diff --git a/include/llvm/CodeGen/MachineFunction.h b/include/llvm/CodeGen/MachineFunction.h
index 1083e397c2a..9043256e8a9 100644
--- a/include/llvm/CodeGen/MachineFunction.h
+++ b/include/llvm/CodeGen/MachineFunction.h
@@ -618,6 +618,14 @@ public:
     BasicBlocks.sort(comp);
   }
 
+  /// Return the number of \p MachineInstrs in this \p MachineFunction.
+  unsigned getInstructionCount() const {
+    unsigned InstrCount = 0;
+    for (const MachineBasicBlock &MBB : BasicBlocks)
+      InstrCount += MBB.size();
+    return InstrCount;
+  }
+
   //===--------------------------------------------------------------------===//
   // Internal functions used to automatically number MachineBasicBlocks
 
diff --git a/lib/CodeGen/MachineFunctionPass.cpp b/lib/CodeGen/MachineFunctionPass.cpp
index 67ac95740e3..5db4e299fa7 100644
--- a/lib/CodeGen/MachineFunctionPass.cpp
+++ b/lib/CodeGen/MachineFunctionPass.cpp
@@ -23,11 +23,13 @@
 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 
 using namespace llvm;
+using namespace ore;
 
 Pass *MachineFunctionPass::createPrinterPass(raw_ostream &O,
                                              const std::string &Banner) const {
@@ -57,9 +59,43 @@ bool MachineFunctionPass::runOnFunction(Function &F) {
     llvm_unreachable("MachineFunctionProperties check failed");
   }
 #endif
+  // Collect the MI count of the function before the pass.
+  unsigned CountBefore, CountAfter;
+
+  // Check if the user asked for size remarks.
+  bool ShouldEmitSizeRemarks =
+      F.getParent()->shouldEmitInstrCountChangedRemark();
+
+  // If we want size remarks, collect the number of MachineInstrs in our
+  // MachineFunction before the pass runs.
+  if (ShouldEmitSizeRemarks)
+    CountBefore = MF.getInstructionCount();
 
   bool RV = runOnMachineFunction(MF);
 
+  if (ShouldEmitSizeRemarks) {
+    // We wanted size remarks. Check if there was a change to the number of
+    // MachineInstrs in the module. Emit a remark if there was a change.
+    CountAfter = MF.getInstructionCount();
+    if (CountBefore != CountAfter) {
+      MachineOptimizationRemarkEmitter MORE(MF, nullptr);
+      MORE.emit([&]() {
+        int64_t Delta = static_cast<int64_t>(CountAfter) -
+                        static_cast<int64_t>(CountBefore);
+        MachineOptimizationRemarkAnalysis R("size-info", "FunctionMISizeChange",
+                                            MF.getFunction().getSubprogram(),
+                                            &MF.front());
+        R << NV("Pass", getPassName())
+          << ": Function: " << NV("Function", F.getName()) << ": "
+          << "MI Instruction count changed from "
+          << NV("MIInstrsBefore", CountBefore) << " to "
+          << NV("MIInstrsAfter", CountAfter)
+          << "; Delta: " << NV("Delta", Delta);
+        return R;
+      });
+    }
+  }
+
   MFProps.set(SetProperties);
   MFProps.reset(ClearedProperties);
   return RV;
diff --git a/test/Other/machine-size-remarks.ll b/test/Other/machine-size-remarks.ll
new file mode 100644
index 00000000000..188676db8b3
--- /dev/null
+++ b/test/Other/machine-size-remarks.ll
@@ -0,0 +1,58 @@
+; RUN: llc -mtriple x86_64---- %s -pass-remarks-analysis='size-info'\
+; RUN: -pass-remarks-output=%t.yaml -o /dev/null < %s 2> %t; \
+; RUN: cat %t %t.yaml | FileCheck %s
+
+; Make sure that machine-level size remarks work.
+; Test the following:
+; - When we create a MachineFunction (e.g, during instruction selection), it
+;   has a size of 0.
+; - The initial size of the function after filling it is positive.
+; - After that, we can increase or decrease the size of the function.
+; - ... The final size must be positive.
+; - ... The delta can be negative or positive.
+
+; CHECK: remark: <unknown>:0:0: X86 DAG->DAG Instruction Selection: Function:
+; CHECK-SAME: main: MI Instruction count changed from 0
+; CHECK-SAME: to [[INIT:[1-9][0-9]*]]; Delta: [[INIT]]
+; CHECK-NEXT: remark: <unknown>:0:0: Simple Register Coalescing: Function: main:
+; CHECK-SAME: MI Instruction count changed from [[INIT]] to
+; CHECK-SAME: [[FINAL:[1-9][0-9]*]];
+; CHECK-SAME: Delta: [[DELTA:-?[1-9][0-9]*]]
+; CHECK-NEXT: --- !Analysis
+; CHECK-NEXT: Pass:            size-info
+; CHECK-NEXT: Name:            FunctionMISizeChange
+; CHECK-NEXT: Function:        main
+; CHECK-NEXT: Args:
+; CHECK-NEXT: - Pass:            'X86 DAG->DAG Instruction Selection'
+; CHECK-NEXT: - String:          ': Function: '
+; CHECK-NEXT: - Function:        main
+; CHECK-NEXT: - String:          ': '
+; CHECK-NEXT: - String:          'MI Instruction count changed from '
+; CHECK-NEXT: - MIInstrsBefore:  '0'
+; CHECK-NEXT:  - String:          ' to '
+; CHECK-NEXT:  - MIInstrsAfter:   '[[INIT]]'
+; CHECK-NEXT:  - String:          '; Delta: '
+; CHECK-NEXT:  - Delta:           '[[INIT]]'
+; CHECK-DAG: --- !Analysis
+; CHECK-NEXT: Pass:            size-info
+; CHECK-NEXT: Name:            FunctionMISizeChange
+; CHECK-NEXT: Function:        main
+; CHECK-NEXT: Args:
+; CHECK-NEXT:   - Pass:            Simple Register Coalescing
+; CHECK-NEXT:   - String:          ': Function: '
+; CHECK-NEXT:   - Function:        main
+; CHECK-NEXT:   - String:          ': '
+; CHECK-NEXT:   - String:          'MI Instruction count changed from '
+; CHECK-NEXT:   - MIInstrsBefore:  '[[INIT]]'
+; CHECK-NEXT:   - String:          ' to '
+; CHECK-NEXT:   - MIInstrsAfter:   '[[FINAL]]'
+; CHECK-NEXT:   - String:          '; Delta: '
+; CHECK-NEXT:   - Delta:           '[[DELTA]]'
+define i32 @main() #0 {
+entry:
+  %retval = alloca i32, align 4
+  store i32 0, i32* %retval, align 4
+  ret i32 0
+}
+
+attributes #0 = { noinline nounwind optnone ssp uwtable }