[PM/CC1] Add -f[no-]split-cold-code CC1 option to toggle splitting

This patch adds -f[no-]split-cold-code CC1 options to clang. This allows
the splitting pass to be toggled on/off. The current method of passing
`-mllvm -hot-cold-split=true` to clang isn't ideal as it may not compose
correctly (say, with `-O0` or `-Oz`).

To implement the -fsplit-cold-code option, an attribute is applied to
functions to indicate that they may be considered for splitting. This
removes some complexity from the old/new PM pipeline builders, and
behaves as expected when LTO is enabled.

Co-authored by: Saleem Abdulrasool <compnerd@compnerd.org>
Differential Revision: https://reviews.llvm.org/D57265
Reviewed By: Aditya Kumar, Vedant Kumar
Reviewers: Teresa Johnson, Aditya Kumar, Fedor Sergeev, Philip Pfaffe, Vedant Kumar

1 files changed, 4 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 93b49ec..d577dc7 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -63,6 +63,7 @@
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MD5.h"
 #include "llvm/Support/TimeProfiler.h"
+#include "llvm/Transforms/IPO/HotColdSplitting.h"
 
 using namespace clang;
 using namespace CodeGen;
@@ -1695,6 +1696,9 @@ void CodeGenModule::SetLLVMFunctionAttributesForDefinition(const Decl *D,
 
     if (D->hasAttr<MinSizeAttr>())
       B.addAttribute(llvm::Attribute::MinSize);
+
+    if (CodeGenOpts.SplitColdCode)
+      B.addAttribute(llvm::getHotColdSplittingAttrKind());
   }
 
   F->addAttributes(llvm::AttributeList::FunctionIndex, B);