llvm-6502/lib/IR/MDBuilder.cpp
Hal Finkel 6f5c609076 Simplify and improve scoped-noalias metadata semantics
In the process of fixing the noalias parameter -> metadata conversion process
that will take place during inlining (which will be committed soon, but not
turned on by default), I have come to realize that the semantics provided by
yesterday's commit are not really what we want. Here's why:

void foo(noalias a, noalias b, noalias c, bool x) {
  *q = x ? a : b;
  *c = *q;
}

Generically, we know that *c does not alias with *a and with *b (so there is an
'and' in what we know we're not), and we know that *q might be derived from *a
or from *b (so there is an 'or' in what we know that we are). So we do not want
the semantics currently, where any noalias scope matching any alias.scope
causes a NoAlias return. What we want to know is that the noalias scopes form a
superset of the alias.scope list (meaning that all the things we know we're not
is a superset of all of things the other instruction might be).

Making that change, however, introduces a composibility problem. If we inline
once, adding the noalias metadata, and then inline again adding more, and we
append new scopes onto the noalias and alias.scope lists each time. But, this
means that we could change what was a NoAlias result previously into a MayAlias
result because we appended an additional scope onto one of the alias.scope
lists. So, instead of giving scopes the ability to have parents (which I had
borrowed from the TBAA implementation, but seems increasingly unlikely to be
useful in practice), I've given them domains. The subset/superset condition now
applies within each domain independently, and we only need it to hold in one
domain. Each time we inline, we add the new scopes in a new scope domain, and
everything now composes nicely. In addition, this simplifies the
implementation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213948 91177308-0d34-0410-b5e6-96231b3b80d8
2014-07-25 15:50:02 +00:00

156 lines
5.7 KiB
C++

//===---- llvm/MDBuilder.cpp - Builder for LLVM metadata ------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the MDBuilder class, which is used as a convenient way to
// create LLVM metadata with a consistent and simplified interface.
//
//===----------------------------------------------------------------------===//
#include "llvm/IR/MDBuilder.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Metadata.h"
using namespace llvm;
MDString *MDBuilder::createString(StringRef Str) {
return MDString::get(Context, Str);
}
MDNode *MDBuilder::createFPMath(float Accuracy) {
if (Accuracy == 0.0)
return nullptr;
assert(Accuracy > 0.0 && "Invalid fpmath accuracy!");
Value *Op = ConstantFP::get(Type::getFloatTy(Context), Accuracy);
return MDNode::get(Context, Op);
}
MDNode *MDBuilder::createBranchWeights(uint32_t TrueWeight,
uint32_t FalseWeight) {
uint32_t Weights[] = {TrueWeight, FalseWeight};
return createBranchWeights(Weights);
}
MDNode *MDBuilder::createBranchWeights(ArrayRef<uint32_t> Weights) {
assert(Weights.size() >= 2 && "Need at least two branch weights!");
SmallVector<Value *, 4> Vals(Weights.size() + 1);
Vals[0] = createString("branch_weights");
Type *Int32Ty = Type::getInt32Ty(Context);
for (unsigned i = 0, e = Weights.size(); i != e; ++i)
Vals[i + 1] = ConstantInt::get(Int32Ty, Weights[i]);
return MDNode::get(Context, Vals);
}
MDNode *MDBuilder::createRange(const APInt &Lo, const APInt &Hi) {
assert(Lo.getBitWidth() == Hi.getBitWidth() && "Mismatched bitwidths!");
// If the range is everything then it is useless.
if (Hi == Lo)
return nullptr;
// Return the range [Lo, Hi).
Type *Ty = IntegerType::get(Context, Lo.getBitWidth());
Value *Range[2] = {ConstantInt::get(Ty, Lo), ConstantInt::get(Ty, Hi)};
return MDNode::get(Context, Range);
}
MDNode *MDBuilder::createAnonymousAARoot(StringRef Name, MDNode *Extra) {
// To ensure uniqueness the root node is self-referential.
MDNode *Dummy = MDNode::getTemporary(Context, ArrayRef<Value*>());
SmallVector<Value *, 3> Args(1, Dummy);
if (Extra)
Args.push_back(Extra);
if (!Name.empty())
Args.push_back(createString(Name));
MDNode *Root = MDNode::get(Context, Args);
// At this point we have
// !0 = metadata !{} <- dummy
// !1 = metadata !{metadata !0} <- root
// Replace the dummy operand with the root node itself and delete the dummy.
Root->replaceOperandWith(0, Root);
MDNode::deleteTemporary(Dummy);
// We now have
// !1 = metadata !{metadata !1} <- self-referential root
return Root;
}
MDNode *MDBuilder::createTBAARoot(StringRef Name) {
return MDNode::get(Context, createString(Name));
}
/// \brief Return metadata for a non-root TBAA node with the given name,
/// parent in the TBAA tree, and value for 'pointsToConstantMemory'.
MDNode *MDBuilder::createTBAANode(StringRef Name, MDNode *Parent,
bool isConstant) {
if (isConstant) {
Constant *Flags = ConstantInt::get(Type::getInt64Ty(Context), 1);
Value *Ops[3] = {createString(Name), Parent, Flags};
return MDNode::get(Context, Ops);
} else {
Value *Ops[2] = {createString(Name), Parent};
return MDNode::get(Context, Ops);
}
}
MDNode *MDBuilder::createAliasScopeDomain(StringRef Name) {
return MDNode::get(Context, createString(Name));
}
MDNode *MDBuilder::createAliasScope(StringRef Name, MDNode *Domain) {
Value *Ops[2] = { createString(Name), Domain };
return MDNode::get(Context, Ops);
}
/// \brief Return metadata for a tbaa.struct node with the given
/// struct field descriptions.
MDNode *MDBuilder::createTBAAStructNode(ArrayRef<TBAAStructField> Fields) {
SmallVector<Value *, 4> Vals(Fields.size() * 3);
Type *Int64 = Type::getInt64Ty(Context);
for (unsigned i = 0, e = Fields.size(); i != e; ++i) {
Vals[i * 3 + 0] = ConstantInt::get(Int64, Fields[i].Offset);
Vals[i * 3 + 1] = ConstantInt::get(Int64, Fields[i].Size);
Vals[i * 3 + 2] = Fields[i].TBAA;
}
return MDNode::get(Context, Vals);
}
/// \brief Return metadata for a TBAA struct node in the type DAG
/// with the given name, a list of pairs (offset, field type in the type DAG).
MDNode *MDBuilder::createTBAAStructTypeNode(
StringRef Name, ArrayRef<std::pair<MDNode *, uint64_t>> Fields) {
SmallVector<Value *, 4> Ops(Fields.size() * 2 + 1);
Type *Int64 = Type::getInt64Ty(Context);
Ops[0] = createString(Name);
for (unsigned i = 0, e = Fields.size(); i != e; ++i) {
Ops[i * 2 + 1] = Fields[i].first;
Ops[i * 2 + 2] = ConstantInt::get(Int64, Fields[i].second);
}
return MDNode::get(Context, Ops);
}
/// \brief Return metadata for a TBAA scalar type node with the
/// given name, an offset and a parent in the TBAA type DAG.
MDNode *MDBuilder::createTBAAScalarTypeNode(StringRef Name, MDNode *Parent,
uint64_t Offset) {
ConstantInt *Off = ConstantInt::get(Type::getInt64Ty(Context), Offset);
Value *Ops[3] = {createString(Name), Parent, Off};
return MDNode::get(Context, Ops);
}
/// \brief Return metadata for a TBAA tag node with the given
/// base type, access type and offset relative to the base type.
MDNode *MDBuilder::createTBAAStructTagNode(MDNode *BaseType, MDNode *AccessType,
uint64_t Offset) {
Type *Int64 = Type::getInt64Ty(Context);
Value *Ops[3] = {BaseType, AccessType, ConstantInt::get(Int64, Offset)};
return MDNode::get(Context, Ops);
}