Try to clarify this comment some.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152221 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2012-03-07 10:13:40 +00:00
parent a1eb50fe3d
commit b53a1d67b1

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@ -1850,10 +1850,13 @@ MachineInstrExpressionTrait::getHashValue(const MachineInstr* const &MI) {
// MachineOperand, but currently that doesn't work because there are many
// different ideas of "equality" and thus different sets of information that
// contribute to the hash code. This one happens to want to take a specific
// subset. It's not clear that this routine uses the correct set of
// information, it would be good to somehow ensure this function is
// MachineInstr::isIdenticalTo with the 'IgnoreVRegDefs' filter look at the
// same bits.
// subset. And it's still not clear that this routine uses the *correct*
// subset of information when computing the hash code. The goal is to use the
// same inputs for the hash code here that MachineInstr::isIdenticalTo uses to
// test for equality when passed the 'IgnoreVRegDefs' filter flag. It would
// be very useful to factor the selection of relevant inputs out of the two
// functions and into a common routine, but it's not clear how that can be
// done.
SmallVector<size_t, 8> HashComponents;
HashComponents.reserve(MI->getNumOperands() + 1);
HashComponents.push_back(MI->getOpcode());