[PATCH] Implement MSVC intrinsics for reading from FS and GS segments.

[Peter Collingbourne]

Hi rnk,

http://llvm-reviews.chandlerc.com/D687

Files:
  include/clang/Basic/Builtins.def
  lib/CodeGen/CGBuiltin.cpp
  test/CodeGen/builtin-ms-fsgs.c

Index: include/clang/Basic/Builtins.def
===================================================================
--- include/clang/Basic/Builtins.def
+++ include/clang/Basic/Builtins.def
@@ -670,6 +670,14 @@
 BUILTIN(__assume, "vb", "n")
 BUILTIN(__noop, "v.", "n")
 BUILTIN(__debugbreak, "v", "n")
+BUILTIN(__readfsbyte, "UcULi", "n")
+BUILTIN(__readfsword, "UsULi", "n")
+BUILTIN(__readfsdword, "ULiULi", "n")
+BUILTIN(__readfsqword, "ULLiULi", "n")
+BUILTIN(__readgsbyte, "UcULi", "n")
+BUILTIN(__readgsword, "UsULi", "n")
+BUILTIN(__readgsdword, "ULiULi", "n")
+BUILTIN(__readgsqword, "ULLiULi", "n")
 
 
 // C99 library functions
Index: lib/CodeGen/CGBuiltin.cpp
===================================================================
--- lib/CodeGen/CGBuiltin.cpp
+++ lib/CodeGen/CGBuiltin.cpp
@@ -1412,6 +1412,27 @@
   }
   case Builtin::BI__noop:
     return RValue::get(0);
+
+  case Builtin::BI__readfsbyte:
+  case Builtin::BI__readfsword:
+  case Builtin::BI__readfsdword:
+  case Builtin::BI__readfsqword:
+  case Builtin::BI__readgsbyte:
+  case Builtin::BI__readgsword:
+  case Builtin::BI__readgsdword:
+  case Builtin::BI__readgsqword: {
+    unsigned AddrSpace = (BuiltinID == Builtin::BI__readfsbyte ||
+                          BuiltinID == Builtin::BI__readfsword ||
+                          BuiltinID == Builtin::BI__readfsdword ||
+                          BuiltinID == Builtin::BI__readfsqword) ? 257 : 256;
+    llvm::Type *ResultType = ConvertType(E->getType());
+
+    llvm::Value *Addr = EmitScalarExpr(E->getArg(0));
+    llvm::Type *AddrPtrType = llvm::PointerType::get(ResultType, AddrSpace);
+    llvm::Value *AddrPtr = Builder.CreateIntToPtr(Addr, AddrPtrType);
+
+    return RValue::get(Builder.CreateLoad(AddrPtr));
+  }
   }
 
   // If this is an alias for a lib function (e.g. __builtin_sin), emit
Index: test/CodeGen/builtin-ms-fsgs.c
===================================================================
--- /dev/null
+++ test/CodeGen/builtin-ms-fsgs.c
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -triple i686-pc-win32 -emit-llvm %s -o - | FileCheck %s
+
+unsigned fsint() {
+  // CHECK: @fsint
+  // CHECK: load i32 addrspace(257)* inttoptr (i32 1 to i32 addrspace(257)*)
+  return __readfsdword(1);
+}
+
+unsigned gsint() {
+  // CHECK: @gsint
+  // CHECK: load i32 addrspace(256)* inttoptr (i32 1 to i32 addrspace(256)*)
+  return __readgsdword(1);
+}
+
+unsigned long fslong(unsigned long x) {
+  // CHECK: @fslong
+  // CHECK: inttoptr i32 {{.*}} to i64 addrspace(257)*
+  // CHECK-NEXT: load i64 addrspace(257)*
+  return __readfsqword(x);
+}
+
+unsigned long gslong(unsigned long x) {
+  // CHECK: @gslong
+  // CHECK: inttoptr i32 {{.*}} to i64 addrspace(256)*
+  // CHECK-NEXT: load i64 addrspace(256)*
+  return __readgsqword(x);
+}
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