[clang] [llvm] [RISCV] Add partial support for -fzero-call-used-regs (PR #194883)

[Sam Elliott via cfe-commits]

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@@ -2128,6 +2128,13 @@ def SetFCSRImm : SetSysRegImm<SysRegFCSR, [FRM, FFLAGS]>;
 
 /// Other pseudo-instructions
 
+// Used by -fzero-call-used-regs to zero out registers.
+let hasSideEffects = 0, mayLoad = 0, mayStore = 0, Size = 8,
+    isCodeGenOnly = 0 in
+def PseudoClearGPR : Pseudo<(outs GPR:$rd), (ins), [],
+                             "clear_gpr", "$rd">,
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lenary wrote:

```suggestion
    isCodeGenOnly = true in
def PseudoClearGPR : Pseudo<(outs GPR:$rd), (ins), []>,
```

https://github.com/llvm/llvm-project/pull/194883