[llvm-exegesis] Add loop mode for repeating the snippet.
Summary:
Before this change the Executable function was made by duplicating the
snippet. This change adds a --repetion-mode={loop|duplicate} flag that
allows choosing between this behaviour and wrapping the snippet instructions
in a loop.
The new mode can help measurements when the snippet fits in the DSB by
short-cirtcuiting decoding. The loop adds a dec + jmp to the measurements, but
since these are not part of the critical path, they execute in parallel
with the measured code and do not impact measurements in practice.
Overview of the change:
- New SnippetRepetitor abstraction that handles repeating the snippet.
The assembler delegates repeating the instructions to this class.
- ExegesisTarget learns how to decrement loop counter and jump.
- Some refactoring of the assembler into FunctionFiller/BasicBlockFiller.
Reviewers: gchatelet
Subscribers: mgorny, tschuett, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68125
llvm-svn: 373083
diff --git a/llvm/tools/llvm-exegesis/lib/Assembler.h b/llvm/tools/llvm-exegesis/lib/Assembler.h
index ff1e8db..5937de9 100644
--- a/llvm/tools/llvm-exegesis/lib/Assembler.h
+++ b/llvm/tools/llvm-exegesis/lib/Assembler.h
@@ -40,6 +40,49 @@
// convention and target machine).
llvm::BitVector getFunctionReservedRegs(const llvm::TargetMachine &TM);
+// Helper to fill in a basic block.
+class BasicBlockFiller {
+public:
+ BasicBlockFiller(MachineFunction &MF, MachineBasicBlock *MBB,
+ const MCInstrInfo *MCII);
+
+ void addInstruction(const MCInst &Inst, const DebugLoc &DL = DebugLoc());
+ void addInstructions(ArrayRef<llvm::MCInst> Insts,
+ const DebugLoc &DL = DebugLoc());
+
+ void addReturn(const DebugLoc &DL = DebugLoc());
+
+ MachineFunction &MF;
+ MachineBasicBlock *const MBB;
+ const MCInstrInfo *const MCII;
+};
+
+// Helper to fill in a function.
+class FunctionFiller {
+public:
+ FunctionFiller(MachineFunction &MF, std::vector<unsigned> RegistersSetUp);
+
+ // Adds a basic block to the function.
+ BasicBlockFiller addBasicBlock();
+
+ // Returns the function entry point.
+ BasicBlockFiller getEntry() { return Entry; }
+
+ MachineFunction &MF;
+ const MCInstrInfo *const MCII;
+
+ // Returns the set of registers in the snippet setup code.
+ ArrayRef<unsigned> getRegistersSetUp() const;
+
+private:
+ BasicBlockFiller Entry;
+ // The set of registers that are set up in the basic block.
+ std::vector<unsigned> RegistersSetUp;
+};
+
+// A callback that fills a function.
+using FillFunction = std::function<void(FunctionFiller &)>;
+
// Creates a temporary `void foo(char*)` function containing the provided
// Instructions. Runs a set of llvm Passes to provide correct prologue and
// epilogue. Once the MachineFunction is ready, it is assembled for TM to
@@ -48,7 +91,7 @@
std::unique_ptr<llvm::LLVMTargetMachine> TM,
llvm::ArrayRef<unsigned> LiveIns,
llvm::ArrayRef<RegisterValue> RegisterInitialValues,
- llvm::ArrayRef<llvm::MCInst> Instructions,
+ const FillFunction &Fill,
llvm::raw_pwrite_stream &AsmStream);
// Creates an ObjectFile in the format understood by the host.
@@ -81,6 +124,12 @@
llvm::StringRef FunctionBytes;
};
+// Creates a void(int8*) MachineFunction.
+llvm::MachineFunction &
+createVoidVoidPtrMachineFunction(llvm::StringRef FunctionID,
+ llvm::Module *Module,
+ llvm::MachineModuleInfo *MMI);
+
} // namespace exegesis
} // namespace llvm