Resolved PR33954.
This patch contains two more constraints that aim to reduce the noise cases where we convert CMOV into branch for small gain, and end up spending more cycles due to overhead.
Differential Revision: https://reviews.llvm.org/D36081
llvm-svn: 310352
LLVM compiler recognizes opportunities to transform a branch into IR select instruction(s) - later it will be lowered into X86::CMOV instruction, assuming no other optimization eliminated the SelectInst.
However, it is not always profitable to emit X86::CMOV instruction. For example, branch is preferable over an X86::CMOV instruction when:
1. Branch is well predicted
2. Condition operand is expensive, compared to True-value and the False-value operands
In CodeGenPrepare pass there is a shallow optimization that tries to convert SelectInst into branch, but it is not enough.
This commit, implements machine optimization pass that converts X86::CMOV instruction(s) into branch, based on a conservative heuristic.
Differential Revision: https://reviews.llvm.org/D34769
llvm-svn: 308142
Amjad Aboud