[PGO] Turn off comdat renaming in IR PGO by default
Summary:
In IR PGO we append the function hash to comdat functions to avoid the
potential hash mismatch. This turns out not legal in some cases: if the comdat
function is address-taken and used in comparison. Renaming changes the semantic.
This patch turns off comdat renaming by default.
To alleviate the hash mismatch issue, we now rename the profile variable
for comdat functions. Profile allows co-existing multiple versions of profiles
with different hash value. The inlined copy will always has the correct profile
counter. The out-of-line copy might not have the correct count. But we will
not have the bogus mismatch warning.
Reviewers: davidxl
Subscribers: llvm-commits, xur
Differential Revision: https://reviews.llvm.org/D28416
llvm-svn: 291588
diff --git a/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp b/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
index 8da3e31..adea7e7 100644
--- a/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
+++ b/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
@@ -32,6 +32,11 @@
cl::desc("Enable name string compression"),
cl::init(true));
+cl::opt<bool> DoHashBasedCounterSplit(
+ "hash-based-counter-split",
+ cl::desc("Rename counter variable of a comdat function based on cfg hash"),
+ cl::init(true));
+
cl::opt<bool> ValueProfileStaticAlloc(
"vp-static-alloc",
cl::desc("Do static counter allocation for value profiler"),
@@ -272,7 +277,16 @@
static std::string getVarName(InstrProfIncrementInst *Inc, StringRef Prefix) {
StringRef NamePrefix = getInstrProfNameVarPrefix();
StringRef Name = Inc->getName()->getName().substr(NamePrefix.size());
- return (Prefix + Name).str();
+ Function *F = Inc->getParent()->getParent();
+ Module *M = F->getParent();
+ if (!DoHashBasedCounterSplit || !isIRPGOFlagSet(M) ||
+ !canRenameComdatFunc(*F))
+ return (Prefix + Name).str();
+ uint64_t FuncHash = Inc->getHash()->getZExtValue();
+ SmallVector<char, 24> HashPostfix;
+ if (Name.endswith((Twine(".") + Twine(FuncHash)).toStringRef(HashPostfix)))
+ return (Prefix + Name).str();
+ return (Prefix + Name + "." + Twine(FuncHash)).str();
}
static inline bool shouldRecordFunctionAddr(Function *F) {