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

[Alex Bradbury via llvm-commits]

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@@ -0,0 +1,91 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc %s -mtriple=riscv64 -regalloc-csr-first-time-cost=0 | FileCheck %s -check-prefix=ZERO-COST
+; RUN: llc %s -mtriple=riscv64 -regalloc-csr-first-time-cost=64 | FileCheck %s -check-prefix=SOME-COST
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asb wrote:

Would it be better to not set `-regalloc-csr-first-time-cost` in the cost=64 case and name it `DEFAULT-COST`. Then this test will fail if the default behaviour is changed (e.g. having getCSRFirstUseCost return 0).

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