[stack protector] Make the StackProtector pass respect ssp-buffer-size.

Previously, SSPBufferSize was assigned the value of the "stack-protector-buffer-size"
attribute after all uses of SSPBufferSize.  The effect was that the default
SSPBufferSize was always used during analysis.  I moved the check for the
attribute before the analysis; now --param ssp-buffer-size= works correctly again.

Differential Revision: http://reviews.llvm.org/D3349

llvm-svn: 206486

llvm/lib/CodeGen/StackProtector.cpp

@@ -86,15 +86,15 @@ bool StackProtector::runOnFunction(Function &Fn) {
   DT = DTWP ? &DTWP->getDomTree() : nullptr;
   TLI = TM->getTargetLowering();
 
-  if (!RequiresStackProtector())
-    return false;
-
   Attribute Attr = Fn.getAttributes().getAttribute(
       AttributeSet::FunctionIndex, "stack-protector-buffer-size");
   if (Attr.isStringAttribute() &&
       Attr.getValueAsString().getAsInteger(10, SSPBufferSize))
       return false; // Invalid integer string
 
+  if (!RequiresStackProtector())
+    return false;
+
   ++NumFunProtected;
   return InsertStackProtectors();
 }