1 //===- CodeMetrics.cpp - Code cost measurements ---------------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements code cost measurement utilities.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Analysis/AssumptionTracker.h"
15 #include "llvm/Analysis/CodeMetrics.h"
16 #include "llvm/Analysis/LoopInfo.h"
17 #include "llvm/Analysis/TargetTransformInfo.h"
18 #include "llvm/Analysis/ValueTracking.h"
19 #include "llvm/IR/CallSite.h"
20 #include "llvm/IR/DataLayout.h"
21 #include "llvm/IR/Function.h"
22 #include "llvm/IR/IntrinsicInst.h"
23 #include "llvm/Support/Debug.h"
24 
25 #define DEBUG_TYPE "code-metrics"
26 
27 using namespace llvm;
28 
29 static void completeEphemeralValues(SmallVector<const Value *, 16> &WorkSet,
30                                     SmallPtrSetImpl<const Value*> &EphValues) {
31   SmallPtrSet<const Value *, 32> Visited;
32 
33   // Make sure that all of the items in WorkSet are in our EphValues set.
34   EphValues.insert(WorkSet.begin(), WorkSet.end());
35 
36   // Note: We don't speculate PHIs here, so we'll miss instruction chains kept
37   // alive only by ephemeral values.
38 
39   while (!WorkSet.empty()) {
40     const Value *V = WorkSet.pop_back_val();
41     if (!Visited.insert(V))
42       continue;
43 
44     // If all uses of this value are ephemeral, then so is this value.
45     bool FoundNEUse = false;
46     for (const User *I : V->users())
47       if (!EphValues.count(I)) {
48         FoundNEUse = true;
49         break;
50       }
51 
52     if (FoundNEUse)
53       continue;
54 
55     EphValues.insert(V);
56     DEBUG(dbgs() << "Ephemeral Value: " << *V << "\n");
57 
58     if (const User *U = dyn_cast<User>(V))
59       for (const Value *J : U->operands()) {
60         if (isSafeToSpeculativelyExecute(J))
61           WorkSet.push_back(J);
62       }
63   }
64 }
65 
66 // Find all ephemeral values.
67 void CodeMetrics::collectEphemeralValues(const Loop *L, AssumptionTracker *AT,
68                                          SmallPtrSetImpl<const Value*> &EphValues) {
69   SmallVector<const Value *, 16> WorkSet;
70 
71   for (auto &I : AT->assumptions(L->getHeader()->getParent())) {
72     // Filter out call sites outside of the loop so we don't to a function's
73     // worth of work for each of its loops (and, in the common case, ephemeral
74     // values in the loop are likely due to @llvm.assume calls in the loop).
75     if (!L->contains(I->getParent()))
76       continue;
77 
78     WorkSet.push_back(I);
79   }
80 
81   completeEphemeralValues(WorkSet, EphValues);
82 }
83 
84 void CodeMetrics::collectEphemeralValues(const Function *F, AssumptionTracker *AT,
85                                          SmallPtrSetImpl<const Value*> &EphValues) {
86   SmallVector<const Value *, 16> WorkSet;
87 
88   for (auto &I : AT->assumptions(const_cast<Function*>(F)))
89     WorkSet.push_back(I);
90 
91   completeEphemeralValues(WorkSet, EphValues);
92 }
93 
94 /// analyzeBasicBlock - Fill in the current structure with information gleaned
95 /// from the specified block.
96 void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
97                                     const TargetTransformInfo &TTI,
98                                     SmallPtrSetImpl<const Value*> &EphValues) {
99   ++NumBlocks;
100   unsigned NumInstsBeforeThisBB = NumInsts;
101   for (BasicBlock::const_iterator II = BB->begin(), E = BB->end();
102        II != E; ++II) {
103     // Skip ephemeral values.
104     if (EphValues.count(II))
105       continue;
106 
107     // Special handling for calls.
108     if (isa<CallInst>(II) || isa<InvokeInst>(II)) {
109       ImmutableCallSite CS(cast<Instruction>(II));
110 
111       if (const Function *F = CS.getCalledFunction()) {
112         // If a function is both internal and has a single use, then it is
113         // extremely likely to get inlined in the future (it was probably
114         // exposed by an interleaved devirtualization pass).
115         if (!CS.isNoInline() && F->hasInternalLinkage() && F->hasOneUse())
116           ++NumInlineCandidates;
117 
118         // If this call is to function itself, then the function is recursive.
119         // Inlining it into other functions is a bad idea, because this is
120         // basically just a form of loop peeling, and our metrics aren't useful
121         // for that case.
122         if (F == BB->getParent())
123           isRecursive = true;
124 
125         if (TTI.isLoweredToCall(F))
126           ++NumCalls;
127       } else {
128         // We don't want inline asm to count as a call - that would prevent loop
129         // unrolling. The argument setup cost is still real, though.
130         if (!isa<InlineAsm>(CS.getCalledValue()))
131           ++NumCalls;
132       }
133     }
134 
135     if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
136       if (!AI->isStaticAlloca())
137         this->usesDynamicAlloca = true;
138     }
139 
140     if (isa<ExtractElementInst>(II) || II->getType()->isVectorTy())
141       ++NumVectorInsts;
142 
143     if (const CallInst *CI = dyn_cast<CallInst>(II))
144       if (CI->cannotDuplicate())
145         notDuplicatable = true;
146 
147     if (const InvokeInst *InvI = dyn_cast<InvokeInst>(II))
148       if (InvI->cannotDuplicate())
149         notDuplicatable = true;
150 
151     NumInsts += TTI.getUserCost(&*II);
152   }
153 
154   if (isa<ReturnInst>(BB->getTerminator()))
155     ++NumRets;
156 
157   // We never want to inline functions that contain an indirectbr.  This is
158   // incorrect because all the blockaddress's (in static global initializers
159   // for example) would be referring to the original function, and this indirect
160   // jump would jump from the inlined copy of the function into the original
161   // function which is extremely undefined behavior.
162   // FIXME: This logic isn't really right; we can safely inline functions
163   // with indirectbr's as long as no other function or global references the
164   // blockaddress of a block within the current function.  And as a QOI issue,
165   // if someone is using a blockaddress without an indirectbr, and that
166   // reference somehow ends up in another function or global, we probably
167   // don't want to inline this function.
168   notDuplicatable |= isa<IndirectBrInst>(BB->getTerminator());
169 
170   // Remember NumInsts for this BB.
171   NumBBInsts[BB] = NumInsts - NumInstsBeforeThisBB;
172 }
173