[llvm] [RISCV] Support PreserveMost calling convention (PR #148214)

[Craig Topper via llvm-commits]

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@@ -93,3 +93,5 @@ def CSR_XLEN_F32_V_Interrupt_RVE: CalleeSavedRegs<(sub CSR_XLEN_F32_V_Interrupt,
 // Same as CSR_XLEN_F64_V_Interrupt, but excluding X16-X31.
 def CSR_XLEN_F64_V_Interrupt_RVE: CalleeSavedRegs<(sub CSR_XLEN_F64_V_Interrupt,
                                                    (sequence "X%u", 16, 31))>;
+
+def CSR_RT_MostRegs : CalleeSavedRegs<(add (sequence "X%u", 5, 31))>;
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topperc wrote:

Do we need to include X1?

https://github.com/llvm/llvm-project/pull/148214