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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
100 lines
3.7 KiB
C++
100 lines
3.7 KiB
C++
//===- InlinerPass.h - Code common to all inliners --------------*- 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 defines a simple policy-based bottom-up inliner. This file
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// implements all of the boring mechanics of the bottom-up inlining, while the
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// subclass determines WHAT to inline, which is the much more interesting
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// component.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TRANSFORMS_IPO_INLINERPASS_H
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#define LLVM_TRANSFORMS_IPO_INLINERPASS_H
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#include "llvm/CallGraphSCCPass.h"
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namespace llvm {
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class CallSite;
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class TargetData;
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class InlineCost;
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template<class PtrType, unsigned SmallSize>
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class SmallPtrSet;
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/// Inliner - This class contains all of the helper code which is used to
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/// perform the inlining operations that do not depend on the policy.
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///
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struct Inliner : public CallGraphSCCPass {
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explicit Inliner(char &ID);
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explicit Inliner(char &ID, int Threshold, bool InsertLifetime);
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/// getAnalysisUsage - For this class, we declare that we require and preserve
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/// the call graph. If the derived class implements this method, it should
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/// always explicitly call the implementation here.
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virtual void getAnalysisUsage(AnalysisUsage &Info) const;
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// Main run interface method, this implements the interface required by the
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// Pass class.
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virtual bool runOnSCC(CallGraphSCC &SCC);
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// doFinalization - Remove now-dead linkonce functions at the end of
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// processing to avoid breaking the SCC traversal.
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virtual bool doFinalization(CallGraph &CG);
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/// This method returns the value specified by the -inline-threshold value,
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/// specified on the command line. This is typically not directly needed.
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///
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unsigned getInlineThreshold() const { return InlineThreshold; }
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/// Calculate the inline threshold for given Caller. This threshold is lower
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/// if the caller is marked with OptimizeForSize and -inline-threshold is not
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/// given on the comand line. It is higher if the callee is marked with the
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/// inlinehint attribute.
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///
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unsigned getInlineThreshold(CallSite CS) const;
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/// getInlineCost - This method must be implemented by the subclass to
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/// determine the cost of inlining the specified call site. If the cost
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/// returned is greater than the current inline threshold, the call site is
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/// not inlined.
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///
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virtual InlineCost getInlineCost(CallSite CS) = 0;
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/// resetCachedCostInfo - erase any cached cost data from the derived class.
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/// If the derived class has no such data this can be empty.
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///
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virtual void resetCachedCostInfo(Function* Caller) = 0;
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/// growCachedCostInfo - update the cached cost info for Caller after Callee
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/// has been inlined.
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virtual void growCachedCostInfo(Function *Caller, Function *Callee) = 0;
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/// removeDeadFunctions - Remove dead functions.
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///
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/// This also includes a hack in the form of the 'AlwaysInlineOnly' flag
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/// which restricts it to deleting functions with an 'AlwaysInline'
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/// attribute. This is useful for the InlineAlways pass that only wants to
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/// deal with that subset of the functions.
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bool removeDeadFunctions(CallGraph &CG, bool AlwaysInlineOnly = false);
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private:
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// InlineThreshold - Cache the value here for easy access.
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unsigned InlineThreshold;
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// InsertLifetime - Insert @llvm.lifetime intrinsics.
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bool InsertLifetime;
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/// shouldInline - Return true if the inliner should attempt to
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/// inline at the given CallSite.
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bool shouldInline(CallSite CS);
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};
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} // End llvm namespace
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#endif
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