change instcombine to not turn a call to non-varargs bitcast of

function prototype into a call to a varargs prototype.  We do
allow the xform if we have a definition, but otherwise we don't
want to risk that we're changing the abi in a subtle way.  On
X86-64, for example, varargs require passing stuff in %al.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126363 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 15 insertions, 5 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineCalls.cpp b/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 8449f7b..0e46450 100644
--- a/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -953,10 +953,19 @@ bool InstCombiner::transformConstExprCastCall(CallSite CS) {
     if (Callee->isDeclaration() && !isConvertible) return false;
   }
 
-  if (FT->getNumParams() < NumActualArgs && !FT->isVarArg() &&
-      Callee->isDeclaration())
-    return false;   // Do not delete arguments unless we have a function body.
-
+  if (Callee->isDeclaration()) {
+    // Do not delete arguments unless we have a function body.
+    if (FT->getNumParams() < NumActualArgs && !FT->isVarArg())
+      return false;
+
+    // If the callee is just a declaration, don't change the varargsness of the
+    // call.  We don't want to introduce a varargs call where one doesn't
+    // already exist.
+    const PointerType *APTy = cast<PointerType>(CS.getCalledValue()->getType());
+    if (FT->isVarArg()!=cast<FunctionType>(APTy->getElementType())->isVarArg())
+      return false;
+  }
+      
   if (FT->getNumParams() < NumActualArgs && FT->isVarArg() &&
       !CallerPAL.isEmpty())
     // In this case we have more arguments than the new function type, but we
@@ -970,8 +979,9 @@ bool InstCombiner::transformConstExprCastCall(CallSite CS) {
         return false;
     }
 
+  
   // Okay, we decided that this is a safe thing to do: go ahead and start
-  // inserting cast instructions as necessary...
+  // inserting cast instructions as necessary.
   std::vector<Value*> Args;
   Args.reserve(NumActualArgs);
   SmallVector<AttributeWithIndex, 8> attrVec;