[PATCH] Add function entry count metadata.
Justin Bogner
mail at justinbogner.com
Fri May 8 16:15:09 PDT 2015
Diego Novillo <dnovillo at google.com> writes:
> Hi dexonsmith, bogner,
>
> This adds three Function methods to handle function entry counts:
> setEntryCount(), hasEntryCount() and getEntryCount().
>
> Entry counts are stored under the MD_prof metadata node with the name
> "function_entry_count". They are unsigned 64 bit values set by profilers
> (instrumentation and sample profiler changes coming up).
>
> I had some internal debate about what to return when
> Function::getEntryCount() is called without the function having its
> metadata set. I don't want to return a special sentinel value, because
> those are typically problematic down the road.
>
> So, I added a Function::hasEntryCount() predicate. If
> Function::getEntryCount() is called with no metadata present, it will
> cause a compiler assertion.
How about returning an Optional<uint64_t>? It should be about the same
for the caller and it's harder to misuse, ie, instead of:
if (Fn.hasEntryCount())
doStuffWith(Fn.getEntryCount())
We'd get:
if (auto C = Fn.getEntryCount())
doStuffWith(*C)
> http://reviews.llvm.org/D9628
>
> Files:
> include/llvm/IR/Function.h
> include/llvm/IR/MDBuilder.h
> lib/IR/MDBuilder.cpp
> unittests/IR/MetadataTest.cpp
>
> Index: include/llvm/IR/Function.h
> ===================================================================
> --- include/llvm/IR/Function.h
> +++ include/llvm/IR/Function.h
> @@ -23,7 +23,11 @@
> #include "llvm/IR/Attributes.h"
> #include "llvm/IR/BasicBlock.h"
> #include "llvm/IR/CallingConv.h"
> +#include "llvm/IR/Constants.h"
> #include "llvm/IR/GlobalObject.h"
> +#include "llvm/IR/LLVMContext.h"
> +#include "llvm/IR/MDBuilder.h"
> +#include "llvm/IR/Metadata.h"
> #include "llvm/Support/Compiler.h"
>
> namespace llvm {
> @@ -194,6 +198,29 @@
> AttributeSet::FunctionIndex, Kind, Value));
> }
>
> + /// @brief Set the entry count for this function.
> + void setEntryCount(uint64_t Count) {
> + MDBuilder MDB(getContext());
> + setMetadata(LLVMContext::MD_prof, MDB.createFunctionEntryCount(Count));
> + }
> +
> + /// @brief Return true if the function has a known entry count.
> + bool hasEntryCount() const {
> + MDNode *MD = getMetadata(LLVMContext::MD_prof);
> + if (MD && MD->getOperand(0))
> + if (MDString* MDS = dyn_cast<MDString>(MD->getOperand(0)))
> + return MDS->getString().equals("function_entry_count");
> + return false;
> + }
> +
> + /// @brief Get the entry count for this function.
> + uint64_t getEntryCount() const {
> + assert(hasEntryCount() && "No entry count available for this function");
> + MDNode *MD = getMetadata(LLVMContext::MD_prof);
> + ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(1));
> + return CI->getValue().getZExtValue();
> + }
> +
> /// @brief Return true if the function has the attribute.
> bool hasFnAttribute(Attribute::AttrKind Kind) const {
> return AttributeSets.hasAttribute(AttributeSet::FunctionIndex, Kind);
> Index: include/llvm/IR/MDBuilder.h
> ===================================================================
> --- include/llvm/IR/MDBuilder.h
> +++ include/llvm/IR/MDBuilder.h
> @@ -60,6 +60,9 @@
> /// \brief Return metadata containing a number of branch weights.
> MDNode *createBranchWeights(ArrayRef<uint32_t> Weights);
>
> + /// \brief Return metadata containing the entry count for a function.
> + MDNode *createFunctionEntryCount(uint64_t Count);
> +
> //===------------------------------------------------------------------===//
> // Range metadata.
> //===------------------------------------------------------------------===//
> Index: lib/IR/MDBuilder.cpp
> ===================================================================
> --- lib/IR/MDBuilder.cpp
> +++ lib/IR/MDBuilder.cpp
> @@ -53,6 +53,16 @@
> return MDNode::get(Context, Vals);
> }
>
> +MDNode *MDBuilder::createFunctionEntryCount(uint64_t Count) {
> + SmallVector<Metadata *, 2> Vals(2);
> + Vals[0] = createString("function_entry_count");
> +
> + Type *Int64Ty = Type::getInt64Ty(Context);
> + Vals[1] = createConstant(ConstantInt::get(Int64Ty, Count));
> +
> + return MDNode::get(Context, Vals);
> +}
> +
> MDNode *MDBuilder::createRange(const APInt &Lo, const APInt &Hi) {
> assert(Lo.getBitWidth() == Hi.getBitWidth() && "Mismatched bitwidths!");
>
> Index: unittests/IR/MetadataTest.cpp
> ===================================================================
> --- unittests/IR/MetadataTest.cpp
> +++ unittests/IR/MetadataTest.cpp
> @@ -2272,4 +2272,12 @@
> EXPECT_FALSE(verifyFunction(*F));
> }
>
> +TEST_F(FunctionAttachmentTest, EntryCount) {
> + Function *F = getFunction("foo");
> + EXPECT_FALSE(F->hasEntryCount());
> + F->setEntryCount(12304);
> + EXPECT_TRUE(F->hasEntryCount());
> + EXPECT_EQ(12304u, F->getEntryCount());
> +}
> +
> }
>
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