[X86] Introduce a large data threshold for the medium code model

Currently clang's medium code model treats all data as large, putting them in a large data section and using more expensive instruction sequences to access them.

Following gcc's -mlarge-data-threshold, which allows putting data under a certain size in a normal data section as opposed to a large data section. This allows using cheaper code sequences to access some portion of data in the binary (which will be implemented in LLVM in a future patch).

And under the medium codel mode, only put data above the large data threshold into large data sections, not all data.

Reviewed By: MaskRay, rnk

Differential Revision: https://reviews.llvm.org/D149288

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/CommandFlags.cpp b/llvm/lib/CodeGen/CommandFlags.cpp
index 59bd6da..1eba979 100644
--- a/llvm/lib/CodeGen/CommandFlags.cpp
+++ b/llvm/lib/CodeGen/CommandFlags.cpp
@@ -58,6 +58,7 @@ CGLIST(std::string, MAttrs)
 CGOPT_EXP(Reloc::Model, RelocModel)
 CGOPT(ThreadModel::Model, ThreadModel)
 CGOPT_EXP(CodeModel::Model, CodeModel)
+CGOPT_EXP(uint64_t, LargeDataThreshold)
 CGOPT(ExceptionHandling, ExceptionModel)
 CGOPT_EXP(CodeGenFileType, FileType)
 CGOPT(FramePointerKind, FramePointerUsage)
@@ -162,6 +163,12 @@ codegen::RegisterCodeGenFlags::RegisterCodeGenFlags() {
                  clEnumValN(CodeModel::Large, "large", "Large code model")));
   CGBINDOPT(CodeModel);
 
+  static cl::opt<uint64_t> LargeDataThreshold(
+      "large-data-threshold",
+      cl::desc("Choose large data threshold for x86_64 medium code model"),
+      cl::init(0));
+  CGBINDOPT(LargeDataThreshold);
+
   static cl::opt<ExceptionHandling> ExceptionModel(
       "exception-model", cl::desc("exception model"),
       cl::init(ExceptionHandling::None),