CodeMetrics.cpp revision 239462
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
20using 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?
25bool llvm::callIsSmall(ImmutableCallSite CS) {
26  if (isa<IntrinsicInst>(CS.getInstruction()))
27    return true;
28
29  const Function *F = CS.getCalledFunction();
30  if (!F) return false;
31
32  if (F->hasLocalLinkage()) return false;
33
34  if (!F->hasName()) return false;
35
36  StringRef Name = F->getName();
37
38  // These will all likely lower to a single selection DAG node.
39  if (Name == "copysign" || Name == "copysignf" || Name == "copysignl" ||
40      Name == "fabs" || Name == "fabsf" || Name == "fabsl" ||
41      Name == "sin" || Name == "sinf" || Name == "sinl" ||
42      Name == "cos" || Name == "cosf" || Name == "cosl" ||
43      Name == "sqrt" || Name == "sqrtf" || Name == "sqrtl" )
44    return true;
45
46  // These are all likely to be optimized into something smaller.
47  if (Name == "pow" || Name == "powf" || Name == "powl" ||
48      Name == "exp2" || Name == "exp2l" || Name == "exp2f" ||
49      Name == "floor" || Name == "floorf" || Name == "ceil" ||
50      Name == "round" || Name == "ffs" || Name == "ffsl" ||
51      Name == "abs" || Name == "labs" || Name == "llabs")
52    return true;
53
54  return false;
55}
56
57bool llvm::isInstructionFree(const Instruction *I, const TargetData *TD) {
58  if (isa<PHINode>(I))
59    return true;
60
61  // If a GEP has all constant indices, it will probably be folded with
62  // a load/store.
63  if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I))
64    return GEP->hasAllConstantIndices();
65
66  if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
67    switch (II->getIntrinsicID()) {
68    default:
69      return false;
70    case Intrinsic::dbg_declare:
71    case Intrinsic::dbg_value:
72    case Intrinsic::invariant_start:
73    case Intrinsic::invariant_end:
74    case Intrinsic::lifetime_start:
75    case Intrinsic::lifetime_end:
76    case Intrinsic::objectsize:
77    case Intrinsic::ptr_annotation:
78    case Intrinsic::var_annotation:
79      // These intrinsics don't count as size.
80      return true;
81    }
82  }
83
84  if (const CastInst *CI = dyn_cast<CastInst>(I)) {
85    // Noop casts, including ptr <-> int,  don't count.
86    if (CI->isLosslessCast())
87      return true;
88
89    Value *Op = CI->getOperand(0);
90    // An inttoptr cast is free so long as the input is a legal integer type
91    // which doesn't contain values outside the range of a pointer.
92    if (isa<IntToPtrInst>(CI) && TD &&
93        TD->isLegalInteger(Op->getType()->getScalarSizeInBits()) &&
94        Op->getType()->getScalarSizeInBits() <= TD->getPointerSizeInBits())
95      return true;
96
97    // A ptrtoint cast is free so long as the result is large enough to store
98    // the pointer, and a legal integer type.
99    if (isa<PtrToIntInst>(CI) && TD &&
100        TD->isLegalInteger(Op->getType()->getScalarSizeInBits()) &&
101        Op->getType()->getScalarSizeInBits() >= TD->getPointerSizeInBits())
102      return true;
103
104    // trunc to a native type is free (assuming the target has compare and
105    // shift-right of the same width).
106    if (TD && isa<TruncInst>(CI) &&
107        TD->isLegalInteger(TD->getTypeSizeInBits(CI->getType())))
108      return true;
109    // Result of a cmp instruction is often extended (to be used by other
110    // cmp instructions, logical or return instructions). These are usually
111    // nop on most sane targets.
112    if (isa<CmpInst>(CI->getOperand(0)))
113      return true;
114  }
115
116  return false;
117}
118
119/// analyzeBasicBlock - Fill in the current structure with information gleaned
120/// from the specified block.
121void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
122                                    const TargetData *TD) {
123  ++NumBlocks;
124  unsigned NumInstsBeforeThisBB = NumInsts;
125  for (BasicBlock::const_iterator II = BB->begin(), E = BB->end();
126       II != E; ++II) {
127    if (isInstructionFree(II, TD))
128      continue;
129
130    // Special handling for calls.
131    if (isa<CallInst>(II) || isa<InvokeInst>(II)) {
132      ImmutableCallSite CS(cast<Instruction>(II));
133
134      if (const Function *F = CS.getCalledFunction()) {
135        // If a function is both internal and has a single use, then it is
136        // extremely likely to get inlined in the future (it was probably
137        // exposed by an interleaved devirtualization pass).
138        if (!CS.isNoInline() && F->hasInternalLinkage() && F->hasOneUse())
139          ++NumInlineCandidates;
140
141        // If this call is to function itself, then the function is recursive.
142        // Inlining it into other functions is a bad idea, because this is
143        // basically just a form of loop peeling, and our metrics aren't useful
144        // for that case.
145        if (F == BB->getParent())
146          isRecursive = true;
147      }
148
149      if (!callIsSmall(CS)) {
150        // Each argument to a call takes on average one instruction to set up.
151        NumInsts += CS.arg_size();
152
153        // We don't want inline asm to count as a call - that would prevent loop
154        // unrolling. The argument setup cost is still real, though.
155        if (!isa<InlineAsm>(CS.getCalledValue()))
156          ++NumCalls;
157      }
158    }
159
160    if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
161      if (!AI->isStaticAlloca())
162        this->usesDynamicAlloca = true;
163    }
164
165    if (isa<ExtractElementInst>(II) || II->getType()->isVectorTy())
166      ++NumVectorInsts;
167
168    ++NumInsts;
169  }
170
171  if (isa<ReturnInst>(BB->getTerminator()))
172    ++NumRets;
173
174  // We never want to inline functions that contain an indirectbr.  This is
175  // incorrect because all the blockaddress's (in static global initializers
176  // for example) would be referring to the original function, and this indirect
177  // jump would jump from the inlined copy of the function into the original
178  // function which is extremely undefined behavior.
179  // FIXME: This logic isn't really right; we can safely inline functions
180  // with indirectbr's as long as no other function or global references the
181  // blockaddress of a block within the current function.  And as a QOI issue,
182  // if someone is using a blockaddress without an indirectbr, and that
183  // reference somehow ends up in another function or global, we probably
184  // don't want to inline this function.
185  if (isa<IndirectBrInst>(BB->getTerminator()))
186    containsIndirectBr = true;
187
188  // Remember NumInsts for this BB.
189  NumBBInsts[BB] = NumInsts - NumInstsBeforeThisBB;
190}
191
192void CodeMetrics::analyzeFunction(Function *F, const TargetData *TD) {
193  // If this function contains a call that "returns twice" (e.g., setjmp or
194  // _setjmp) and it isn't marked with "returns twice" itself, never inline it.
195  // This is a hack because we depend on the user marking their local variables
196  // as volatile if they are live across a setjmp call, and they probably
197  // won't do this in callers.
198  exposesReturnsTwice = F->callsFunctionThatReturnsTwice() &&
199    !F->hasFnAttr(Attribute::ReturnsTwice);
200
201  // Look at the size of the callee.
202  for (Function::const_iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
203    analyzeBasicBlock(&*BB, TD);
204}
205