Index: lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -2056,6 +2056,8 @@
     case LibFunc::fwrite:
       return optimizeFWrite(CI, Builder);
     case LibFunc::fputs:
+      if (CI->getParent()->getParent()->optForSize())
+        return nullptr;
       return optimizeFPuts(CI, Builder);
     case LibFunc::log:
     case LibFunc::log10:
Index: test/Transforms/InstCombine/fputs-opt-size.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/fputs-opt-size.ll
@@ -0,0 +1,28 @@
+; When optimising for size, we don't want to rewrite fputs to fwrite
+; because it requires more arguments and thus extra MOVs are required.
+;
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+%struct._IO_FILE = type { i32, i8*, i8*, i8*, i8*, i8*, i8*, i8*, i8*, i8*, i8*, i8*, %struct._IO_marker*, %struct._IO_FILE*, i32, i32, i32, i16, i8, [1 x i8], i8*, i64, i8*, i8*, i8*, i8*, i32, i32, [40 x i8] }
+%struct._IO_marker = type { %struct._IO_marker*, %struct._IO_FILE*, i32 }
+
+@.str = private unnamed_addr constant [10 x i8] c"mylog.txt\00", align 1
+@.str.1 = private unnamed_addr constant [2 x i8] c"a\00", align 1
+@.str.2 = private unnamed_addr constant [27 x i8] c"Hello world this is a test\00", align 1
+
+define i32 @main() local_unnamed_addr #0 {
+entry:
+; CHECK-LABEL: @main(
+; CHECK-NOT: call i64 @fwrite
+; CHECK: call i32 @fputs
+
+  %call = tail call %struct._IO_FILE* @fopen(i8* getelementptr inbounds ([10 x i8], [10 x i8]* @.str, i32 0, i32 0), i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.str.1, i32 0, i32 0)) #2
+  %call1 = tail call i32 @fputs(i8* getelementptr inbounds ([27 x i8], [27 x i8]* @.str.2, i32 0, i32 0), %struct._IO_FILE* %call) #2
+  ret i32 0
+}
+
+declare noalias %struct._IO_FILE* @fopen(i8* nocapture readonly, i8* nocapture readonly) local_unnamed_addr #1
+declare i32 @fputs(i8* nocapture readonly, %struct._IO_FILE* nocapture) local_unnamed_addr #1
+
+attributes #0 = { nounwind optsize }
+attributes #1 = { nounwind optsize  }