[llvm] [AMDGPU] Support function attribute to override postRA scheduling direction (PR #147708)

[Carl Ritson via llvm-commits]

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@@ -1144,6 +1144,23 @@ GCNTargetMachine::createMachineScheduler(MachineSchedContext *C) const {
 
 ScheduleDAGInstrs *
 GCNTargetMachine::createPostMachineScheduler(MachineSchedContext *C) const {
+  Attribute PostRADirectionAttr =
+      C->MF->getFunction().getFnAttribute("misched-postra-direction");
+
+  if (PostRADirectionAttr.isValid()) {
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perlfu wrote:

Code changes do not seem to solve either of the two issues I mentioned.

New option `AMDGPUPostRADirection` is not connected, and would not solve the issue of function attribute overriding the direction of *all* machine schedulers.
To fix this issue, the direction needs to be passed at scheduler construction or otherwise stored/updated in the scheduler object.
i.e. there needs to be a per-scheduler way of setting direction that doesn't currently exist.

To avoid a function attribute overriding command line options, you should check for presence of command line option before parsing function attribute.
Then ignore the function attribute if a command line option is already present/set.
Again you don't need to do this part if the command line override applies to a per-scheduler direction as implemented above -- this detail can be encapsulated within the MachineScheduler code, then AMDGPU code only need set the desired direction.

https://github.com/llvm/llvm-project/pull/147708