Use profile info to set function section prefix to group hot/cold functions.

Summary:
The original implementation is in r261607, which was reverted in r269726 to accomendate the ProfileSummaryInfo analysis pass. The new implementation:
1. add a new metadata for function section prefix
2. query against ProfileSummaryInfo in CGP to set the correct section prefix for each function
3. output the section prefix set by CGP

Reviewers: davidxl, eraman

Subscribers: vsk, llvm-commits

Differential Revision: https://reviews.llvm.org/D24989

llvm-svn: 284533

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/IR/MDBuilder.cpp b/llvm/lib/IR/MDBuilder.cpp
index a5a4cd06db0..f4bfd599215 100644
--- a/llvm/lib/IR/MDBuilder.cpp
+++ b/llvm/lib/IR/MDBuilder.cpp
@@ -63,6 +63,12 @@ MDNode *MDBuilder::createFunctionEntryCount(uint64_t Count) {
                       createConstant(ConstantInt::get(Int64Ty, Count))});
 }
 
+MDNode *MDBuilder::createFunctionSectionPrefix(StringRef Prefix) {
+  return MDNode::get(Context,
+                     {createString("function_section_prefix"),
+                      createString(Prefix)});
+}
+
 MDNode *MDBuilder::createRange(const APInt &Lo, const APInt &Hi) {
   assert(Lo.getBitWidth() == Hi.getBitWidth() && "Mismatched bitwidths!");