[IR] Add bounds checking to paramHasAttr

Summary:
This is intended to make a later change simpler.

Note: adding this bounds checking required fixing `X86FastISel`.  As
far I can tell I've preserved original behavior but a careful review
will be appreciated.

Reviewers: reames

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D14304

llvm-svn: 252073

Author: sanjoy

llvm/lib/IR/Instructions.cpp

@@ -331,6 +331,8 @@ void CallInst::addDereferenceableOrNullAttr(unsigned i, uint64_t Bytes) {
 }
 
 bool CallInst::paramHasAttr(unsigned i, Attribute::AttrKind A) const {
+  assert(i < (getNumArgOperands() + 1) && "Param index out of bounds!");
+
   if (AttributeList.hasAttribute(i, A))
     return true;
   if (const Function *F = getCalledFunction())
@@ -575,6 +577,8 @@ bool InvokeInst::hasFnAttrImpl(Attribute::AttrKind A) const {
 }
 
 bool InvokeInst::paramHasAttr(unsigned i, Attribute::AttrKind A) const {
+  assert(i < (getNumArgOperands() + 1) && "Param index out of bounds!");
+
   if (AttributeList.hasAttribute(i, A))
     return true;
   if (const Function *F = getCalledFunction())

llvm/lib/Target/X86/X86FastISel.cpp

@@ -2817,10 +2817,12 @@ static unsigned computeBytesPoppedByCallee(const X86Subtarget *Subtarget,
   if (CC == CallingConv::Fast || CC == CallingConv::GHC ||
       CC == CallingConv::HiPE)
     return 0;
-  if (CS && !CS->paramHasAttr(1, Attribute::StructRet))
-    return 0;
-  if (CS && CS->paramHasAttr(1, Attribute::InReg))
-    return 0;
+
+  if (CS)
+    if (CS->arg_empty() || !CS->paramHasAttr(1, Attribute::StructRet) ||
+        CS->paramHasAttr(1, Attribute::InReg))
+      return 0;
+
   return 4;
 }