[llvm] r213670 - Make use of the align parameter attribute for all pointer arguments

[Hal Finkel]

Author: hfinkel
Date: Tue Jul 22 11:58:55 2014
New Revision: 213670

URL: http://llvm.org/viewvc/llvm-project?rev=213670&view=rev
Log:
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.

Added:
    llvm/trunk/test/Transforms/InstCombine/align-attr.ll
Modified:
    llvm/trunk/docs/LangRef.rst
    llvm/trunk/lib/Analysis/ValueTracking.cpp
    llvm/trunk/test/Bitcode/attributes.ll

Modified: llvm/trunk/docs/LangRef.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/LangRef.rst?rev=213670&r1=213669&r2=213670&view=diff
==============================================================================
--- llvm/trunk/docs/LangRef.rst (original)
+++ llvm/trunk/docs/LangRef.rst Tue Jul 22 11:58:55 2014
@@ -921,6 +921,13 @@ Currently, only the following parameter
     the first parameter. This is not a valid attribute for return
     values.
 
+``align <n>``
+    This indicates that the pointer value may be assumed by the optimizer to
+    have the specified alignment.
+
+    Note that this attribute has additional semantics when combined with the
+    ``byval`` attribute.
+
 .. _noalias:
 
 ``noalias``

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=213670&r1=213669&r2=213670&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Tue Jul 22 11:58:55 2014
@@ -308,13 +308,9 @@ void llvm::computeKnownBits(Value *V, AP
   }
 
   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())

Modified: llvm/trunk/test/Bitcode/attributes.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Bitcode/attributes.ll?rev=213670&r1=213669&r2=213670&view=diff
==============================================================================
--- llvm/trunk/test/Bitcode/attributes.ll (original)
+++ llvm/trunk/test/Bitcode/attributes.ll Tue Jul 22 11:58:55 2014
@@ -239,6 +239,11 @@ define dereferenceable(18446744073709551
         ret i8* %a
 }
 
+define void @f41(i8* align 32, double* align 64) {
+; CHECK: define void @f41(i8* align 32, double* align 64) {
+        ret void
+}
+
 ; CHECK: attributes #0 = { noreturn }
 ; CHECK: attributes #1 = { nounwind }
 ; CHECK: attributes #2 = { readnone }

Added: llvm/trunk/test/Transforms/InstCombine/align-attr.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/align-attr.ll?rev=213670&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/align-attr.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/align-attr.ll Tue Jul 22 11:58:55 2014
@@ -0,0 +1,15 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: nounwind uwtable
+define i32 @foo1(i32* align 32 %a) #0 {
+entry:
+  %0 = load i32* %a, align 4
+  ret i32 %0
+
+; CHECK-LABEL: @foo1
+; CHECK-DAG: load i32* %a, align 32
+; CHECK: ret i32
+}
+