[llvm] [Mips] Fix atomic min/max generate mips4 instructions when compiling … (PR #159717)

[Matt Arsenault via llvm-commits]

================
@@ -829,20 +882,35 @@ bool MipsExpandPseudo::expandAtomicBinOp(MachineBasicBlock &BB,
     BuildMI(loopMBB, DL, TII->get(OR), Scratch).addReg(Incr).addReg(ZERO);
   }
 
-  BuildMI(loopMBB, DL, TII->get(SC), Scratch)
-      .addReg(Scratch)
-      .addReg(Ptr)
-      .addImm(0);
-  BuildMI(loopMBB, DL, TII->get(BEQ))
-      .addReg(Scratch)
-      .addReg(ZERO)
-      .addMBB(loopMBB);
+  if (NoMovnInstr) {
+    BuildMI(loop2MBB, DL, TII->get(SC), Scratch)
+        .addReg(Scratch)
+        .addReg(Ptr)
+        .addImm(0);
+    BuildMI(loop2MBB, DL, TII->get(BEQ))
+        .addReg(Scratch)
+        .addReg(ZERO)
+        .addMBB(loopMBB);
+  } else {
+    BuildMI(loopMBB, DL, TII->get(SC), Scratch)
+        .addReg(Scratch)
+        .addReg(Ptr)
+        .addImm(0);
+    BuildMI(loopMBB, DL, TII->get(BEQ))
+        .addReg(Scratch)
+        .addReg(ZERO)
+        .addMBB(loopMBB);
+  }
 
   NMBBI = BB.end();
   I->eraseFromParent();
 
   LivePhysRegs LiveRegs;
   computeAndAddLiveIns(LiveRegs, *loopMBB);
+  if (loop1MBB)
+    computeAndAddLiveIns(LiveRegs, *loop1MBB);
+  if (loop2MBB)
+    computeAndAddLiveIns(LiveRegs, *loop2MBB);
----------------
arsenm wrote:

```suggestion
  if (loop1MBB) {
    assert(loop2MBB && "should have 2 loop blocks");
    computeAndAddLiveIns(LiveRegs, *loop1MBB);
    computeAndAddLiveIns(LiveRegs, *loop2MBB);
  }
```

https://github.com/llvm/llvm-project/pull/159717