Make use of the align parameter attribute for all pointer arguments

We previously supported the align attribute on all (pointer) parameters, but we
only used it for byval parameters. However, it is completely consistent at the
IR level to treat 'align n' on all pointer parameters as an alignment
assumption on the pointer, and now we wll. Specifically, this causes
computeKnownBits to use the align attribute on all pointer parameters, not just
byval parameters. I've also added an explicit parameter attribute test for this
to test/Bitcode/attributes.ll.

And I've updated the LangRef to document the align parameter attribute (as it
turns out, it was not documented at all previously, although the byval
documentation mentioned that it could be used).

There are (at least) two benefits to doing this:
 - It allows enhancing alignment based on the pointer alignment after inlining callees.
 - It allows simplification of pointer arithmetic.

llvm-svn: 213670

1 files changed, 2 insertions, 6 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index e6d09f4..4edfb61 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -308,13 +308,9 @@ void llvm::computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
   }
 
   if (Argument *A = dyn_cast<Argument>(V)) {
-    unsigned Align = 0;
+    unsigned Align = A->getType()->isPointerTy() ? A->getParamAlignment() : 0;
 
-    if (A->hasByValOrInAllocaAttr()) {
-      // Get alignment information off byval/inalloca arguments if specified in
-      // the IR.
-      Align = A->getParamAlignment();
-    } else if (TD && A->hasStructRetAttr()) {
+    if (!Align && TD && A->hasStructRetAttr()) {
       // An sret parameter has at least the ABI alignment of the return type.
       Type *EltTy = cast<PointerType>(A->getType())->getElementType();
       if (EltTy->isSized())