x86_64: Fix calls to __morestack under the large code model.

Under the large code model, we cannot assume that __morestack lives within
2^31 bytes of the call site, so we cannot use pc-relative addressing. We
cannot perform the call via a temporary register, as the rax register may
be used to store the static chain, and all other suitable registers may be
either callee-save or used for parameter passing. We cannot use the stack
at this point either because __morestack manipulates the stack directly.

To avoid these issues, perform an indirect call via a read-only memory
location containing the address.

This solution is not perfect, as it assumes that the .rodata section
is laid out within 2^31 bytes of each function body, but this seems to
be sufficient for JIT.

Differential Revision: http://reviews.llvm.org/D6787

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225003 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineModuleInfo.h

@@ -161,6 +161,13 @@ class MachineModuleInfo : public ImmutablePass {
   /// to _fltused on Windows targets.
   bool UsesVAFloatArgument;
 
+  /// UsesMorestackAddr - True if the module calls the __morestack function
+  /// indirectly, as is required under the large code model on x86. This is used
+  /// to emit a definition of a symbol, __morestack_addr, containing the
+  /// address. See comments in lib/Target/X86/X86FrameLowering.cpp for more
+  /// details.
+  bool UsesMorestackAddr;
+
 public:
   static char ID; // Pass identification, replacement for typeid
 
@@ -234,6 +241,14 @@ public:
     UsesVAFloatArgument = b;
   }
 
+  bool usesMorestackAddr() const {
+    return UsesMorestackAddr;
+  }
+
+  void setUsesMorestackAddr(bool b) {
+    UsesMorestackAddr = b;
+  }
+
   /// \brief Returns a reference to a list of cfi instructions in the current
   /// function's prologue.  Used to construct frame maps for debug and exception
   /// handling comsumers.