[llvm] [PowerPC] using milicode call for strlen instead of lib call (PR #153600)

[Lei Huang via llvm-commits]

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@@ -1259,6 +1259,9 @@ class SelectionDAG {
   std::pair<SDValue, SDValue> getMemcmp(SDValue Chain, const SDLoc &dl,
                                         SDValue Dst, SDValue Src, SDValue Size,
                                         const CallInst *CI);
+  LLVM_ABI std::pair<SDValue, SDValue>
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lei137 wrote:

nit: can we add some doc on what this function does?
What is the difference between returing `LLVM_ABI std::pair<SDValue, SDValue>` vs just `std::pair<SDValue, SDValue>`?  I see that `getMemcmp()` doesn't use `LLVM_ABI`

https://github.com/llvm/llvm-project/pull/153600