[llvm] [X86] Add MI-layer routine for getting the index of the first address operand (PR #78019)

[Phoebe Wang via llvm-commits]

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@@ -1365,7 +1358,7 @@ void X86SpeculativeLoadHardeningPass::tracePredStateThroughBlocksAndHarden(
         // could prune out subsequent loads.
         if (EnablePostLoadHardening && X86InstrInfo::isDataInvariantLoad(MI) &&
             !isEFLAGSDefLive(MI) && MI.getDesc().getNumDefs() == 1 &&
-            MI.getOperand(0).isReg() &&
+            MI.getOperand(0).isReg() && MI.getOperand(0).getReg().isVirtual() &&
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phoebewang wrote:

Do not put unrelated change in one patch.

https://github.com/llvm/llvm-project/pull/78019