http://llvm.org/bugs/show_bug.cgi?id=11991
Bug #: 11991
Summary: BB vectorizer search for pair vector instructions is
O(n^2) and can be improved to be O(n)
Product: new-bugs
Version: unspecified
Platform: PC
OS/Version: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected], [email protected]
Classification: Unclassified
Currently the BB vectorizer has a complexity of O(n^2) in the number
of instructions in a basic block. This is due to the search algorithm
for vectorizable instructions pairs:
for i in BBinstructions
for j in BBinstructions
if (isVectPairable(i, j))
push pair(i, j)
This can be improved in an algorithm that is O(n*t) in number of
instructions times the number of vectorizable types, and because the
number of types that can be vectorized are finite, the algorithm is
actually O(n):
for i in BBinstructions
if (isVectorizableType1(i))
push i into Type1Instructions
else if (isVectorizableType2(i))
push i into Type2Instructions
etc.
In the end we get all vectorizable pairs by their types in these vectors.
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