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Add documentation. 

llvm-svn: 167055
This commit is contained in:
Nadav Rotem 2012-10-30 22:06:26 +00:00
parent 616e8a5c0b
commit 47a299dcc9
1 changed files with 5 additions and 0 deletions
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5
llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
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@ -749,16 +749,21 @@ SingleBlockLoopVectorizer::createEmptyLoop(LoopVectorizationLegality *Legal) {
}
/// This function returns the identity element (or neutral element) for
/// the operation K.
static unsigned
getReductionIdentity(LoopVectorizationLegality::ReductionKind K) {
switch (K) {
case LoopVectorizationLegality::IntegerXor:
case LoopVectorizationLegality::IntegerAdd:
case LoopVectorizationLegality::IntegerOr:
// Adding, Xoring, Oring zero to a number does not change it.
return 0;
case LoopVectorizationLegality::IntegerMult:
// Multiplying a number by 1 does not change it.
return 1;
case LoopVectorizationLegality::IntegerAnd:
// AND-ing a number with an all-1 value does not change it.
return -1;
default:
llvm_unreachable("Unknown reduction kind");