[llvm] [RISCV] Override default sched policy (PR #115445)

[Min-Yih Hsu via llvm-commits]

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@@ -199,3 +200,25 @@ unsigned RISCVSubtarget::getMinimumJumpTableEntries() const {
              ? RISCVMinimumJumpTableEntries
              : TuneInfo->MinimumJumpTableEntries;
 }
+
+void RISCVSubtarget::overrideSchedPolicy(MachineSchedPolicy &Policy,
+                                         unsigned NumRegionInstrs) const {
+  // Do bidirectional scheduling since it provides a more balanced scheduling
+  // leading to better performance. This will increase compile time.
+  Policy.OnlyTopDown = false;
+  Policy.OnlyBottomUp = false;
+
+  // Enabling or Disabling the latency heuristic is a close call: It seems to
+  // help nearly no benchmark on out-of-order architectures, on the other hand
+  // it regresses register pressure on a few benchmarking.
+  // FIXME: This is from AArch64, but we haven't evaluated it on RISC-V.
+  Policy.DisableLatencyHeuristic = true;
----------------
mshockwave wrote:

> Maybe we should enable this for in-oder cores?

Personally I would not disabling it at all because as I mentioned before, I don't think program order is any better than reducing critical path, regardless of in-order or out-of-order cores.

That said, I'm fine with enabling it for in-order cores for now and see how it goes.

https://github.com/llvm/llvm-project/pull/115445