[llvm-dev] Loop branching inefficiencies in Backend output
Friedman, Eli via llvm-dev
llvm-dev at lists.llvm.org
Mon Jul 10 13:01:29 PDT 2017
On 7/9/2017 4:36 PM, Dilan Manatunga via llvm-dev wrote:
> When I looked at the debug output for the x86 backend though, I can't
> figure out how they realize to get rid of that branch. Up to the last
> point that MachineInstrs are printed (the rewrite virtual registers
> pass), the MachineInstrs still show the two jump paradigm. But in the
> final output, it somehow becomes one branch case.
The "-print-after-all" flag is often useful to figure out what various
> I know one solution is for me to add a pass after basic block
> placement to change these instructions, but I am wondering if there is
> a recommended way to do this. Especially as this seems like a common
> problem, where an existing generic pass would have some interface a
> backend should support to allow branch re-writes to create the single
> branch case.
This transform already exists as target-independent code in
BranchFolding.cpp. Is TargetInstrInfo::reverseBranchCondition
implemented for your target?
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