[CostModel] Model all `extractvalue`s as free.
Summary:
As disscussed in https://reviews.llvm.org/D65148#
1606412,
`extractvalue` don't actually generate any code,
so we should treat them as free.
Reviewers: craig.topper, RKSimon, jnspaulsson, greened, asb, t.p.northover, jmolloy, dmgreen
Reviewed By: jmolloy
Subscribers: javed.absar, hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D66098
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@370339
91177308-0d34-0410-b5e6-
96231b3b80d8