[llvm] r367011 - [InstCombine] try to narrow a truncated load
Vlad Tsyrklevich via llvm-commits
llvm-commits at lists.llvm.org
Thu Jul 25 09:03:02 PDT 2019
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}
>
>
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