From: Fangrui Song <maskray@google.com>
Date: Tue, 12 Mar 2019 14:20:22 +0000 (+0000)
Subject: [SimplifyLibCalls] Simplify optimizePuts
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=e499a1a918172182029d280a544234aba8240634;p=llvm

[SimplifyLibCalls] Simplify optimizePuts

The code might intend to replace puts("") with putchar('\n') even if the
return value is used. It failed because use_empty() was used to guard
the whole block. While returning '\n' (putchar('\n')) is technically
correct (puts is only required to return a nonnegative number on
success), doing this looks weird and there is really little benefit to
optimize puts whose return value is used. So don't do that.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@355921 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Utils/SimplifyLibCalls.cpp b/lib/Transforms/Utils/SimplifyLibCalls.cpp
index b8a18a10f29..3920736a8d5 100644
--- a/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -2387,18 +2387,14 @@ Value *LibCallSimplifier::optimizeFRead(CallInst *CI, IRBuilder<> &B) {
 }
 
 Value *LibCallSimplifier::optimizePuts(CallInst *CI, IRBuilder<> &B) {
-  // Check for a constant string.
-  StringRef Str;
-  if (!getConstantStringInfo(CI->getArgOperand(0), Str))
+  if (!CI->use_empty())
     return nullptr;
 
-  if (Str.empty() && CI->use_empty()) {
-    // puts("") -> putchar('\n')
-    Value *Res = emitPutChar(B.getInt32('\n'), B, TLI);
-    if (CI->use_empty() || !Res)
-      return Res;
-    return B.CreateIntCast(Res, CI->getType(), true);
-  }
+  // Check for a constant string.
+  // puts("") -> putchar('\n')
+  StringRef Str;
+  if (getConstantStringInfo(CI->getArgOperand(0), Str) && Str.empty())
+    return emitPutChar(B.getInt32('\n'), B, TLI);
 
   return nullptr;
 }