[llvm] [MIPS]: Rework atomic max/min expand for subword (PR #89575)

[via llvm-commits]

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@@ -473,48 +476,38 @@ bool MipsExpandPseudo::expandAtomicBinOpSubword(
     unsigned SELOldVal = IsMax ? SELEQZ : SELNEZ;
     unsigned MOVIncr = IsMax ? MOVN : MOVZ;
 
-    // For little endian we need to clear uninterested bits.
-    if (STI->isLittle()) {
-      if (!IsUnsigned) {
-        BuildMI(loopMBB, DL, TII->get(Mips::SRAV), OldVal)
-            .addReg(OldVal)
-            .addReg(ShiftAmnt);
-        BuildMI(loopMBB, DL, TII->get(Mips::SRAV), Incr)
-            .addReg(Incr)
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yingopq wrote:

@wzssyqa Do I need to remove the ```RegState::Kill``` of ```StoreVal```? The current test has not found any problems related to this. But I once encountered a problem related to ```RegState::Kill``` when I create a new reg like ```Scratch``` in function ```MachineBasicBlock *MipsTargetLowering::emitAtomicBinaryPartword``` and use it in function ```bool MipsExpandPseudo::expandAtomicBinOpSubword``` to replace ```OldVal```, and when the code is executed to ```slt```, an error is reported.

https://github.com/llvm/llvm-project/pull/89575