From 45c41641664d8ff44c03f6205312d347081882b0 Mon Sep 17 00:00:00 2001
From: Joerg Sonnenberger <joerg@bec.de>
Date: Mon, 12 Dec 2011 20:18:31 +0000
Subject: [PATCH] Only replace fwrite with fputc, if the return value is
 unused.

llvm-svn: 146411
---
 llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp |  3 ++-
 llvm/test/Transforms/SimplifyLibCalls/fwrite.ll | 13 +++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/Transforms/SimplifyLibCalls/fwrite.ll

diff --git a/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp
index 075adc01873d..f3184ecc8601 100644
--- a/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp
+++ b/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);
diff --git a/llvm/test/Transforms/SimplifyLibCalls/fwrite.ll b/llvm/test/Transforms/SimplifyLibCalls/fwrite.ll
new file mode 100644
index 000000000000..f0f3dcaac63e
--- /dev/null
+++ b/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 *)
-- 
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