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, 17 insertions, 0 deletions

diff --git a/llvm/lib/IR/Function.cpp b/llvm/lib/IR/Function.cpp
index f9f33fef452..e1b4d4af457 100644
--- a/llvm/lib/IR/Function.cpp
+++ b/llvm/lib/IR/Function.cpp
@@ -1274,3 +1274,20 @@ Optional<uint64_t> Function::getEntryCount() const {
       }
   return None;
 }
+
+void Function::setSectionPrefix(StringRef Prefix) {
+  MDBuilder MDB(getContext());
+  setMetadata(LLVMContext::MD_section_prefix,
+              MDB.createFunctionSectionPrefix(Prefix));
+}
+
+Optional<StringRef> Function::getSectionPrefix() const {
+  if (MDNode *MD = getMetadata(LLVMContext::MD_section_prefix)) {
+    assert(dyn_cast<MDString>(MD->getOperand(0))
+               ->getString()
+               .equals("function_section_prefix") &&
+           "Metadata not match");
+    return dyn_cast<MDString>(MD->getOperand(1))->getString();
+  }
+  return None;
+}