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This adds a set of utility functions for collecting 'ephemeral' values. These are LLVM IR values that are used only by @llvm.assume intrinsics (directly or indirectly), and thus will be removed prior to code generation, implying that they should be considered free for certain purposes (like inlining). The inliner's cost analysis, and a few other passes, have been updated to account for ephemeral values using the provided functionality. This functionality is important for the usability of @llvm.assume, because it limits the "non-local" side-effects of adding llvm.assume on inlining, loop unrolling, etc. (these are hints, and do not generate code, so they should not directly contribute to estimates of execution cost). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217335 91177308-0d34-0410-b5e6-96231b3b80d8
144 lines
4.8 KiB
C++
144 lines
4.8 KiB
C++
//===- InlineCost.h - Cost analysis for inliner -----------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements heuristics for inlining decisions.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_INLINECOST_H
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#define LLVM_ANALYSIS_INLINECOST_H
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#include "llvm/Analysis/CallGraphSCCPass.h"
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#include <cassert>
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#include <climits>
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namespace llvm {
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class AssumptionTracker;
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class CallSite;
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class DataLayout;
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class Function;
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class TargetTransformInfo;
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namespace InlineConstants {
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// Various magic constants used to adjust heuristics.
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const int InstrCost = 5;
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const int IndirectCallThreshold = 100;
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const int CallPenalty = 25;
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const int LastCallToStaticBonus = -15000;
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const int ColdccPenalty = 2000;
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const int NoreturnPenalty = 10000;
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/// Do not inline functions which allocate this many bytes on the stack
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/// when the caller is recursive.
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const unsigned TotalAllocaSizeRecursiveCaller = 1024;
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}
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/// \brief Represents the cost of inlining a function.
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///
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/// This supports special values for functions which should "always" or
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/// "never" be inlined. Otherwise, the cost represents a unitless amount;
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/// smaller values increase the likelihood of the function being inlined.
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///
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/// Objects of this type also provide the adjusted threshold for inlining
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/// based on the information available for a particular callsite. They can be
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/// directly tested to determine if inlining should occur given the cost and
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/// threshold for this cost metric.
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class InlineCost {
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enum SentinelValues {
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AlwaysInlineCost = INT_MIN,
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NeverInlineCost = INT_MAX
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};
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/// \brief The estimated cost of inlining this callsite.
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const int Cost;
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/// \brief The adjusted threshold against which this cost was computed.
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const int Threshold;
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// Trivial constructor, interesting logic in the factory functions below.
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InlineCost(int Cost, int Threshold) : Cost(Cost), Threshold(Threshold) {}
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public:
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static InlineCost get(int Cost, int Threshold) {
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assert(Cost > AlwaysInlineCost && "Cost crosses sentinel value");
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assert(Cost < NeverInlineCost && "Cost crosses sentinel value");
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return InlineCost(Cost, Threshold);
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}
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static InlineCost getAlways() {
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return InlineCost(AlwaysInlineCost, 0);
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}
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static InlineCost getNever() {
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return InlineCost(NeverInlineCost, 0);
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}
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/// \brief Test whether the inline cost is low enough for inlining.
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LLVM_EXPLICIT operator bool() const {
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return Cost < Threshold;
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}
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bool isAlways() const { return Cost == AlwaysInlineCost; }
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bool isNever() const { return Cost == NeverInlineCost; }
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bool isVariable() const { return !isAlways() && !isNever(); }
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/// \brief Get the inline cost estimate.
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/// It is an error to call this on an "always" or "never" InlineCost.
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int getCost() const {
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assert(isVariable() && "Invalid access of InlineCost");
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return Cost;
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}
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/// \brief Get the cost delta from the threshold for inlining.
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/// Only valid if the cost is of the variable kind. Returns a negative
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/// value if the cost is too high to inline.
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int getCostDelta() const { return Threshold - getCost(); }
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};
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/// \brief Cost analyzer used by inliner.
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class InlineCostAnalysis : public CallGraphSCCPass {
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const TargetTransformInfo *TTI;
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AssumptionTracker *AT;
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public:
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static char ID;
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InlineCostAnalysis();
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~InlineCostAnalysis();
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// Pass interface implementation.
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void getAnalysisUsage(AnalysisUsage &AU) const override;
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bool runOnSCC(CallGraphSCC &SCC) override;
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/// \brief Get an InlineCost object representing the cost of inlining this
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/// callsite.
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///
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/// Note that threshold is passed into this function. Only costs below the
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/// threshold are computed with any accuracy. The threshold can be used to
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/// bound the computation necessary to determine whether the cost is
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/// sufficiently low to warrant inlining.
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///
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/// Also note that calling this function *dynamically* computes the cost of
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/// inlining the callsite. It is an expensive, heavyweight call.
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InlineCost getInlineCost(CallSite CS, int Threshold);
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/// \brief Get an InlineCost with the callee explicitly specified.
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/// This allows you to calculate the cost of inlining a function via a
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/// pointer. This behaves exactly as the version with no explicit callee
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/// parameter in all other respects.
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//
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// Note: This is used by out-of-tree passes, please do not remove without
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// adding a replacement API.
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InlineCost getInlineCost(CallSite CS, Function *Callee, int Threshold);
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/// \brief Minimal filter to detect invalid constructs for inlining.
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bool isInlineViable(Function &Callee);
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};
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}
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#endif
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