From d0eda03882633fe6c3160ea048b95369a8807567 Mon Sep 17 00:00:00 2001
From: Duncan Sands <baldrick@free.fr>
Date: Mon, 17 Aug 2009 14:33:27 +0000
Subject: [PATCH] Don't access the first element of a potentially empty vector
 (&Formals[0]).  With this change llvm-gcc builds with expensive checking
 enabled for C, C++ and Fortran. While there, change a std::vector into a
 SmallVector. This is partly gratuitous, but mostly because not all STL vector
 implementations define the data method (and it should be faster).

llvm-svn: 79237
---
 lib/Transforms/IPO/GlobalOpt.cpp | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/lib/Transforms/IPO/GlobalOpt.cpp b/lib/Transforms/IPO/GlobalOpt.cpp
index df49f7de81a..46ff307c755 100644
--- a/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/lib/Transforms/IPO/GlobalOpt.cpp
@@ -2156,7 +2156,7 @@ static Constant *ComputeLoadResult(Constant *P,
 /// successful, false if we can't evaluate it.  ActualArgs contains the formal
 /// arguments for the function.
 static bool EvaluateFunction(Function *F, Constant *&RetVal,
-                             const std::vector<Constant*> &ActualArgs,
+                             const SmallVectorImpl<Constant*> &ActualArgs,
                              std::vector<Function*> &CallStack,
                              DenseMap<Constant*, Constant*> &MutatedMemory,
                              std::vector<GlobalVariable*> &AllocaTmps) {
@@ -2251,14 +2251,14 @@ static bool EvaluateFunction(Function *F, Constant *&RetVal,
       Function *Callee = dyn_cast<Function>(getVal(Values, CI->getOperand(0)));
       if (!Callee) return false;  // Cannot resolve.
 
-      std::vector<Constant*> Formals;
+      SmallVector<Constant*, 8> Formals;
       for (User::op_iterator i = CI->op_begin() + 1, e = CI->op_end();
            i != e; ++i)
         Formals.push_back(getVal(Values, *i));
-      
+
       if (Callee->isDeclaration()) {
         // If this is a function we can constant fold, do it.
-        if (Constant *C = ConstantFoldCall(Callee, &Formals[0],
+        if (Constant *C = ConstantFoldCall(Callee, Formals.data(),
                                            Formals.size())) {
           InstResult = C;
         } else {
@@ -2353,8 +2353,9 @@ static bool EvaluateStaticConstructor(Function *F) {
 
   // Call the function.
   Constant *RetValDummy;
-  bool EvalSuccess = EvaluateFunction(F, RetValDummy, std::vector<Constant*>(),
-                                       CallStack, MutatedMemory, AllocaTmps);
+  bool EvalSuccess = EvaluateFunction(F, RetValDummy,
+                                      SmallVector<Constant*, 0>(), CallStack,
+                                      MutatedMemory, AllocaTmps);
   if (EvalSuccess) {
     // We succeeded at evaluation: commit the result.
     DEBUG(errs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"