[llvm] [RISCV][NFC] Adopt DiagnosticString interface (PR #126290)

[Craig Topper via llvm-commits]

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@@ -150,12 +151,26 @@ def SPMem : MemOperand<SP>;
 
 def GPRCMem : MemOperand<GPRC>;
 
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topperc wrote:

I guess this makes a bunch of similar strings in the final binary that can no longer be shared?

https://github.com/llvm/llvm-project/pull/126290