[IR] Fix getPointerAlignment for CallBase

[uenoku]

Summary

In current getPointerAlignemnt implementation, CallBase.getPointerAlignement(..) checks only parameter attriutes in the callsite. For example,

declare align 8 i8* @foo()

define void @bar() {
    %a = tail call align 8 i8* @foo() ; getPointerAlignment returns 8
    %b = tail call i8* @foo() ; getPointerAlignemnt returns 0
    ret void
}

This patch will fix the problem.

[jdoerfert]

LGTM, looks straight forward

llvm/trunk/lib/IR/Value.cpp

if (auto *GO = dyn_cast<GlobalObject>(this)) {
     }
   } else if (const AllocaInst *AI = dyn_cast<AllocaInst>(this)) {
     Align = AI->getAlignment();
     if (Align == 0) {
       Type *AllocatedType = AI->getAllocatedType();
       if (AllocatedType->isSized())
         Align = DL.getPrefTypeAlignment(AllocatedType);
     }
-  } else if (const auto *Call = dyn_cast<CallBase>(this))
-    Align = Call->getAttributes().getRetAlignment();
-  else if (const LoadInst *LI = dyn_cast<LoadInst>(this))
+  } else if (const auto *Call = dyn_cast<CallBase>(this)) {
+    Align = Call->getRetAlignment();
+    if (Align == 0 && Call->getCalledFunction())
+      Align = Call->getCalledFunction()->getAttributes().getRetAlignment();
+  } else if (const LoadInst *LI = dyn_cast<LoadInst>(this))
     if (MDNode *MD = LI->getMetadata(LLVMContext::MD_align)) {
       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
       Align = CI->getLimitedValue();
     }
 
   return Align;
 }