Prepare IRGen and LLVM passes to use the new preserve_most calling convention, but do not enable it yet.

The convention should be enabled once we can properly build the runtime library using Siwft's own clang/llvm binaries.

Author: swiftix

include/swift/Runtime/Config.h

@@ -104,6 +104,9 @@
 #define SWIFT_CC_DefaultCC_IMPL SWIFT_CC_c
 #define SWIFT_LLVM_CC_DefaultCC llvm::CallingConv::C
 
+#define SWIFT_LLVM_CC_RegisterPreservingCC llvm::CallingConv::PreserveMost
+
+
 // If defined, it indicates that runtime function wrappers
 // should be used on all platforms, even they do not support
 // the new calling convention which requires this.
@@ -113,13 +116,19 @@
 // supported by the current target.
 // TODO: Define it once the runtime calling convention support has
 // been integrated into clang and llvm.
-//#define RT_USE_RegisterPreservingCC
+#define SWIFT_RT_USE_RegisterPreservingCC 0
+
+#if  __has_attribute(preserve_most)
+#define SWIFT_BACKEND_SUPPORTS_RegisterPreservingCC 1
+#else
+#define SWIFT_BACKEND_SUPPORTS_RegisterPreservingCC 0
+#endif
+
 
 // RegisterPreservingCC is a dedicated runtime calling convention to be used
 // when calling the most popular runtime functions.
-#if defined(RT_USE_RegisterPreservingCC) && __has_attribute(preserve_most) &&  \
-    (defined(__aarch64__) || defined(__x86_64__))
-
+#if SWIFT_RT_USE_RegisterPreservingCC &&                              \
+    SWIFT_BACKEND_SUPPORTS_RegisterPreservingCC && defined(__aarch64__)
 // Targets supporting the dedicated runtime convention should use it.
 // If a runtime function is using this calling convention, it can
 // be invoked only by means of a wrapper, which performs an indirect
@@ -134,7 +143,6 @@
   SWIFT_CC_preserve_most
 #define SWIFT_CC_RegisterPreservingCC_IMPL                     \
   SWIFT_CC_preserve_most
-#define SWIFT_LLVM_CC_RegisterPreservingCC llvm::CallingConv::PreserveMost
 
 // Indicate that wrappers should be used, because it is required
 // for the calling convention to get around dynamic linking issues.
@@ -147,7 +155,6 @@
 // No wrappers are required in this case by the calling convention.
 #define SWIFT_CC_RegisterPreservingCC SWIFT_CC_c
 #define SWIFT_CC_RegisterPreservingCC_IMPL SWIFT_CC_c
-#define SWIFT_LLVM_CC_RegisterPreservingCC llvm::CallingConv::C
 
 #endif
 
@@ -171,6 +178,7 @@
 #define SWIFT_RT_ENTRY_REF_AS_STR(Name) "_" #Name
 
 #if defined(SWIFT_RT_USE_WRAPPERS_ALWAYS)
+#undef SWIFT_RT_USE_WRAPPERS
 #define SWIFT_RT_USE_WRAPPERS
 #endif
 

lib/IRGen/IRGenModule.cpp

@@ -375,11 +375,13 @@ IRGenModule::IRGenModule(IRGenModuleDispatcher &dispatcher, SourceFile *SF,
 
   // Only use the new calling conventions on platforms that support it.
   auto Arch = Triple.getArch();
-  if (Arch == llvm::Triple::ArchType::x86_64 ||
-      Arch == llvm::Triple::ArchType::aarch64)
+  if (SWIFT_RT_USE_RegisterPreservingCC &&
+      Arch == llvm::Triple::ArchType::aarch64) {
     RegisterPreservingCC = SWIFT_LLVM_CC(RegisterPreservingCC);
-  else
+  }
+  else {
     RegisterPreservingCC = DefaultCC;
+  }
 
   ABITypes = new CodeGenABITypes(clangASTContext, Module);
 

lib/LLVMPasses/ARCEntryPointBuilder.h

@@ -19,6 +19,7 @@
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Module.h"
 #include "llvm/ADT/APInt.h"
+#include "llvm/ADT/Triple.h"
 
 namespace swift {
 
@@ -86,10 +87,26 @@ class ARCEntryPointBuilder {
 public:
   ARCEntryPointBuilder(Function &F)
       : B(&*F.begin()), Retain(), ObjectPtrTy(),
-        DefaultCC(SWIFT_LLVM_CC(DefaultCC)),
-        RegisterPreservingCC(SWIFT_LLVM_CC(RegisterPreservingCC)) {
-    //TODO: If the target does not support the new calling convention,
-    //set RegisterPreservingCC to use a standard C calling convention.
+        DefaultCC(SWIFT_LLVM_CC(DefaultCC)) {
+    //If the target does not support the new calling convention,
+    //set RegisterPreservingCC to use a default calling convention.
+    RegisterPreservingCC = DefaultCC;
+
+    // Check if the register preserving calling convention
+    // is supported by the backend and should be used
+    // for the deployment target provided for this compilation.
+    if (SWIFT_RT_USE_RegisterPreservingCC) {
+      bool ShouldUseRegisterPreservingCC = false;
+      auto &TargeTriple = F.getParent()->getTargetTriple();
+      llvm::Triple Triple(TargeTriple);
+      auto Arch = Triple.getArch();
+      if (Arch == llvm::Triple::ArchType::aarch64) {
+        ShouldUseRegisterPreservingCC = true;
+      }
+
+      if (ShouldUseRegisterPreservingCC)
+        RegisterPreservingCC = SWIFT_LLVM_CC(RegisterPreservingCC);
+    }
   }
 
   ~ARCEntryPointBuilder() = default;