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/CodeMetrics.h"
15 #include "llvm/Function.h"
16 #include "llvm/Support/CallSite.h"
17 #include "llvm/IntrinsicInst.h"
18 #include "llvm/Target/TargetData.h"
19 
20 using namespace llvm;
21 
22 /// callIsSmall - If a call is likely to lower to a single target instruction,
23 /// or is otherwise deemed small return true.
24 /// TODO: Perhaps calls like memcpy, strcpy, etc?
25 bool llvm::callIsSmall(const Function *F) {
26   if (!F) return false;
27 
28   if (F->hasLocalLinkage()) return false;
29 
30   if (!F->hasName()) return false;
31 
32   StringRef Name = F->getName();
33 
34   // These will all likely lower to a single selection DAG node.
35   if (Name == "copysign" || Name == "copysignf" || Name == "copysignl" ||
36       Name == "fabs" || Name == "fabsf" || Name == "fabsl" ||
37       Name == "sin" || Name == "sinf" || Name == "sinl" ||
38       Name == "cos" || Name == "cosf" || Name == "cosl" ||
39       Name == "sqrt" || Name == "sqrtf" || Name == "sqrtl" )
40     return true;
41 
42   // These are all likely to be optimized into something smaller.
43   if (Name == "pow" || Name == "powf" || Name == "powl" ||
44       Name == "exp2" || Name == "exp2l" || Name == "exp2f" ||
45       Name == "floor" || Name == "floorf" || Name == "ceil" ||
46       Name == "round" || Name == "ffs" || Name == "ffsl" ||
47       Name == "abs" || Name == "labs" || Name == "llabs")
48     return true;
49 
50   return false;
51 }
52 
53 /// analyzeBasicBlock - Fill in the current structure with information gleaned
54 /// from the specified block.
55 void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
56                                     const TargetData *TD) {
57   ++NumBlocks;
58   unsigned NumInstsBeforeThisBB = NumInsts;
59   for (BasicBlock::const_iterator II = BB->begin(), E = BB->end();
60        II != E; ++II) {
61     if (isa<PHINode>(II)) continue;           // PHI nodes don't count.
62 
63     // Special handling for calls.
64     if (isa<CallInst>(II) || isa<InvokeInst>(II)) {
65       if (const IntrinsicInst *IntrinsicI = dyn_cast<IntrinsicInst>(II)) {
66         switch (IntrinsicI->getIntrinsicID()) {
67         default: break;
68         case Intrinsic::dbg_declare:
69         case Intrinsic::dbg_value:
70         case Intrinsic::invariant_start:
71         case Intrinsic::invariant_end:
72         case Intrinsic::lifetime_start:
73         case Intrinsic::lifetime_end:
74         case Intrinsic::objectsize:
75         case Intrinsic::ptr_annotation:
76         case Intrinsic::var_annotation:
77           // These intrinsics don't count as size.
78           continue;
79         }
80       }
81 
82       ImmutableCallSite CS(cast<Instruction>(II));
83 
84       if (const Function *F = CS.getCalledFunction()) {
85         // If a function is both internal and has a single use, then it is
86         // extremely likely to get inlined in the future (it was probably
87         // exposed by an interleaved devirtualization pass).
88         if (!CS.isNoInline() && F->hasInternalLinkage() && F->hasOneUse())
89           ++NumInlineCandidates;
90 
91         // If this call is to function itself, then the function is recursive.
92         // Inlining it into other functions is a bad idea, because this is
93         // basically just a form of loop peeling, and our metrics aren't useful
94         // for that case.
95         if (F == BB->getParent())
96           isRecursive = true;
97       }
98 
99       if (!isa<IntrinsicInst>(II) && !callIsSmall(CS.getCalledFunction())) {
100         // Each argument to a call takes on average one instruction to set up.
101         NumInsts += CS.arg_size();
102 
103         // We don't want inline asm to count as a call - that would prevent loop
104         // unrolling. The argument setup cost is still real, though.
105         if (!isa<InlineAsm>(CS.getCalledValue()))
106           ++NumCalls;
107       }
108     }
109 
110     if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
111       if (!AI->isStaticAlloca())
112         this->usesDynamicAlloca = true;
113     }
114 
115     if (isa<ExtractElementInst>(II) || II->getType()->isVectorTy())
116       ++NumVectorInsts;
117 
118     if (const CastInst *CI = dyn_cast<CastInst>(II)) {
119       // Noop casts, including ptr <-> int,  don't count.
120       if (CI->isLosslessCast() || isa<IntToPtrInst>(CI) ||
121           isa<PtrToIntInst>(CI))
122         continue;
123       // trunc to a native type is free (assuming the target has compare and
124       // shift-right of the same width).
125       if (isa<TruncInst>(CI) && TD &&
126           TD->isLegalInteger(TD->getTypeSizeInBits(CI->getType())))
127         continue;
128       // Result of a cmp instruction is often extended (to be used by other
129       // cmp instructions, logical or return instructions). These are usually
130       // nop on most sane targets.
131       if (isa<CmpInst>(CI->getOperand(0)))
132         continue;
133     } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(II)){
134       // If a GEP has all constant indices, it will probably be folded with
135       // a load/store.
136       if (GEPI->hasAllConstantIndices())
137         continue;
138     }
139 
140     ++NumInsts;
141   }
142 
143   if (isa<ReturnInst>(BB->getTerminator()))
144     ++NumRets;
145 
146   // We never want to inline functions that contain an indirectbr.  This is
147   // incorrect because all the blockaddress's (in static global initializers
148   // for example) would be referring to the original function, and this indirect
149   // jump would jump from the inlined copy of the function into the original
150   // function which is extremely undefined behavior.
151   // FIXME: This logic isn't really right; we can safely inline functions
152   // with indirectbr's as long as no other function or global references the
153   // blockaddress of a block within the current function.  And as a QOI issue,
154   // if someone is using a blockaddress without an indirectbr, and that
155   // reference somehow ends up in another function or global, we probably
156   // don't want to inline this function.
157   if (isa<IndirectBrInst>(BB->getTerminator()))
158     containsIndirectBr = true;
159 
160   // Remember NumInsts for this BB.
161   NumBBInsts[BB] = NumInsts - NumInstsBeforeThisBB;
162 }
163 
164 void CodeMetrics::analyzeFunction(Function *F, const TargetData *TD) {
165   // If this function contains a call that "returns twice" (e.g., setjmp or
166   // _setjmp) and it isn't marked with "returns twice" itself, never inline it.
167   // This is a hack because we depend on the user marking their local variables
168   // as volatile if they are live across a setjmp call, and they probably
169   // won't do this in callers.
170   exposesReturnsTwice = F->callsFunctionThatReturnsTwice() &&
171     !F->hasFnAttr(Attribute::ReturnsTwice);
172 
173   // Look at the size of the callee.
174   for (Function::const_iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
175     analyzeBasicBlock(&*BB, TD);
176 }
177