs(Arguments, options::OPT_Xlinker);
@@ -208,6 +219,23 @@ toolchains::WebAssembly::constructInvocation(const DynamicLinkJobAction &job,
   return II;
 }
 
+void validateLinkerArguments(DiagnosticEngine &diags,
+                             ArgStringList linkerArgs) {
+  for (auto arg : linkerArgs) {
+    if (StringRef(arg).startswith("--global-base=")) {
+      diags.diagnose(SourceLoc(), diag::error_option_not_supported, arg,
+                     "wasm32");
+    }
+  }
+}
+void toolchains::WebAssembly::validateArguments(DiagnosticEngine &diags,
+                                                const llvm::opt::ArgList &args,
+                                                StringRef defaultTarget) const {
+  ArgStringList linkerArgs;
+  args.AddAllArgValues(linkerArgs, options::OPT_Xlinker);
+  validateLinkerArguments(diags, linkerArgs);
+}
+
 ToolChain::InvocationInfo
 toolchains::WebAssembly::constructInvocation(const StaticLinkJobAction &job,
                                          const JobContext &context) const {

lib/IRGen/SwiftTargetInfo.cpp

@@ -140,6 +140,13 @@ static void configureSystemZ(IRGenModule &IGM, const llvm::Triple &triple,
   target.SwiftRetainIgnoresNegativeValues = true;
 }
 
+/// Configures target-specific information for wasm32 platforms.
+static void configureWasm32(IRGenModule &IGM, const llvm::Triple &triple,
+                            SwiftTargetInfo &target) {
+  target.LeastValidPointerValue =
+    SWIFT_ABI_WASM32_LEAST_VALID_POINTER;
+}
+
 /// Configure a default target.
 SwiftTargetInfo::SwiftTargetInfo(
   llvm::Triple::ObjectFormatType outputObjectFormat,
@@ -196,7 +203,9 @@ SwiftTargetInfo SwiftTargetInfo::get(IRGenModule &IGM) {
   case llvm::Triple::systemz:
     configureSystemZ(IGM, triple, target);
     break;
-
+  case llvm::Triple::wasm32:
+    configureWasm32(IGM, triple, target);
+    break;
   default:
     // FIXME: Complain here? Default target info is unlikely to be correct.
     break;

stdlib/public/SwiftShims/HeapObject.h

@@ -190,6 +190,22 @@ static_assert(alignof(HeapObject) == alignof(void*),
 #define _swift_BridgeObject_TaggedPointerBits                                  \
   (__swift_uintptr_t) SWIFT_ABI_DEFAULT_BRIDGEOBJECT_TAG_64
 
+#elif defined(__wasm32__)
+extern unsigned char __global_base;
+#define _swift_abi_LeastValidPointerValue                                      \
+  (__swift_uintptr_t) SWIFT_ABI_WASM32_LEAST_VALID_POINTER
+
+#define _swift_abi_SwiftSpareBitsMask                                          \
+  (__swift_uintptr_t) SWIFT_ABI_DEFAULT_SWIFT_SPARE_BITS_MASK
+
+#define _swift_abi_ObjCReservedBitsMask                                        \
+  (__swift_uintptr_t) SWIFT_ABI_DEFAULT_OBJC_RESERVED_BITS_MASK
+#define _swift_abi_ObjCReservedLowBits                                         \
+  (unsigned) SWIFT_ABI_DEFAULT_OBJC_NUM_RESERVED_LOW_BITS
+
+#define _swift_BridgeObject_TaggedPointerBits                                  \
+  (__swift_uintptr_t) SWIFT_ABI_DEFAULT_BRIDGEOBJECT_TAG_32
+
 #else
 
 #define _swift_abi_LeastValidPointerValue                                      \

stdlib/public/SwiftShims/System.h

@@ -192,4 +192,12 @@
 #define SWIFT_ABI_S390X_OBJC_WEAK_REFERENCE_MARKER_VALUE \
   (1<<SWIFT_ABI_S390X_OBJC_NUM_RESERVED_LOW_BITS)
 
+/*********************************** wasm32 ************************************/
+
+// WebAssembly doesn't reserve low addresses But without "extra inhabitants" of
+// the pointer representation, runtime performance and memory footprint are
+// worse. So assume that compiler driver uses wasm-ld and --global-base=1024 to
+// reserve low 1KB.
+#define SWIFT_ABI_WASM32_LEAST_VALID_POINTER 1024
+
 #endif // SWIFT_STDLIB_SHIMS_ABI_SYSTEM_H