set div/rem default values to 'expensive' in TargetTransformInfo's
cost model
...because that's what the cost model was intended to do.
As discussed in D12882, this fix has a temporary unintended
consequence for SimplifyCFG: it causes us to not speculate an fdiv.
However, two wrongs make PR24818 right, and two wrongs make PR24343
act right even though it's really still wrong.
I intend to correct SimplifyCFG and add to CodeGenPrepare to account
for this cost model change and preserve the righteousness for the bug
report cases.
https://llvm.org/bugs/show_bug.cgi?id=24818https://llvm.org/bugs/show_bug.cgi?id=24343
Differential Revision: http://reviews.llvm.org/D12882
This fixes the too-eager fdiv hoisting in pow(), which could lead to
unexpected floating point exceptions.
a502cd2f72