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Introduce !align metadata for load instruction 

Reviewed By: hfinkel

Differential Revision: http://reviews.llvm.org/D12853

llvm-svn: 248721
This commit is contained in:
Artur Pilipenko 2015-09-28 17:41:08 +00:00
parent 8aba4b0589
commit b4d009042b
5 changed files with 29 additions and 2 deletions
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11
llvm/docs/LangRef.rst
View File

@ -6860,10 +6860,11 @@ Syntax:
::
<result> = load [volatile] <ty>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.load !<index>][, !invariant.group !<index>][, !nonnull !<index>][, !dereferenceable !<deref_bytes_node>][, !dereferenceable_or_null !<deref_bytes_node>]
<result> = load [volatile] <ty>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.load !<index>][, !invariant.group !<index>][, !nonnull !<index>][, !dereferenceable !<deref_bytes_node>][, !dereferenceable_or_null !<deref_bytes_node>][, !align !<align_node>]
<result> = load atomic [volatile] <ty>* <pointer> [singlethread] <ordering>, align <alignment> [, !invariant.group !<index>]
!<index> = !{ i32 1 }
!<deref_bytes_node> = !{i64 <dereferenceable_bytes>}
!<align_node> = !{ i64 <value_alignment> }
Overview:
"""""""""
@ -6948,6 +6949,14 @@ value in the metadata node. This is analogous to the ''dereferenceable_or_null''
attribute on parameters and return values. This metadata can only be applied
to loads of a pointer type.
The optional ``!align`` metadata must reference a single metadata name
``<align_node>`` corresponding to a metadata node with one ``i64`` entry.
The existence of the ``!align`` metadata on the instruction tells the
optimizer that the value loaded is known to be aligned to a boundary specified
by the integer value in the metadata node. The alignment must be a power of 2.
This is analogous to the ''align'' attribute on parameters and return values.
This metadata can only be applied to loads of a pointer type.
Semantics:
""""""""""

3
llvm/include/llvm/IR/LLVMContext.h
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@ -63,7 +63,8 @@ public:
MD_dereferenceable_or_null = 13, // "dereferenceable_or_null"
MD_make_implicit = 14, // "make.implicit"
MD_unpredictable = 15, // "unpredictable"
MD_invariant_group = 16 // "invariant.group"
MD_invariant_group = 16, // "invariant.group"
MD_align = 17 // "align"
};
/// getMDKindID - Return a unique non-zero ID for the specified metadata kind.

5
llvm/lib/Analysis/ValueTracking.cpp
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@ -2979,6 +2979,11 @@ static bool isAligned(const Value *Base, APInt Offset, unsigned Align,
BaseAlign = A->getParamAlignment();
else if (auto CS = ImmutableCallSite(Base))
BaseAlign = CS.getAttributes().getParamAlignment(AttributeSet::ReturnIndex);
else if (const LoadInst *LI = dyn_cast<LoadInst>(Base))
if (MDNode *MD = LI->getMetadata(LLVMContext::MD_align)) {
ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
BaseAlign = CI->getLimitedValue();
}
if (!BaseAlign) {
Type *Ty = Base->getType()->getPointerElementType();

4
llvm/lib/IR/LLVMContext.cpp
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@ -123,6 +123,10 @@ LLVMContext::LLVMContext() : pImpl(new LLVMContextImpl(*this)) {
"invariant.group kind id drifted");
(void)InvariantGroupId;
// Create the 'align' metadata kind.
unsigned AlignID = getMDKindID("align");
assert(AlignID == MD_align && "align kind id drifted");
(void)AlignID;
}
LLVMContext::~LLVMContext() { delete pImpl; }

8
llvm/test/Analysis/ValueTracking/memory-dereferenceable.ll
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@ -122,6 +122,14 @@ entry:
%load24 = load i32, i32* %deref_return, align 16
%load25 = load i32, i32* %deref_and_aligned_return, align 16
; Load from a dereferenceable and aligned load
; CHECK: %d4_unaligned_load{{.*}}(unaligned)
; CHECK: %d4_aligned_load{{.*}}(aligned)
%d4_unaligned_load = load i32*, i32** @globali32ptr, !dereferenceable !0
%d4_aligned_load = load i32*, i32** @globali32ptr, !dereferenceable !0, !align !{i64 16}
%load26 = load i32, i32* %d4_unaligned_load, align 16
%load27 = load i32, i32* %d4_aligned_load, align 16
ret void
}