From b3b2aac5be89b327a5450affa743f2da2a906d7e Mon Sep 17 00:00:00 2001 From: Hal Finkel Date: Tue, 22 Jul 2014 16:58:55 +0000 Subject: [PATCH] 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. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213670 91177308-0d34-0410-b5e6-96231b3b80d8 --- docs/LangRef.rst | 7 +++++++ lib/Analysis/ValueTracking.cpp | 8 ++------ test/Bitcode/attributes.ll | 5 +++++ test/Transforms/InstCombine/align-attr.ll | 15 +++++++++++++++ 4 files changed, 29 insertions(+), 6 deletions(-) create mode 100644 test/Transforms/InstCombine/align-attr.ll diff --git a/docs/LangRef.rst b/docs/LangRef.rst index 867ef741da1..34873e1f41d 100644 --- a/docs/LangRef.rst +++ b/docs/LangRef.rst @@ -921,6 +921,13 @@ Currently, only the following parameter attributes are defined: the first parameter. This is not a valid attribute for return values. +``align `` + 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`` diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp index e6d09f4e31f..4edfb615f2a 100644 --- a/lib/Analysis/ValueTracking.cpp +++ b/lib/Analysis/ValueTracking.cpp @@ -308,13 +308,9 @@ void llvm::computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne, } if (Argument *A = dyn_cast(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(A->getType())->getElementType(); if (EltTy->isSized()) diff --git a/test/Bitcode/attributes.ll b/test/Bitcode/attributes.ll index 2490e592072..9a429f6e21f 100644 --- a/test/Bitcode/attributes.ll +++ b/test/Bitcode/attributes.ll @@ -239,6 +239,11 @@ define dereferenceable(18446744073709551606) i8* @f40(i8* dereferenceable(184467 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 } diff --git a/test/Transforms/InstCombine/align-attr.ll b/test/Transforms/InstCombine/align-attr.ll new file mode 100644 index 00000000000..9f366bf8fab --- /dev/null +++ b/test/Transforms/InstCombine/align-attr.ll @@ -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 +} + -- 2.34.1