[llvm] r367011 - [InstCombine] try to narrow a truncated load
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Thu Jul 25 09:16:47 PDT 2019
Thanks! Any ideas about how to reproduce/reduce that failure?
On Thu, Jul 25, 2019 at 12:03 PM Vlad Tsyrklevich <vlad at tsyrklevich.net>
wrote:
> I've reverted this change as a speculative fix for second-stage
> miscompiles on a number of the sanitizer bots, e.g.
> http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap-ubsan/builds/14082 That
> bot seems to have recovered with the revert in place.
>
> On Thu, Jul 25, 2019 at 5:13 AM Sanjay Patel via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: spatel
>> Date: Thu Jul 25 05:14:27 2019
>> New Revision: 367011
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=367011&view=rev
>> Log:
>> [InstCombine] try to narrow a truncated load
>>
>> trunc (load X) --> load (bitcast X to narrow type)
>>
>> We have this transform in DAGCombiner::ReduceLoadWidth(), but the
>> truncated
>> load pattern can interfere with other instcombine transforms, so I'd like
>> to
>> allow the fold sooner.
>>
>> Example:
>> https://bugs.llvm.org/show_bug.cgi?id=16739
>> ...in that report, we have bitcasts bracketing these ops, so those could
>> get
>> eliminated too.
>>
>> We've generally ruled out widening of loads early in IR ( LoadCombine -
>> http://lists.llvm.org/pipermail/llvm-dev/2016-September/105291.html ),
>> but
>> that reasoning may not apply to narrowing if we can preserve information
>> such as the dereferenceable range.
>>
>> Differential Revision: https://reviews.llvm.org/D64432
>>
>> Modified:
>> llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
>> llvm/trunk/test/Transforms/InstCombine/trunc-load.ll
>>
>> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp?rev=367011&r1=367010&r2=367011&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp (original)
>> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp Thu Jul 25
>> 05:14:27 2019
>> @@ -681,6 +681,42 @@ static Instruction *shrinkInsertElt(Cast
>> return nullptr;
>> }
>>
>> +static Instruction *narrowLoad(TruncInst &Trunc,
>> + InstCombiner::BuilderTy &Builder,
>> + const DataLayout &DL) {
>> + // Check the layout to ensure we are not creating an unsupported
>> operation.
>> + // TODO: Create a GEP to offset the load?
>> + if (!DL.isLittleEndian())
>> + return nullptr;
>> + unsigned NarrowBitWidth = Trunc.getDestTy()->getPrimitiveSizeInBits();
>> + if (!DL.isLegalInteger(NarrowBitWidth))
>> + return nullptr;
>> +
>> + // Match a truncated load with no other uses.
>> + Value *X;
>> + if (!match(Trunc.getOperand(0), m_OneUse(m_Load(m_Value(X)))))
>> + return nullptr;
>> + LoadInst *WideLoad = cast<LoadInst>(Trunc.getOperand(0));
>> + if (!WideLoad->isSimple())
>> + return nullptr;
>> +
>> + // Don't narrow this load if we would lose information about the
>> + // dereferenceable range.
>> + bool CanBeNull;
>> + uint64_t DerefBits = X->getPointerDereferenceableBytes(DL, CanBeNull)
>> * 8;
>> + if (DerefBits < WideLoad->getType()->getPrimitiveSizeInBits())
>> + return nullptr;
>> +
>> + // trunc (load X) --> load (bitcast X)
>> + PointerType *PtrTy = PointerType::get(Trunc.getDestTy(),
>> +
>> WideLoad->getPointerAddressSpace());
>> + Value *Bitcast = Builder.CreatePointerCast(X, PtrTy);
>> + LoadInst *NarrowLoad = new LoadInst(Trunc.getDestTy(), Bitcast);
>> + NarrowLoad->setAlignment(WideLoad->getAlignment());
>> + copyMetadataForLoad(*NarrowLoad, *WideLoad);
>> + return NarrowLoad;
>> +}
>> +
>> Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
>> if (Instruction *Result = commonCastTransforms(CI))
>> return Result;
>> @@ -840,6 +876,9 @@ Instruction *InstCombiner::visitTrunc(Tr
>> if (Instruction *I = foldVecTruncToExtElt(CI, *this))
>> return I;
>>
>> + if (Instruction *NewLoad = narrowLoad(CI, Builder, DL))
>> + return NewLoad;
>> +
>> return nullptr;
>> }
>>
>>
>> Modified: llvm/trunk/test/Transforms/InstCombine/trunc-load.ll
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/trunc-load.ll?rev=367011&r1=367010&r2=367011&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/InstCombine/trunc-load.ll (original)
>> +++ llvm/trunk/test/Transforms/InstCombine/trunc-load.ll Thu Jul 25
>> 05:14:27 2019
>> @@ -29,10 +29,15 @@ define i32 @truncload_small_deref(i64* d
>> ; On little-endian, we can narrow the load without an offset.
>>
>> define i32 @truncload_deref(i64* dereferenceable(8) %ptr) {
>> -; CHECK-LABEL: @truncload_deref(
>> -; CHECK-NEXT: [[X:%.*]] = load i64, i64* [[PTR:%.*]], align 4
>> -; CHECK-NEXT: [[R:%.*]] = trunc i64 [[X]] to i32
>> -; CHECK-NEXT: ret i32 [[R]]
>> +; LE-LABEL: @truncload_deref(
>> +; LE-NEXT: [[TMP1:%.*]] = bitcast i64* [[PTR:%.*]] to i32*
>> +; LE-NEXT: [[R:%.*]] = load i32, i32* [[TMP1]], align 4
>> +; LE-NEXT: ret i32 [[R]]
>> +;
>> +; BE-LABEL: @truncload_deref(
>> +; BE-NEXT: [[X:%.*]] = load i64, i64* [[PTR:%.*]], align 4
>> +; BE-NEXT: [[R:%.*]] = trunc i64 [[X]] to i32
>> +; BE-NEXT: ret i32 [[R]]
>> ;
>> %x = load i64, i64* %ptr
>> %r = trunc i64 %x to i32
>> @@ -42,10 +47,15 @@ define i32 @truncload_deref(i64* derefer
>> ; Preserve alignment.
>>
>> define i16 @truncload_align(i32* dereferenceable(14) %ptr) {
>> -; CHECK-LABEL: @truncload_align(
>> -; CHECK-NEXT: [[X:%.*]] = load i32, i32* [[PTR:%.*]], align 16
>> -; CHECK-NEXT: [[R:%.*]] = trunc i32 [[X]] to i16
>> -; CHECK-NEXT: ret i16 [[R]]
>> +; LE-LABEL: @truncload_align(
>> +; LE-NEXT: [[TMP1:%.*]] = bitcast i32* [[PTR:%.*]] to i16*
>> +; LE-NEXT: [[R:%.*]] = load i16, i16* [[TMP1]], align 16
>> +; LE-NEXT: ret i16 [[R]]
>> +;
>> +; BE-LABEL: @truncload_align(
>> +; BE-NEXT: [[X:%.*]] = load i32, i32* [[PTR:%.*]], align 16
>> +; BE-NEXT: [[R:%.*]] = trunc i32 [[X]] to i16
>> +; BE-NEXT: ret i16 [[R]]
>> ;
>> %x = load i32, i32* %ptr, align 16
>> %r = trunc i32 %x to i16
>> @@ -98,12 +108,40 @@ define i32 @truncload_volatile(i64* dere
>> ; Preserve address space.
>>
>> define i32 @truncload_address_space(i64 addrspace(1)* dereferenceable(8)
>> %ptr) {
>> -; CHECK-LABEL: @truncload_address_space(
>> -; CHECK-NEXT: [[X:%.*]] = load i64, i64 addrspace(1)* [[PTR:%.*]],
>> align 4
>> -; CHECK-NEXT: [[R:%.*]] = trunc i64 [[X]] to i32
>> -; CHECK-NEXT: ret i32 [[R]]
>> +; LE-LABEL: @truncload_address_space(
>> +; LE-NEXT: [[TMP1:%.*]] = bitcast i64 addrspace(1)* [[PTR:%.*]] to
>> i32 addrspace(1)*
>> +; LE-NEXT: [[R:%.*]] = load i32, i32 addrspace(1)* [[TMP1]], align 4
>> +; LE-NEXT: ret i32 [[R]]
>> +;
>> +; BE-LABEL: @truncload_address_space(
>> +; BE-NEXT: [[X:%.*]] = load i64, i64 addrspace(1)* [[PTR:%.*]], align
>> 4
>> +; BE-NEXT: [[R:%.*]] = trunc i64 [[X]] to i32
>> +; BE-NEXT: ret i32 [[R]]
>> ;
>> %x = load i64, i64 addrspace(1)* %ptr, align 4
>> %r = trunc i64 %x to i32
>> ret i32 %r
>> }
>> +
>> +; Most metadata should be transferred to the narrow load.
>> +; TODO: We lost the range.
>> +
>> +define i32 @truncload_metadata(i64* dereferenceable(8) %ptr) {
>> +; LE-LABEL: @truncload_metadata(
>> +; LE-NEXT: [[TMP1:%.*]] = bitcast i64* [[PTR:%.*]] to i32*
>> +; LE-NEXT: [[R:%.*]] = load i32, i32* [[TMP1]], align 4,
>> !invariant.load !0, !nontemporal !1
>> +; LE-NEXT: ret i32 [[R]]
>> +;
>> +; BE-LABEL: @truncload_metadata(
>> +; BE-NEXT: [[X:%.*]] = load i64, i64* [[PTR:%.*]], align 4, !range
>> !0, !invariant.load !1, !nontemporal !2
>> +; BE-NEXT: [[R:%.*]] = trunc i64 [[X]] to i32
>> +; BE-NEXT: ret i32 [[R]]
>> +;
>> + %x = load i64, i64* %ptr, align 4, !invariant.load !0, !nontemporal
>> !1, !range !2
>> + %r = trunc i64 %x to i32
>> + ret i32 %r
>> +}
>> +
>> +!0 = !{}
>> +!1 = !{i32 1}
>> +!2 = !{i64 0, i64 2}
>>
>>
>> _______________________________________________
>> llvm-commits mailing list
>> llvm-commits at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20190725/82e6ebb7/attachment.html>
More information about the llvm-commits
mailing list