[IR] Fix getPointerAlignment for CallBase

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.

Reviewers: jdoerfert

Reviewed By: jdoerfert

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65281

llvm-svn: 367185

llvm/lib/IR/Value.cpp

@@ -723,9 +723,11 @@ unsigned Value::getPointerAlignment(const DataLayout &DL) const {
       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();