diff --git a/llvm/include/llvm/CodeGen/TargetLowering.h b/llvm/include/llvm/CodeGen/TargetLowering.h
--- a/llvm/include/llvm/CodeGen/TargetLowering.h
+++ b/llvm/include/llvm/CodeGen/TargetLowering.h
@@ -2959,6 +2959,9 @@
   /// Check whether or not \p MI needs to be moved close to its uses.
   virtual bool shouldLocalize(const MachineInstr &MI, const TargetTransformInfo *TTI) const;
 
+  /// GlobalISel version of TargetLowering::AdjustInstrPostInstrSelection.
+  /// Returns true if the MIR was modified.
+  virtual bool adjustInstrPostGISel(MachineInstr &MI) const;
 
 private:
   const TargetMachine &TM;
diff --git a/llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp b/llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp
--- a/llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp
@@ -133,6 +133,9 @@
   // Keep track of selected blocks, so we can delete unreachable ones later.
   DenseSet<MachineBasicBlock *> SelectedBlocks;
 
+  // List of newly added MachineInstrs during selection.
+  SmallVector<MachineInstr *, 8> InsertedMIs;
+
   for (MachineBasicBlock *MBB : post_order(&MF)) {
     ISel->CurMBB = MBB;
     SelectedBlocks.insert(MBB);
@@ -144,10 +147,8 @@
     bool ReachedBegin = false;
     for (auto MII = std::prev(MBB->end()), Begin = MBB->begin();
          !ReachedBegin;) {
-#ifndef NDEBUG
-      // Keep track of the insertion range for debug printing.
+
       const auto AfterIt = std::next(MII);
-#endif
       // Select this instruction.
       MachineInstr &MI = *MII;
 
@@ -193,14 +194,13 @@
         return false;
       }
 
-      // Dump the range of instructions that MI expanded into.
-      LLVM_DEBUG({
-        auto InsertedBegin = ReachedBegin ? MBB->begin() : std::next(MII);
-        dbgs() << "Into:\n";
-        for (auto &InsertedMI : make_range(InsertedBegin, AfterIt))
-          dbgs() << "  " << InsertedMI;
-        dbgs() << '\n';
-      });
+      auto InsertedBegin = ReachedBegin ? MBB->begin() : std::next(MII);
+      LLVM_DEBUG(dbgs() << "Into:\n");
+      for (auto &InsertedMI : make_range(InsertedBegin, AfterIt)) {
+        InsertedMIs.push_back(&InsertedMI);
+        LLVM_DEBUG(dbgs() << "  " << InsertedMI);
+      }
+      LLVM_DEBUG(dbgs() << '\n');
     }
   }
 
@@ -304,6 +304,16 @@
   auto &TLI = *MF.getSubtarget().getTargetLowering();
   TLI.finalizeLowering(MF);
 
+  for (MachineInstr *MI : InsertedMIs) {
+    if (MI->hasPostISelHook()) {
+      LLVM_DEBUG(dbgs() << "hasPostISelHook handling of:\n  " << *MI);
+      bool Modified = TLI.adjustInstrPostGISel(*MI);
+      (void)Modified;
+      LLVM_DEBUG(if (Modified) dbgs() << "Modified To:\n  " << *MI;
+                 else dbgs() << "Didn't modify\n";);
+    }
+  }
+
   LLVM_DEBUG({
     dbgs() << "Rules covered by selecting function: " << MF.getName() << ":";
     for (auto RuleID : CoverageInfo.covered())
diff --git a/llvm/lib/CodeGen/TargetLoweringBase.cpp b/llvm/lib/CodeGen/TargetLoweringBase.cpp
--- a/llvm/lib/CodeGen/TargetLoweringBase.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringBase.cpp
@@ -2361,3 +2361,9 @@
   }
   }
 }
+
+bool TargetLoweringBase::adjustInstrPostGISel(MachineInstr &MI) const {
+  // TODO: Add assertion for MI.hasPostISelHook() once every global-isel target
+  // overrides this function.
+  return false;
+}