[SLPVectorizer]Migrate getEntryCost to return InstructionCost

Authored by CarolineConcatto on Dec 10 2020, 9:23 AM.


[SLPVectorizer]Migrate getEntryCost to return InstructionCost

This patch also changes:

the return type of getGatherCost and
the signature of the debug function dumpTreeCosts

to use InstructionCost.

This patch is part of a series of patches to use InstructionCost instead of
unsigned/int for the cost model functions.

See this thread for context:

See this patch for the introduction of the type:

Depends on D93049

Differential Revision: https://reviews.llvm.org/D93127