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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152699 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick 2012-03-14 04:00:38 +00:00
parent fc7e9ef239
commit cb058d51db
1 changed files with 15 additions and 0 deletions
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15
lib/CodeGen/MachineScheduler.cpp
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@ -113,6 +113,21 @@ SchedDefaultRegistry("default", "Use the target's default scheduler choice.",
/// default scheduler if the target does not set a default.
static ScheduleDAGInstrs *createCommonMachineSched(MachineSchedContext *C);
/// Top-level MachineScheduler pass driver.
///
/// Visit blocks in function order. Divide each block into scheduling regions
/// and visit them bottom-up. This is consistent with the DAG builder, which
/// traverses scheduling regions bottom-up, but not essential.
///
/// This design avoids exposing scheduling boundaries to the DAG builder,
/// simplifying the DAG builder's support for "special" target instructions,
/// while at the same time allowing target schedulers to operate across
/// scheduling boundaries, for example to bundle the boudary instructions
/// without reordering them. This creates complexity, because the target
/// scheduler must update the RegionBegin and RegionEnd positions cached by
/// ScheduleDAGInstrs whenever adding or removing instructions. A much simpler
/// design would be to split blocks at scheduling boundaries, but LLVM has a
/// general bias against block splitting purely for implementation simplicity.
bool MachineScheduler::runOnMachineFunction(MachineFunction &mf) {
// Initialize the context of the pass.
MF = &mf;