[llvm] r355921 - [SimplifyLibCalls] Simplify optimizePuts

[Fangrui Song via llvm-commits]

Author: maskray
Date: Tue Mar 12 07:20:22 2019
New Revision: 355921

URL: http://llvm.org/viewvc/llvm-project?rev=355921&view=rev
Log:
[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.

Modified:
    llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp

Modified: llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp?rev=355921&r1=355920&r2=355921&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp Tue Mar 12 07:20:22 2019
@@ -2387,18 +2387,14 @@ Value *LibCallSimplifier::optimizeFRead(
 }
 
 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;
 }