[PATCH] D13417: [MachineCombiner] remove "slack" from critical path cost calculation (PR25016)

[Gerolf Hoflehner via llvm-commits]

Gerolf added a subscriber: Gerolf.
Gerolf added a comment.

Taking the slack into account was necessary for the madd combiner to avoid regressions on a number of benchmarks. The new instruction sequence may use up the slack w/o extending the critical path. This change makes the heuristic too conservative. We should not change an heuristic for a fast-math optimization that impacts everything else.

-Gerolf


http://reviews.llvm.org/D13417