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This commit adds scoped noalias metadata. The primary motivations for this feature are: 1. To preserve noalias function attribute information when inlining 2. To provide the ability to model block-scope C99 restrict pointers Neither of these two abilities are added here, only the necessary infrastructure. In fact, there should be no change to existing functionality, only the addition of new features. The logic that converts noalias function parameters into this metadata during inlining will come in a follow-up commit. What is added here is the ability to generally specify noalias memory-access sets. Regarding the metadata, alias-analysis scopes are defined similar to TBAA nodes: !scope0 = metadata !{ metadata !"scope of foo()" } !scope1 = metadata !{ metadata !"scope 1", metadata !scope0 } !scope2 = metadata !{ metadata !"scope 2", metadata !scope0 } !scope3 = metadata !{ metadata !"scope 2.1", metadata !scope2 } !scope4 = metadata !{ metadata !"scope 2.2", metadata !scope2 } Loads and stores can be tagged with an alias-analysis scope, and also, with a noalias tag for a specific scope: ... = load %ptr1, !alias.scope !{ !scope1 } ... = load %ptr2, !alias.scope !{ !scope1, !scope2 }, !noalias !{ !scope1 } When evaluating an aliasing query, if one of the instructions is associated with an alias.scope id that is identical to the noalias scope associated with the other instruction, or is a descendant (in the scope hierarchy) of the noalias scope associated with the other instruction, then the two memory accesses are assumed not to alias. Note that is the first element of the scope metadata is a string, then it can be combined accross functions and translation units. The string can be replaced by a self-reference to create globally unqiue scope identifiers. [Note: This overview is slightly stylized, since the metadata nodes really need to just be numbers (!0 instead of !scope0), and the scope lists are also global unnamed metadata.] Existing noalias metadata in a callee is "cloned" for use by the inlined code. This is necessary because the aliasing scopes are unique to each call site (because of possible control dependencies on the aliasing properties). For example, consider a function: foo(noalias a, noalias b) { *a = *b; } that gets inlined into bar() { ... if (...) foo(a1, b1); ... if (...) foo(a2, b2); } -- now just because we know that a1 does not alias with b1 at the first call site, and a2 does not alias with b2 at the second call site, we cannot let inlining these functons have the metadata imply that a1 does not alias with b2. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213864 91177308-0d34-0410-b5e6-96231b3b80d8 |
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.. | ||
IPA | ||
AliasAnalysis.cpp | ||
AliasAnalysisCounter.cpp | ||
AliasAnalysisEvaluator.cpp | ||
AliasDebugger.cpp | ||
AliasSetTracker.cpp | ||
Analysis.cpp | ||
BasicAliasAnalysis.cpp | ||
BlockFrequencyInfo.cpp | ||
BlockFrequencyInfoImpl.cpp | ||
BranchProbabilityInfo.cpp | ||
CaptureTracking.cpp | ||
CFG.cpp | ||
CFGPrinter.cpp | ||
CGSCCPassManager.cpp | ||
CMakeLists.txt | ||
CodeMetrics.cpp | ||
ConstantFolding.cpp | ||
CostModel.cpp | ||
Delinearization.cpp | ||
DependenceAnalysis.cpp | ||
DominanceFrontier.cpp | ||
DomPrinter.cpp | ||
InstCount.cpp | ||
InstructionSimplify.cpp | ||
Interval.cpp | ||
IntervalPartition.cpp | ||
IVUsers.cpp | ||
JumpInstrTableInfo.cpp | ||
LazyCallGraph.cpp | ||
LazyValueInfo.cpp | ||
LibCallAliasAnalysis.cpp | ||
LibCallSemantics.cpp | ||
Lint.cpp | ||
LLVMBuild.txt | ||
Loads.cpp | ||
LoopInfo.cpp | ||
LoopPass.cpp | ||
Makefile | ||
MemDepPrinter.cpp | ||
MemoryBuiltins.cpp | ||
MemoryDependenceAnalysis.cpp | ||
ModuleDebugInfoPrinter.cpp | ||
NoAliasAnalysis.cpp | ||
PHITransAddr.cpp | ||
PostDominators.cpp | ||
PtrUseVisitor.cpp | ||
README.txt | ||
RegionInfo.cpp | ||
RegionPass.cpp | ||
RegionPrinter.cpp | ||
ScalarEvolution.cpp | ||
ScalarEvolutionAliasAnalysis.cpp | ||
ScalarEvolutionExpander.cpp | ||
ScalarEvolutionNormalization.cpp | ||
ScopedNoAliasAA.cpp | ||
SparsePropagation.cpp | ||
TargetTransformInfo.cpp | ||
Trace.cpp | ||
TypeBasedAliasAnalysis.cpp | ||
ValueTracking.cpp |
Analysis Opportunities: //===---------------------------------------------------------------------===// In test/Transforms/LoopStrengthReduce/quadradic-exit-value.ll, the ScalarEvolution expression for %r is this: {1,+,3,+,2}<loop> Outside the loop, this could be evaluated simply as (%n * %n), however ScalarEvolution currently evaluates it as (-2 + (2 * (trunc i65 (((zext i64 (-2 + %n) to i65) * (zext i64 (-1 + %n) to i65)) /u 2) to i64)) + (3 * %n)) In addition to being much more complicated, it involves i65 arithmetic, which is very inefficient when expanded into code. //===---------------------------------------------------------------------===// In formatValue in test/CodeGen/X86/lsr-delayed-fold.ll, ScalarEvolution is forming this expression: ((trunc i64 (-1 * %arg5) to i32) + (trunc i64 %arg5 to i32) + (-1 * (trunc i64 undef to i32))) This could be folded to (-1 * (trunc i64 undef to i32)) //===---------------------------------------------------------------------===//