mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-07-28 20:29:21 +00:00
f2286b0152
on a per-callsite walk of the called function's instructions, in breadth-first order over the potentially reachable set of basic blocks. This is a major shift in how inline cost analysis works to improve the accuracy and rationality of inlining decisions. A brief outline of the algorithm this moves to: - Build a simplification mapping based on the callsite arguments to the function arguments. - Push the entry block onto a worklist of potentially-live basic blocks. - Pop the first block off of the *front* of the worklist (for breadth-first ordering) and walk its instructions using a custom InstVisitor. - For each instruction's operands, re-map them based on the simplification mappings available for the given callsite. - Compute any simplification possible of the instruction after re-mapping, and store that back int othe simplification mapping. - Compute any bonuses, costs, or other impacts of the instruction on the cost metric. - When the terminator is reached, replace any conditional value in the terminator with any simplifications from the mapping we have, and add any successors which are not proven to be dead from these simplifications to the worklist. - Pop the next block off of the front of the worklist, and repeat. - As soon as the cost of inlining exceeds the threshold for the callsite, stop analyzing the function in order to bound cost. The primary goal of this algorithm is to perfectly handle dead code paths. We do not want any code in trivially dead code paths to impact inlining decisions. The previous metric was *extremely* flawed here, and would always subtract the average cost of two successors of a conditional branch when it was proven to become an unconditional branch at the callsite. There was no handling of wildly different costs between the two successors, which would cause inlining when the path actually taken was too large, and no inlining when the path actually taken was trivially simple. There was also no handling of the code *path*, only the immediate successors. These problems vanish completely now. See the added regression tests for the shiny new features -- we skip recursive function calls, SROA-killing instructions, and high cost complex CFG structures when dead at the callsite being analyzed. Switching to this algorithm required refactoring the inline cost interface to accept the actual threshold rather than simply returning a single cost. The resulting interface is pretty bad, and I'm planning to do lots of interface cleanup after this patch. Several other refactorings fell out of this, but I've tried to minimize them for this patch. =/ There is still more cleanup that can be done here. Please point out anything that you see in review. I've worked really hard to try to mirror at least the spirit of all of the previous heuristics in the new model. It's not clear that they are all correct any more, but I wanted to minimize the change in this single patch, it's already a bit ridiculous. One heuristic that is *not* yet mirrored is to allow inlining of functions with a dynamic alloca *if* the caller has a dynamic alloca. I will add this back, but I think the most reasonable way requires changes to the inliner itself rather than just the cost metric, and so I've deferred this for a subsequent patch. The test case is XFAIL-ed until then. As mentioned in the review mail, this seems to make Clang run about 1% to 2% faster in -O0, but makes its binary size grow by just under 4%. I've looked into the 4% growth, and it can be fixed, but requires changes to other parts of the inliner. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153812 91177308-0d34-0410-b5e6-96231b3b80d8
94 lines
3.2 KiB
C++
94 lines
3.2 KiB
C++
//===- CodeMetrics.h - Code cost measurements -------------------*- C++ -*-===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file implements various weight measurements for code, helping
|
|
// the Inliner and other passes decide whether to duplicate its contents.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#ifndef LLVM_ANALYSIS_CODEMETRICS_H
|
|
#define LLVM_ANALYSIS_CODEMETRICS_H
|
|
|
|
#include "llvm/ADT/DenseMap.h"
|
|
|
|
namespace llvm {
|
|
class BasicBlock;
|
|
class Function;
|
|
class Instruction;
|
|
class TargetData;
|
|
class Value;
|
|
|
|
/// \brief Check whether an instruction is likely to be "free" when lowered.
|
|
bool isInstructionFree(const Instruction *I, const TargetData *TD = 0);
|
|
|
|
/// \brief Check whether a call will lower to something small.
|
|
///
|
|
/// This tests checks whether calls to this function will lower to something
|
|
/// significantly cheaper than a traditional call, often a single
|
|
/// instruction.
|
|
bool callIsSmall(const Function *F);
|
|
|
|
/// \brief Utility to calculate the size and a few similar metrics for a set
|
|
/// of basic blocks.
|
|
struct CodeMetrics {
|
|
/// \brief True if this function contains a call to setjmp or other functions
|
|
/// with attribute "returns twice" without having the attribute itself.
|
|
bool exposesReturnsTwice;
|
|
|
|
/// \brief True if this function calls itself.
|
|
bool isRecursive;
|
|
|
|
/// \brief True if this function contains one or more indirect branches.
|
|
bool containsIndirectBr;
|
|
|
|
/// \brief True if this function calls alloca (in the C sense).
|
|
bool usesDynamicAlloca;
|
|
|
|
/// \brief Number of instructions in the analyzed blocks.
|
|
unsigned NumInsts;
|
|
|
|
/// \brief Number of analyzed blocks.
|
|
unsigned NumBlocks;
|
|
|
|
/// \brief Keeps track of basic block code size estimates.
|
|
DenseMap<const BasicBlock *, unsigned> NumBBInsts;
|
|
|
|
/// \brief Keep track of the number of calls to 'big' functions.
|
|
unsigned NumCalls;
|
|
|
|
/// \brief The number of calls to internal functions with a single caller.
|
|
///
|
|
/// These are likely targets for future inlining, likely exposed by
|
|
/// interleaved devirtualization.
|
|
unsigned NumInlineCandidates;
|
|
|
|
/// \brief How many instructions produce vector values.
|
|
///
|
|
/// The inliner is more aggressive with inlining vector kernels.
|
|
unsigned NumVectorInsts;
|
|
|
|
/// \brief How many 'ret' instructions the blocks contain.
|
|
unsigned NumRets;
|
|
|
|
CodeMetrics() : exposesReturnsTwice(false), isRecursive(false),
|
|
containsIndirectBr(false), usesDynamicAlloca(false),
|
|
NumInsts(0), NumBlocks(0), NumCalls(0),
|
|
NumInlineCandidates(0), NumVectorInsts(0),
|
|
NumRets(0) {}
|
|
|
|
/// \brief Add information about a block to the current state.
|
|
void analyzeBasicBlock(const BasicBlock *BB, const TargetData *TD = 0);
|
|
|
|
/// \brief Add information about a function to the current state.
|
|
void analyzeFunction(Function *F, const TargetData *TD = 0);
|
|
};
|
|
}
|
|
|
|
#endif
|