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 bool llvm::isInstructionFree(const Instruction *I, const TargetData *TD) {
54   if (isa<PHINode>(I))
55     return true;
56 
57   // If a GEP has all constant indices, it will probably be folded with
58   // a load/store.
59   if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I))
60     return GEP->hasAllConstantIndices();
61 
62   if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
63     switch (II->getIntrinsicID()) {
64     default:
65       return false;
66     case Intrinsic::dbg_declare:
67     case Intrinsic::dbg_value:
68     case Intrinsic::invariant_start:
69     case Intrinsic::invariant_end:
70     case Intrinsic::lifetime_start:
71     case Intrinsic::lifetime_end:
72     case Intrinsic::objectsize:
73     case Intrinsic::ptr_annotation:
74     case Intrinsic::var_annotation:
75       // These intrinsics don't count as size.
76       return true;
77     }
78   }
79 
80   if (const CastInst *CI = dyn_cast<CastInst>(I)) {
81     // Noop casts, including ptr <-> int,  don't count.
82     if (CI->isLosslessCast() || isa<IntToPtrInst>(CI) || isa<PtrToIntInst>(CI))
83       return true;
84     // trunc to a native type is free (assuming the target has compare and
85     // shift-right of the same width).
86     if (TD && isa<TruncInst>(CI) &&
87         TD->isLegalInteger(TD->getTypeSizeInBits(CI->getType())))
88       return true;
89     // Result of a cmp instruction is often extended (to be used by other
90     // cmp instructions, logical or return instructions). These are usually
91     // nop on most sane targets.
92     if (isa<CmpInst>(CI->getOperand(0)))
93       return true;
94   }
95 
96   return false;
97 }
98 
99 /// analyzeBasicBlock - Fill in the current structure with information gleaned
100 /// from the specified block.
101 void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
102                                     const TargetData *TD) {
103   ++NumBlocks;
104   unsigned NumInstsBeforeThisBB = NumInsts;
105   for (BasicBlock::const_iterator II = BB->begin(), E = BB->end();
106        II != E; ++II) {
107     if (isInstructionFree(II, TD))
108       continue;
109 
110     // Special handling for calls.
111     if (isa<CallInst>(II) || isa<InvokeInst>(II)) {
112       ImmutableCallSite CS(cast<Instruction>(II));
113 
114       if (const Function *F = CS.getCalledFunction()) {
115         // If a function is both internal and has a single use, then it is
116         // extremely likely to get inlined in the future (it was probably
117         // exposed by an interleaved devirtualization pass).
118         if (!CS.isNoInline() && F->hasInternalLinkage() && F->hasOneUse())
119           ++NumInlineCandidates;
120 
121         // If this call is to function itself, then the function is recursive.
122         // Inlining it into other functions is a bad idea, because this is
123         // basically just a form of loop peeling, and our metrics aren't useful
124         // for that case.
125         if (F == BB->getParent())
126           isRecursive = true;
127       }
128 
129       if (!isa<IntrinsicInst>(II) && !callIsSmall(CS.getCalledFunction())) {
130         // Each argument to a call takes on average one instruction to set up.
131         NumInsts += CS.arg_size();
132 
133         // We don't want inline asm to count as a call - that would prevent loop
134         // unrolling. The argument setup cost is still real, though.
135         if (!isa<InlineAsm>(CS.getCalledValue()))
136           ++NumCalls;
137       }
138     }
139 
140     if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
141       if (!AI->isStaticAlloca())
142         this->usesDynamicAlloca = true;
143     }
144 
145     if (isa<ExtractElementInst>(II) || II->getType()->isVectorTy())
146       ++NumVectorInsts;
147 
148     ++NumInsts;
149   }
150 
151   if (isa<ReturnInst>(BB->getTerminator()))
152     ++NumRets;
153 
154   // We never want to inline functions that contain an indirectbr.  This is
155   // incorrect because all the blockaddress's (in static global initializers
156   // for example) would be referring to the original function, and this indirect
157   // jump would jump from the inlined copy of the function into the original
158   // function which is extremely undefined behavior.
159   // FIXME: This logic isn't really right; we can safely inline functions
160   // with indirectbr's as long as no other function or global references the
161   // blockaddress of a block within the current function.  And as a QOI issue,
162   // if someone is using a blockaddress without an indirectbr, and that
163   // reference somehow ends up in another function or global, we probably
164   // don't want to inline this function.
165   if (isa<IndirectBrInst>(BB->getTerminator()))
166     containsIndirectBr = true;
167 
168   // Remember NumInsts for this BB.
169   NumBBInsts[BB] = NumInsts - NumInstsBeforeThisBB;
170 }
171 
172 void CodeMetrics::analyzeFunction(Function *F, const TargetData *TD) {
173   // If this function contains a call that "returns twice" (e.g., setjmp or
174   // _setjmp) and it isn't marked with "returns twice" itself, never inline it.
175   // This is a hack because we depend on the user marking their local variables
176   // as volatile if they are live across a setjmp call, and they probably
177   // won't do this in callers.
178   exposesReturnsTwice = F->callsFunctionThatReturnsTwice() &&
179     !F->hasFnAttr(Attribute::ReturnsTwice);
180 
181   // Look at the size of the callee.
182   for (Function::const_iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
183     analyzeBasicBlock(&*BB, TD);
184 }
185