[llvm] [RISCV] add load/store misched/PostRA cluster options (PR #149409)

[Daniel Henrique Barboza via llvm-commits]

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@@ -94,14 +94,24 @@ static cl::opt<bool>
                            cl::desc("Enable the loop data prefetch pass"),
                            cl::init(true));
 
-static cl::opt<bool> EnableMISchedLoadStoreClustering(
-    "riscv-misched-load-store-clustering", cl::Hidden,
-    cl::desc("Enable load and store clustering in the machine scheduler"),
+static cl::opt<bool> EnableMISchedLoadClustering(
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danielhb wrote:

By Subtarget feature are we talking about a a feature, like FeatureUnalignedScalarMem, or a tune like TunePostRAScheduler (took the examples from sifive_p670)? Seems to me that this would be more like a tuning like PostRAScheduler.

Also, do we want to keep the default as is (enable all load/store clustering in both stages) and add features to disable it, or the other way around? Having everything disabled by default and adding subtarget features to enable what you want is cleaner, but  we'll change behavior for everyone that doesn't add the new features in their target defs. Perhaps this is a good thing (we'll force people to make a decision instead of relying on defaults) ....

https://github.com/llvm/llvm-project/pull/149409