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UPC-IR: typed runtime interface #4

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nenadv opened this issue Oct 13, 2014 · 2 comments
Closed

UPC-IR: typed runtime interface #4

nenadv opened this issue Oct 13, 2014 · 2 comments

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@nenadv
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nenadv commented Oct 13, 2014

At the beginning, I think the idea was to convert RP pointer into the UPC pointer before we call the runtime. This way we can have only one interface. But I see that this is not that useful as the interface is very simple and there is no point in generation the code of putting it back to the form fo rthe purpose of the AP only (we do not use phase in the runtime).

However, we can probably do better if instead of having the general get/put interface, we have it based on the type (i8, i16, i32, ....). This will minimize the possible inlined generated code for access routines (at least for the SMP runtime and on node accesses for p4/libfabric).

So, instead of:

upcr_llvm_getn ()

we would have

upcr_llvm_get_i8()
upcr_llvm_get_i16()
upcr_llvm_get_i32()
upcr_llvm_get_i64()
upcr_llvm_get_i128()
...
@swatanabe
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AMDG

On 10/13/2014 07:11 AM, Nenad Vukicevic wrote:

At the beginning, I think the idea was to convert RP pointer into the UPC pointer before we call the runtime. This way we can have only one interface. But I see that this is not that useful as the interface is very simple and there is no point in generation the code of putting it back to the form fo rthe purpose of the AP only (we do not use phase in the runtime).

However, we can probably do better if instead of having the general get/put interface, we have it based on the type (i8, i16, i32, ....). This will minimize the possible inlined generated code for access routines (at least for the SMP runtime and on node accesses for p4/libfabric).

So, instead of:

upcr_llvm_getn ()

we would have

upcr_llvm_get_i8()
upcr_llvm_get_i16()
upcr_llvm_get_i32()
upcr_llvm_get_i64()
upcr_llvm_get_i128()
...

Right. As far as naming conventions go,
I assume it should be get_float, get_double,
and get_pointer as well? Am I forgetting
anything?

In Christ,
Steven Watanabe

@nenadv
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nenadv commented Oct 16, 2014

On 10/15/14 6:17 PM, swatanabe wrote:

Right. As far as naming conventions go,
I assume it should be get_float, get_double,
and get_pointer as well? Am I forgetting
anything?

I think that we should have whatever LLVM types are. Make sense? I do
not recall having pointer type in the clang interface.

swatanabe added a commit that referenced this issue Dec 9, 2014
@swatanabe
Add separate access functions for specific types. Fixes #4.
ee3e600
@nenadv nenadv closed this as completed Dec 22, 2014
swatanabe pushed a commit that referenced this issue Mar 11, 2017
@zmodem
Merging r277625:
8820ca4 
------------------------------------------------------------------------
r277625 | dexonsmith | 2016-08-03 11:19:43 -0700 (Wed, 03 Aug 2016) | 42 lines

IR: Drop uniquing when an MDNode Value operand is deleted

This is a fix for PR28697.

An MDNode can indirectly refer to a GlobalValue, through a
ConstantAsMetadata.  When the GlobalValue is deleted, the MDNode operand
is reset to `nullptr`.  If the node is uniqued, this can lead to a
hard-to-detect cache invalidation in a Metadata map that's shared across
an LLVMContext.

Consider:

 1. A map from Metadata* to `T` called RemappedMDs.
 2. A node that references a global variable, `!{i1* @gv}`.
 3. Insert `!{i1* @gv} -> SomeT` in the map.
 4. Delete `@GV`, leaving behind `!{null} -> SomeT`.

Looking up the generic and uninteresting `!{null}` gives you `SomeT`,
which is likely related to `@GV`.  Worse, `SomeT`'s lifetime may be tied
to the deleted `@GV`.

This occurs in practice in the shared ValueMap used since r266579 in the
IRMover.  Other code that handles more than one Module (with different
lifetimes) in the same LLVMContext could hit it too.

The fix here is a partial revert of r225223: in the rare case that an
MDNode operand is a ConstantAsMetadata (i.e., wrapping a node from the
Value hierarchy), drop uniquing if it gets replaced with `nullptr`.
This changes step #4 above to leave behind `distinct !{null} -> SomeT`,
which can't be confused with the generic `!{null}`.

In theory, this can cause some churn in the LLVMContext's MDNode
uniquing map when Values are being deleted.  However:

  - The number of GlobalValues referenced from uniqued MDNodes is
    expected to be quite small.  E.g., the debug info metadata schema
    only references GlobalValues from distinct nodes.

  - Other Constants have the lifetime of the LLVMContext, whose teardown
    is careful to drop references before deleting the constants.

As a result, I don't expect a compile time regression from this change.
------------------------------------------------------------------------


git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_39@277639 91177308-0d34-0410-b5e6-96231b3b80d8
jleidel pushed a commit to tactcomplabs/llvm-upc that referenced this issue Oct 21, 2020
@yonghong-song
[BPF] add new intrinsics preserve_{array,union,struct}_access_index
35c568c 
For background of BPF CO-RE project, please refer to
  http://vger.kernel.org/bpfconf2019.html
In summary, BPF CO-RE intends to compile bpf programs
adjustable on struct/union layout change so the same
program can run on multiple kernels with adjustment
before loading based on native kernel structures.

In order to do this, we need keep track of GEP(getelementptr)
instruction base and result debuginfo types, so we
can adjust on the host based on kernel BTF info.
Capturing such information as an IR optimization is hard
as various optimization may have tweaked GEP and also
union is replaced by structure it is impossible to track
fieldindex for union member accesses.

Three intrinsic functions, preserve_{array,union,struct}_access_index,
are introducted.
  addr = preserve_array_access_index(base, index, dimension)
  addr = preserve_union_access_index(base, di_index)
  addr = preserve_struct_access_index(base, gep_index, di_index)
here,
  base: the base pointer for the array/union/struct access.
  index: the last access index for array, the same for IR/DebugInfo layout.
  dimension: the array dimension.
  gep_index: the access index based on IR layout.
  di_index: the access index based on user/debuginfo types.

For example, for the following example,
  $ cat test.c
  struct sk_buff {
     int i;
     int b1:1;
     int b2:2;
     union {
       struct {
         int o1;
         int o2;
       } o;
       struct {
         char flags;
         char dev_id;
       } dev;
       int netid;
     } u[10];
  };

  static int (*bpf_probe_read)(void *dst, int size, const void *unsafe_ptr)
      = (void *) 4;

  #define _(x) (__builtin_preserve_access_index(x))

  int bpf_prog(struct sk_buff *ctx) {
    char dev_id;
    bpf_probe_read(&dev_id, sizeof(char), _(&ctx->u[5].dev.dev_id));
    return dev_id;
  }
  $ clang -target bpf -O2 -g -emit-llvm -S -mllvm -print-before-all \
    test.c >& log

The generated IR looks like below:

  ...
  define dso_local i32 @bpf_prog(%struct.sk_buff*) #0 !dbg !15 {
    %2 = alloca %struct.sk_buff*, align 8
    %3 = alloca i8, align 1
    store %struct.sk_buff* %0, %struct.sk_buff** %2, align 8, !tbaa !45
    call void @llvm.dbg.declare(metadata %struct.sk_buff** %2, metadata !43, metadata !DIExpression()), !dbg !49
    call void @llvm.lifetime.start.p0i8(i64 1, i8* %3) clangupc#4, !dbg !50
    call void @llvm.dbg.declare(metadata i8* %3, metadata !44, metadata !DIExpression()), !dbg !51
    %4 = load i32 (i8*, i32, i8*)*, i32 (i8*, i32, i8*)** @bpf_probe_read, align 8, !dbg !52, !tbaa !45
    %5 = load %struct.sk_buff*, %struct.sk_buff** %2, align 8, !dbg !53, !tbaa !45
    %6 = call [10 x %union.anon]* @llvm.preserve.struct.access.index.p0a10s_union.anons.p0s_struct.sk_buffs(
         %struct.sk_buff* %5, i32 2, i32 3), !dbg !53, !llvm.preserve.access.index !19
    %7 = call %union.anon* @llvm.preserve.array.access.index.p0s_union.anons.p0a10s_union.anons(
         [10 x %union.anon]* %6, i32 1, i32 5), !dbg !53
    %8 = call %union.anon* @llvm.preserve.union.access.index.p0s_union.anons.p0s_union.anons(
         %union.anon* %7, i32 1), !dbg !53, !llvm.preserve.access.index !26
    %9 = bitcast %union.anon* %8 to %struct.anon.0*, !dbg !53
    %10 = call i8* @llvm.preserve.struct.access.index.p0i8.p0s_struct.anon.0s(
         %struct.anon.0* %9, i32 1, i32 1), !dbg !53, !llvm.preserve.access.index !34
    %11 = call i32 %4(i8* %3, i32 1, i8* %10), !dbg !52
    %12 = load i8, i8* %3, align 1, !dbg !54, !tbaa !55
    %13 = sext i8 %12 to i32, !dbg !54
    call void @llvm.lifetime.end.p0i8(i64 1, i8* %3) clangupc#4, !dbg !56
    ret i32 %13, !dbg !57
  }

  !19 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "sk_buff", file: !3, line: 1, size: 704, elements: !20)
  !26 = distinct !DICompositeType(tag: DW_TAG_union_type, scope: !19, file: !3, line: 5, size: 64, elements: !27)
  !34 = distinct !DICompositeType(tag: DW_TAG_structure_type, scope: !26, file: !3, line: 10, size: 16, elements: !35)

Note that @llvm.preserve.{struct,union}.access.index calls have metadata llvm.preserve.access.index
attached to instructions to provide struct/union debuginfo type information.

For &ctx->u[5].dev.dev_id,
  . The "%6 = ..." represents struct member "u" with index 2 for IR layout and index 3 for DI layout.
  . The "%7 = ..." represents array subscript "5".
  . The "%8 = ..." represents union member "dev" with index 1 for DI layout.
  . The "%10 = ..." represents struct member "dev_id" with index 1 for both IR and DI layout.

Basically, traversing the use-def chain recursively for the 3rd argument of bpf_probe_read() and
examining all preserve_*_access_index calls, the debuginfo struct/union/array access index
can be achieved.

The intrinsics also contain enough information to regenerate codes for IR layout.
For array and structure intrinsics, the proper GEP can be constructed.
For union intrinsics, replacing all uses of "addr" with "base" should be enough.

Signed-off-by: Yonghong Song <yhs@fb.com>

Differential Revision: https://reviews.llvm.org/D61810

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@365352 91177308-0d34-0410-b5e6-96231b3b80d8
jleidel pushed a commit to tactcomplabs/llvm-upc that referenced this issue Oct 21, 2020
@yonghong-song
[BPF] add new intrinsics preserve_{array,union,struct}_access_index
ccb54f3 
For background of BPF CO-RE project, please refer to
  http://vger.kernel.org/bpfconf2019.html
In summary, BPF CO-RE intends to compile bpf programs
adjustable on struct/union layout change so the same
program can run on multiple kernels with adjustment
before loading based on native kernel structures.

In order to do this, we need keep track of GEP(getelementptr)
instruction base and result debuginfo types, so we
can adjust on the host based on kernel BTF info.
Capturing such information as an IR optimization is hard
as various optimization may have tweaked GEP and also
union is replaced by structure it is impossible to track
fieldindex for union member accesses.

Three intrinsic functions, preserve_{array,union,struct}_access_index,
are introducted.
  addr = preserve_array_access_index(base, index, dimension)
  addr = preserve_union_access_index(base, di_index)
  addr = preserve_struct_access_index(base, gep_index, di_index)
here,
  base: the base pointer for the array/union/struct access.
  index: the last access index for array, the same for IR/DebugInfo layout.
  dimension: the array dimension.
  gep_index: the access index based on IR layout.
  di_index: the access index based on user/debuginfo types.

For example, for the following example,
  $ cat test.c
  struct sk_buff {
     int i;
     int b1:1;
     int b2:2;
     union {
       struct {
         int o1;
         int o2;
       } o;
       struct {
         char flags;
         char dev_id;
       } dev;
       int netid;
     } u[10];
  };

  static int (*bpf_probe_read)(void *dst, int size, const void *unsafe_ptr)
      = (void *) 4;

  #define _(x) (__builtin_preserve_access_index(x))

  int bpf_prog(struct sk_buff *ctx) {
    char dev_id;
    bpf_probe_read(&dev_id, sizeof(char), _(&ctx->u[5].dev.dev_id));
    return dev_id;
  }
  $ clang -target bpf -O2 -g -emit-llvm -S -mllvm -print-before-all \
    test.c >& log

The generated IR looks like below:

  ...
  define dso_local i32 @bpf_prog(%struct.sk_buff*) #0 !dbg !15 {
    %2 = alloca %struct.sk_buff*, align 8
    %3 = alloca i8, align 1
    store %struct.sk_buff* %0, %struct.sk_buff** %2, align 8, !tbaa !45
    call void @llvm.dbg.declare(metadata %struct.sk_buff** %2, metadata !43, metadata !DIExpression()), !dbg !49
    call void @llvm.lifetime.start.p0i8(i64 1, i8* %3) clangupc#4, !dbg !50
    call void @llvm.dbg.declare(metadata i8* %3, metadata !44, metadata !DIExpression()), !dbg !51
    %4 = load i32 (i8*, i32, i8*)*, i32 (i8*, i32, i8*)** @bpf_probe_read, align 8, !dbg !52, !tbaa !45
    %5 = load %struct.sk_buff*, %struct.sk_buff** %2, align 8, !dbg !53, !tbaa !45
    %6 = call [10 x %union.anon]* @llvm.preserve.struct.access.index.p0a10s_union.anons.p0s_struct.sk_buffs(
         %struct.sk_buff* %5, i32 2, i32 3), !dbg !53, !llvm.preserve.access.index !19
    %7 = call %union.anon* @llvm.preserve.array.access.index.p0s_union.anons.p0a10s_union.anons(
         [10 x %union.anon]* %6, i32 1, i32 5), !dbg !53
    %8 = call %union.anon* @llvm.preserve.union.access.index.p0s_union.anons.p0s_union.anons(
         %union.anon* %7, i32 1), !dbg !53, !llvm.preserve.access.index !26
    %9 = bitcast %union.anon* %8 to %struct.anon.0*, !dbg !53
    %10 = call i8* @llvm.preserve.struct.access.index.p0i8.p0s_struct.anon.0s(
         %struct.anon.0* %9, i32 1, i32 1), !dbg !53, !llvm.preserve.access.index !34
    %11 = call i32 %4(i8* %3, i32 1, i8* %10), !dbg !52
    %12 = load i8, i8* %3, align 1, !dbg !54, !tbaa !55
    %13 = sext i8 %12 to i32, !dbg !54
    call void @llvm.lifetime.end.p0i8(i64 1, i8* %3) clangupc#4, !dbg !56
    ret i32 %13, !dbg !57
  }

  !19 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "sk_buff", file: !3, line: 1, size: 704, elements: !20)
  !26 = distinct !DICompositeType(tag: DW_TAG_union_type, scope: !19, file: !3, line: 5, size: 64, elements: !27)
  !34 = distinct !DICompositeType(tag: DW_TAG_structure_type, scope: !26, file: !3, line: 10, size: 16, elements: !35)

Note that @llvm.preserve.{struct,union}.access.index calls have metadata llvm.preserve.access.index
attached to instructions to provide struct/union debuginfo type information.

For &ctx->u[5].dev.dev_id,
  . The "%6 = ..." represents struct member "u" with index 2 for IR layout and index 3 for DI layout.
  . The "%7 = ..." represents array subscript "5".
  . The "%8 = ..." represents union member "dev" with index 1 for DI layout.
  . The "%10 = ..." represents struct member "dev_id" with index 1 for both IR and DI layout.

Basically, traversing the use-def chain recursively for the 3rd argument of bpf_probe_read() and
examining all preserve_*_access_index calls, the debuginfo struct/union/array access index
can be achieved.

The intrinsics also contain enough information to regenerate codes for IR layout.
For array and structure intrinsics, the proper GEP can be constructed.
For union intrinsics, replacing all uses of "addr" with "base" should be enough.

The test case ThinLTO/X86/lazyload_metadata.ll is adjusted to reflect the
new addition of the metadata.

Signed-off-by: Yonghong Song <yhs@fb.com>

Differential Revision: https://reviews.llvm.org/D61810

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@365423 91177308-0d34-0410-b5e6-96231b3b80d8
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@swatanabe @nenadv