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remove constant terms

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The delinearization is needed only to remove the non linearity induced by
expressions involving multiplications of parameters and induction variables.
There is no problem in dealing with constant times parameters, or constant times
an induction variable.

For this reason, the current patch discards all constant terms and multipliers
before running the delinearization algorithm on the terms. The only thing
remaining in the term expressions are parameters and multiply expressions of
parameters: these simplified term expressions are passed to the array shape
recognizer that will not recognize constant dimensions anymore: these will be
recognized as different strides in parametric subscripts.

The only important special case of a constant dimension is the size of elements.
Instead of relying on the delinearization to infer the size of an element,
compute the element size from the base address type. This is a much more precise
way of computing the element size than before, as we would have mixed together
the size of an element with the strides of the innermost dimension.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209691 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sebastian Pop
2014-05-27 22:41:45 +00:00
parent 50adf38080
commit 421b2c571c
8 changed files with 140 additions and 34 deletions
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3
include/llvm/Analysis/DependenceAnalysis.h
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@@ -910,7 +910,8 @@ namespace llvm {
const Constraint &CurConstraint) const;
bool tryDelinearize(const SCEV *SrcSCEV, const SCEV *DstSCEV,
SmallVectorImpl<Subscript> &Pair) const;
SmallVectorImpl<Subscript> &Pair,
const SCEV *ElementSize) const;
public:
static char ID; // Class identification, replacement for typeinfo

6
include/llvm/Analysis/ScalarEvolution.h
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@@ -894,10 +894,14 @@ namespace llvm {
/// indirect operand.
bool hasOperand(const SCEV *S, const SCEV *Op) const;
/// Return the size of an element read or written by Inst.
const SCEV *getElementSize(Instruction *Inst);
/// Compute the array dimensions Sizes from the set of Terms extracted from
/// the memory access function of this SCEVAddRecExpr.
void findArrayDimensions(SmallVectorImpl<const SCEV *> &Terms,
SmallVectorImpl<const SCEV *> &Sizes) const;
SmallVectorImpl<const SCEV *> &Sizes,
const SCEV *ElementSize) const;
bool runOnFunction(Function &F) override;
void releaseMemory() override;

3
include/llvm/Analysis/ScalarEvolutionExpressions.h
View File

@@ -434,7 +434,8 @@ namespace llvm {
/// Overall, we have: A[][n][m], and the access function: A[j+k][2i][5i].
const SCEV *delinearize(ScalarEvolution &SE,
SmallVectorImpl<const SCEV *> &Subscripts,
SmallVectorImpl<const SCEV *> &Sizes) const;
SmallVectorImpl<const SCEV *> &Sizes,
const SCEV *ElementSize) const;
};
//===--------------------------------------------------------------------===//