[llvm] [MachineSink] Allow readReg instead of isUse (PR #204610)

[via llvm-commits]

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@@ -2223,12 +2223,7 @@ static bool hasRegisterDependency(MachineInstr *MI,
         break;
       }
       DefedRegsInCopy.push_back(Reg);
-
-      // FIXME: instead of isUse(), readsReg() would be a better fix here,
-      // For example, we can ignore modifications in reg with undef. However,
-      // it's not perfectly clear if skipping the internal read is safe in all
-      // other targets.
-    } else if (MO.isUse()) {
+    } else if (MO.readsReg()) {
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AZero13 wrote:

Note that isDef and readsReg are not mutually exclusive. A subreg def "reads" the parts of reg that are not defined. So maybe the "else" here is not appropriate? I'm not sure what the effect would be of changing that.

Well, putting defs into the UsedOpsInCopy.push_back(i); would be bad it seems. 

https://github.com/llvm/llvm-project/pull/204610