[llvm] [CodeGen] Add generic INIT_UNDEF pseudo (PR #106744)

[Nikita Popov via llvm-commits]

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@@ -1254,6 +1254,13 @@ def IMPLICIT_DEF : StandardPseudoInstruction {
   let isAsCheapAsAMove = true;
   let isMeta = true;
 }
+def INIT_UNDEF : StandardPseudoInstruction {
+  let OutOperandList = (outs unknown:$dst);
+  let InOperandList = (ins);
+  let AsmString = "";
+  let hasSideEffects = false;
+  let Size = 0;
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nikic wrote:

I initially also added `isMeta = true` here like IMPLICIT_DEF does, but this caused more (positive looking) changes in riscv, so I left it out again.

Disclaimer: I don't really know what I'm doing here... or what exactly the effect of isMeta is.

https://github.com/llvm/llvm-project/pull/106744