Index: llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
===================================================================
--- llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
+++ llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
@@ -659,6 +659,8 @@
       if (!isa<CallInst>(U) && !isa<InvokeInst>(U))
         continue;
       auto &CS = *cast<CallBase>(U);
+      if (CS.hasFnAttr(Attribute::MinSize))
+        continue;
 
       // If the parent of the call site will never be executed, we don't need
       // to worry about the passed value.
@@ -688,6 +690,9 @@
   /// This function modifies calls to function \p F whose argument at index \p
   /// ArgNo is equal to constant \p C. The calls are rewritten to call function
   /// \p Clone instead.
+  ///
+  /// Callsites that have been marked with the MinSize function attribute won't
+  /// be specialized and rewritten.
   void rewriteCallSites(Function *F, Function *Clone, Argument &Arg,
                         Constant *C) {
     unsigned ArgNo = Arg.getArgNo();
Index: llvm/test/Transforms/FunctionSpecialization/function-specialization-minsize2.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/FunctionSpecialization/function-specialization-minsize2.ll
@@ -0,0 +1,44 @@
+; RUN: opt -function-specialization -func-specialization-size-threshold=3 -S < %s | FileCheck %s
+
+; Checks for callsites that have been annotated with MinSize. No specialisation
+; expected here:
+;
+; CHECK-NOT: @compute.1
+; CHECK-NOT: @compute.2
+
+define i64 @main(i64 %x, i1 %flag) {
+entry:
+  br i1 %flag, label %plus, label %minus
+
+plus:
+  %tmp0 = call i64 @compute(i64 %x, i64 (i64)* @plus) #0
+  br label %merge
+
+minus:
+  %tmp1 = call i64 @compute(i64 %x, i64 (i64)* @minus) #0
+  br label %merge
+
+merge:
+  %tmp2 = phi i64 [ %tmp0, %plus ], [ %tmp1, %minus]
+  ret i64 %tmp2
+}
+
+define internal i64 @compute(i64 %x, i64 (i64)* %binop) {
+entry:
+  %tmp0 = call i64 %binop(i64 %x)
+  ret i64 %tmp0
+}
+
+define internal i64 @plus(i64 %x) {
+entry:
+  %tmp0 = add i64 %x, 1
+  ret i64 %tmp0
+}
+
+define internal i64 @minus(i64 %x) {
+entry:
+  %tmp0 = sub i64 %x, 1
+  ret i64 %tmp0
+}
+
+attributes #0 = { minsize optsize }
Index: llvm/test/Transforms/FunctionSpecialization/function-specialization-minsize3.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/FunctionSpecialization/function-specialization-minsize3.ll
@@ -0,0 +1,48 @@
+; RUN: opt -function-specialization -func-specialization-size-threshold=3 -S < %s | FileCheck %s
+
+; Checks for callsites that have been annotated with MinSize. We only expect
+; specialisation for the call that does not have the attribute:
+;
+; CHECK: plus:
+; CHECK:   %tmp0 = call i64 @compute.1(i64 %x, i64 (i64)* @plus)
+; CHECK:   br label %merge
+; CHECK: minus:
+; CHECK:   %tmp1 = call i64 @compute(i64 %x, i64 (i64)* @minus) #0
+; CHECK:   br label %merge
+;
+define i64 @main(i64 %x, i1 %flag) {
+entry:
+  br i1 %flag, label %plus, label %minus
+
+plus:
+  %tmp0 = call i64 @compute(i64 %x, i64 (i64)* @plus)
+  br label %merge
+
+minus:
+  %tmp1 = call i64 @compute(i64 %x, i64 (i64)* @minus) #0
+  br label %merge
+
+merge:
+  %tmp2 = phi i64 [ %tmp0, %plus ], [ %tmp1, %minus]
+  ret i64 %tmp2
+}
+
+define internal i64 @compute(i64 %x, i64 (i64)* %binop) {
+entry:
+  %tmp0 = call i64 %binop(i64 %x)
+  ret i64 %tmp0
+}
+
+define internal i64 @plus(i64 %x) {
+entry:
+  %tmp0 = add i64 %x, 1
+  ret i64 %tmp0
+}
+
+define internal i64 @minus(i64 %x) {
+entry:
+  %tmp0 = sub i64 %x, 1
+  ret i64 %tmp0
+}
+
+attributes #0 = { minsize optsize }