Only replace fwrite with fputc, if the return value is unused.

llvm-svn: 146411

Author: jsonn

llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp

@@ -1293,7 +1293,8 @@ struct FWriteOpt : public LibCallOptimization {
       return ConstantInt::get(CI->getType(), 0);
 
     // If this is writing one byte, turn it into fputc.
-    if (Bytes == 1) {  // fwrite(S,1,1,F) -> fputc(S[0],F)
+    // This optimisation is only valid, if the return value is unused.
+    if (Bytes == 1 && CI->use_empty()) {  // fwrite(S,1,1,F) -> fputc(S[0],F)
       Value *Char = B.CreateLoad(CastToCStr(CI->getArgOperand(0), B), "char");
       EmitFPutC(Char, CI->getArgOperand(3), B, TD);
       return ConstantInt::get(CI->getType(), 1);

llvm/test/Transforms/SimplifyLibCalls/fwrite.ll

@@ -0,0 +1,13 @@
+; RUN: opt < %s -simplify-libcalls -S | FileCheck %s
+
+%FILE = type { i32 }
+
+@.str = private unnamed_addr constant [1 x i8] zeroinitializer, align 1
+
+define i64 @foo(%FILE* %f) {
+; CHECK: %retval = call i64 @fwrite
+  %retval = call i64 @fwrite(i8* getelementptr inbounds ([1 x i8]* @.str, i64 0, i64 0), i64 1, i64 1, %FILE* %f)
+  ret i64 %retval
+}
+
+declare i64 @fwrite(i8*, i64, i64, %FILE *)