diff --git a/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp b/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
--- a/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
@@ -66,6 +66,12 @@
              "specialization"),
     cl::init(3));
 
+static cl::opt<unsigned> SmallFunctionThreshold(
+    "func-specialization-size-threshold", cl::Hidden,
+    cl::desc("For functions whose IR instruction count below this threshold, "
+             " they wouldn't be specialized to avoid useless sepcializations."),
+    cl::init(100));
+
 static cl::opt<unsigned>
     AvgLoopIterationCount("func-specialization-avg-iters-cost", cl::Hidden,
                           cl::desc("Average loop iteration count cost"),
@@ -340,6 +346,10 @@
     if (!Solver.isBlockExecutable(&F->getEntryBlock()))
       return false;
 
+    // It wastes time to specialize a function which would get inlined finally.
+    if (F->hasFnAttribute(Attribute::AlwaysInline))
+      return false;
+
     LLVM_DEBUG(dbgs() << "FnSpecialization: Try function: " << F->getName()
                       << "\n");
 
@@ -430,7 +440,11 @@
 
     // If the code metrics reveal that we shouldn't duplicate the function, we
     // shouldn't specialize it. Set the specialization cost to Invalid.
-    if (Metrics.notDuplicatable) {
+    // Or if the lines of codes implies that this function is easy to get
+    // inlined so that we shouldn't specialize it.
+    if (Metrics.notDuplicatable ||
+        (!ForceFunctionSpecialization &&
+         Metrics.NumInsts < SmallFunctionThreshold)) {
       InstructionCost C{};
       C.setInvalid();
       return C;
diff --git a/llvm/test/Transforms/FunctionSpecialization/function-specialization-loop.ll b/llvm/test/Transforms/FunctionSpecialization/function-specialization-always-inline.ll
copy from llvm/test/Transforms/FunctionSpecialization/function-specialization-loop.ll
copy to llvm/test/Transforms/FunctionSpecialization/function-specialization-always-inline.ll
--- a/llvm/test/Transforms/FunctionSpecialization/function-specialization-loop.ll
+++ b/llvm/test/Transforms/FunctionSpecialization/function-specialization-always-inline.ll
@@ -1,8 +1,6 @@
-; RUN: opt -function-specialization -func-specialization-avg-iters-cost=3 -S < %s | FileCheck %s
+; RUN: opt -function-specialization -func-specialization-avg-iters-cost=3 -func-specialization-size-threshold=10 -S < %s | FileCheck %s
 
-; Check that the loop depth results in a larger specialization bonus.
-; CHECK: @foo.1(
-; CHECK: @foo.2(
+; CHECK-NOT: foo.{{[0-9]+}}
 
 target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
 
@@ -15,7 +13,7 @@
 declare i1 @cond_end()
 declare i1 @getCond()
 
-define internal i32 @foo(i32 %x, i32* %b, i32* %c) {
+define internal i32 @foo(i32 %x, i32* %b, i32* %c) alwaysinline {
 entry:
   br label %loop.entry
 
diff --git a/llvm/test/Transforms/FunctionSpecialization/function-specialization-constant-integers.ll b/llvm/test/Transforms/FunctionSpecialization/function-specialization-constant-integers.ll
--- a/llvm/test/Transforms/FunctionSpecialization/function-specialization-constant-integers.ll
+++ b/llvm/test/Transforms/FunctionSpecialization/function-specialization-constant-integers.ll
@@ -1,4 +1,4 @@
-; RUN: opt -function-specialization -function-specialization-for-literal-constant=true -S < %s | FileCheck %s
+; RUN: opt -function-specialization -function-specialization-for-literal-constant=true -func-specialization-size-threshold=10 -S < %s | FileCheck %s
 
 ; Check that the literal constant parameter could be specialized.
 ; CHECK: @foo.1(
diff --git a/llvm/test/Transforms/FunctionSpecialization/function-specialization-loop.ll b/llvm/test/Transforms/FunctionSpecialization/function-specialization-loop.ll
--- a/llvm/test/Transforms/FunctionSpecialization/function-specialization-loop.ll
+++ b/llvm/test/Transforms/FunctionSpecialization/function-specialization-loop.ll
@@ -1,4 +1,4 @@
-; RUN: opt -function-specialization -func-specialization-avg-iters-cost=3 -S < %s | FileCheck %s
+; RUN: opt -function-specialization -func-specialization-avg-iters-cost=3 -func-specialization-size-threshold=10 -S < %s | FileCheck %s
 
 ; Check that the loop depth results in a larger specialization bonus.
 ; CHECK: @foo.1(
diff --git a/llvm/test/Transforms/FunctionSpecialization/function-specialization-stats.ll b/llvm/test/Transforms/FunctionSpecialization/function-specialization-stats.ll
--- a/llvm/test/Transforms/FunctionSpecialization/function-specialization-stats.ll
+++ b/llvm/test/Transforms/FunctionSpecialization/function-specialization-stats.ll
@@ -1,5 +1,5 @@
 ; REQUIRES: asserts
-; RUN: opt -stats -function-specialization -S < %s 2>&1 | FileCheck %s
+; RUN: opt -stats -function-specialization -S -force-function-specialization < %s 2>&1 | FileCheck %s
 
 ; CHECK: 2 function-specialization - Number of functions specialized
 
diff --git a/llvm/test/Transforms/FunctionSpecialization/function-specialization2.ll b/llvm/test/Transforms/FunctionSpecialization/function-specialization2.ll
--- a/llvm/test/Transforms/FunctionSpecialization/function-specialization2.ll
+++ b/llvm/test/Transforms/FunctionSpecialization/function-specialization2.ll
@@ -1,8 +1,8 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt -function-specialization -deadargelim -S < %s | FileCheck %s
-; RUN: opt -function-specialization -func-specialization-max-iters=1 -deadargelim -S < %s | FileCheck %s
-; RUN: opt -function-specialization -func-specialization-max-iters=0 -deadargelim -S < %s | FileCheck %s --check-prefix=DISABLED
-; RUN: opt -function-specialization -func-specialization-avg-iters-cost=1 -deadargelim -S < %s | FileCheck %s
+; RUN: opt -function-specialization -deadargelim -force-function-specialization -S < %s | FileCheck %s
+; RUN: opt -function-specialization -func-specialization-max-iters=1 -deadargelim -force-function-specialization -S < %s | FileCheck %s
+; RUN: opt -function-specialization -func-specialization-max-iters=0 -deadargelim -force-function-specialization -S < %s | FileCheck %s --check-prefix=DISABLED
+; RUN: opt -function-specialization -func-specialization-avg-iters-cost=1 -deadargelim -force-function-specialization -S < %s | FileCheck %s
 
 ; DISABLED-NOT: @func.1(
 ; DISABLED-NOT: @func.2(