[llvm] [RISCV][RegAlloc] Add getCSRFirstUseCost for RISC-V (PR #131349)

[Craig Topper via llvm-commits]

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@@ -2375,10 +2375,12 @@ void RAGreedy::aboutToRemoveInterval(const LiveInterval &LI) {
 }
 
 void RAGreedy::initializeCSRCost() {
-  // We use the larger one out of the command-line option and the value report
-  // by TRI.
+  // We use the command-line option if it is explicitly set, otherwise use the
+  // larger one out of the command-line option and the value reported by TRI.
   CSRCost = BlockFrequency(
-      std::max((unsigned)CSRFirstTimeCost, TRI->getCSRFirstUseCost()));
+      CSRFirstTimeCost.getNumOccurrences()
+          ? CSRFirstTimeCost
+          : std::max((unsigned)CSRFirstTimeCost, TRI->getCSRFirstUseCost()));
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topperc wrote:

I guess, but I'm not sure why the default of the `CSRFirstTimeCost` would be changed instead of the base class implementation of `TargetRegisterInfo::getCSRFirstUseCost()`.

We can take the code how you have it.

https://github.com/llvm/llvm-project/pull/131349