53401 Commits

Author SHA1 Message Date
Amara Emerson
2a312fc989 [AArch64][GlobalISel] RBS: Treat s128s like vectors when unmerging.
The destinations should be FPRs (for now).

Differential Revision: https://reviews.llvm.org/D66184

llvm-svn: 368775
2019-08-13 23:51:20 +00:00
Eli Friedman
b5eb3e1e82 [AArch64] Remove incorrect usage of MONonTemporal.
This has no effect at the moment, but might matter if we try to
implement non-temporal loads in the future.

llvm-svn: 368770
2019-08-13 23:12:14 +00:00
Xiangling Liao
a8c624a1c4 [AIX]Lowering global address for 32/64bit small/large code models
This patch implements global address lowering for 32/64 bit with small/large code models.
    1.For 32bit large code model on AIX, there are newly added pseudo opcode LWZtocL & ADDIStocHA32, the support of which on MC layer will be
       provided by future patches.
    2.The default code model on AIX should be small code model.
    3.Since AIX does not have medium code model, "report_fatal_error" when users specify it.

    Differential Revision: https://reviews.llvm.org/D63547

llvm-svn: 368744
2019-08-13 20:29:01 +00:00
Tim Renouf
10db641aab [AMDGPU] Fix to 'Fold readlane from copy of SGPR or imm'
That change (r363670) could leave a copy from vgpr to sgpr. Fixed.

Differential Revision: https://reviews.llvm.org/D66133

Change-Id: I00c3fe6fda2e8e1e36f53195b881b1449c777ea4
llvm-svn: 368736
2019-08-13 18:57:55 +00:00
David Green
a655393f17 [ARM] Add MVE beats vector cost model
The MVE architecture has the idea of "beats", where a vector instruction can be
executed over several ticks of the architecture. This adds a similar system
into the Arm backend cost model, multiplying the cost of all vector
instructions by a factor.

This factor essentially becomes the expected difference between scalar code
and vector code, on average. MVE Vector instructions can also overlap so the a
true cost of them is often lower. But equally scalar instructions can in some
situations be dual issued, or have other optimisations such as unrolling or
make use of dsp instructions. The default is chosen as 2. This should not
prevent vectorisation is a most cases (as the vector instructions will still be
doing at least 4 times the work), but it will help prevent over vectorising in
cases where the benefits are less likely.

This adds things so far to the obvious places in ARMTargetTransformInfo, and
updates a few related costs like not treating float instructions as cost 2 just
because they are floats.

Differential Revision: https://reviews.llvm.org/D66005

llvm-svn: 368733
2019-08-13 18:12:08 +00:00
Heejin Ahn
64517a6419 Use Register over unsigned in LateEHPrepare (NFC)
Summary:
While D65962 is pending for review, I landed D65475 that added one more
use of `unsigned`. Changed it to `Register`.

Reviewers: dsanders

Subscribers: dschuff, sbc100, jgravelle-google, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66064

llvm-svn: 368727
2019-08-13 17:35:44 +00:00
Hubert Tong
0996705009 Reland r368691: "[AIX] Implement LR prolog/epilog save/restore"
Trying again with the code changes (and not just the new test).

Summary:
This patch fixes the offsets of fields in the stack frame linkage save
area for AIX.

Reviewers: sfertile, hubert.reinterpretcast, jasonliu, Xiangling_L, xingxue, ZarkoCA, daltenty

Reviewed By: hubert.reinterpretcast

Subscribers: wuzish, nemanjai, hiraditya, kbarton, MaskRay, jsji, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64424

Patch by Chris Bowler!

llvm-svn: 368721
2019-08-13 17:05:53 +00:00
Matt Arsenault
28215caa60 GlobalISel: Partially implement fewerElementsVector G_UNMERGE_VALUES
Odd sized vectors aren't handled yet.

llvm-svn: 368713
2019-08-13 16:26:28 +00:00
Momchil Velikov
114c37e72a [ARM] Fix detection of duplicates when parsing reg list operands
Differential Revision: https://reviews.llvm.org/D65957

llvm-svn: 368712
2019-08-13 16:13:00 +00:00
Momchil Velikov
f990e4a4c7 [ARM] Fix encoding of APSR in CLRM instruction
The APSR is encoded by setting bit 15 in the register list of the CLRM
instruction (cf. https://static.docs.arm.com/ddi0553/bh/DDI0553B_h_armv8m_arm.pdf).

Differential Revision: https://reviews.llvm.org/D65873

llvm-svn: 368711
2019-08-13 16:12:46 +00:00
Matt Arsenault
690645bda0 GlobalISel: Implement lower for G_SHUFFLE_VECTOR
llvm-svn: 368709
2019-08-13 16:09:07 +00:00
Matt Arsenault
5af9cf042f GlobalISel: Change representation of shuffle masks
Currently shufflemasks get emitted as any other constant, and you end
up with a bunch of virtual registers of G_CONSTANT with a
G_BUILD_VECTOR. The AArch64 selector then asserts on anything that
doesn't fit this pattern. This isn't an ideal representation, and
should avoid legalization and have fewer opportunities for a
representational error.

Rather than invent a new shuffle mask operand type, similar to what
ShuffleVectorSDNode does, just track the original IR Constant mask
operand. I don't completely like the idea of adding another link to
the IR, but MIR is already quite dependent on IR constants already,
and this will allow sharing the shuffle mask utility functions with
the IR.

llvm-svn: 368704
2019-08-13 15:34:38 +00:00
Simon Pilgrim
e7b350a5d1 [X86] XFormVExtractWithShuffleIntoLoad - handle shuffle mask scaling
If the target shuffle mask is from a wider type, attempt to scale the mask so that the extraction can attempt to peek through.

Fixes the regression mentioned in rL368662

Reapplying this as rL368308 had to be reverted as part of rL368660 to revert rL368276

llvm-svn: 368663
2019-08-13 11:11:42 +00:00
Simon Pilgrim
1a8d790cf5 [X86] SimplifyDemandedVectorElts - attempt to recombine target shuffle using DemandedElts mask (reapplied)
If we don't demand all elements, then attempt to combine to a simpler shuffle.

At the moment we can only do this if Depth == 0 as combineX86ShufflesRecursively uses Depth to track whether the shuffle has really changed or not - we'll need to change this before we can properly start merging combineX86ShufflesRecursively into SimplifyDemandedVectorElts. 

The insertps-combine.ll regression is because XFormVExtractWithShuffleIntoLoad can't see through shuffles of different widths - this will be fixed in a follow-up commit.

Reapplying this as rL368307 had to be reverted as part of rL368660 to revert rL368276

llvm-svn: 368662
2019-08-13 10:51:39 +00:00
Hans Wennborg
5390d25f2b Revert r368276 "[TargetLowering] SimplifyDemandedBits - call SimplifyMultipleUseDemandedBits for ISD::EXTRACT_VECTOR_ELT"
This introduced a false positive MemorySanitizer warning about use of
uninitialized memory in a vectorized crc function in Chromium. That suggests
maybe something is not right with this transformation. See
https://crbug.com/992853#c7 for a reproducer.

This also reverts the follow-up commits r368307 and r368308 which
depended on this.

> This patch attempts to peek through vectors based on the demanded bits/elt of a particular ISD::EXTRACT_VECTOR_ELT node, allowing us to avoid dependencies on ops that have no impact on the extract.
>
> In particular this helps remove some unnecessary scalar->vector->scalar patterns.
>
> The wasm shift patterns are annoying - @tlively has indicated that the wasm vector shift codegen are to be refactored in the near-term and isn't considered a major issue.
>
> Differential Revision: https://reviews.llvm.org/D65887

llvm-svn: 368660
2019-08-13 09:33:25 +00:00
Qiu Chaofan
4fb99a3330 [PowerPC] Fix ICE when truncating some vectors
The legalizer would hit an assertion on PowerPC platform when truncating
a vector whose size is not power of 2.  This patch is to add a check to
prevent vectors with such odd-size elements from being custom lowered.

Reviewed By: Hal Finkel

Differential Revision: https://reviews.llvm.org/D65261

llvm-svn: 368654
2019-08-13 07:53:29 +00:00
Amara Emerson
72c81b94cb [AArch64][GlobalISel] Replace explicit vreg creation with implicit using SrcOp. NFC.
llvm-svn: 368653
2019-08-13 06:55:32 +00:00
Amara Emerson
e14c91b71a [GlobalISel] Make the InstructionSelector instance non-const, allowing state to be maintained.
Currently we can't keep any state in the selector object that we get from
subtarget. As a result we have to plumb through all our variables through
multiple functions. This change makes it non-const and adds a virtual init()
method to allow further state to be captured for each target.

AArch64 makes use of this in this patch to cache a call to hasFnAttribute()
which is expensive to call, and is used on each selection of G_BRCOND.

Differential Revision: https://reviews.llvm.org/D65984

llvm-svn: 368652
2019-08-13 06:26:59 +00:00
Stanislav Mekhanoshin
438315bf69 [AMDGPU] Fix msan failure in printf lowering
llvm-svn: 368645
2019-08-13 01:07:27 +00:00
Stanislav Mekhanoshin
5b32752d10 [AMDGPU] removed unused functions from printf lowering
Differential Revision: https://reviews.llvm.org/D66117

llvm-svn: 368633
2019-08-12 23:32:35 +00:00
Reid Kleckner
e9865b9b31 [WinEH] Fix catch block parent frame pointer offset
r367088 made it so that funclets store XMM registers into their local
frame instead of storing them to the parent frame. However, that change
forgot to update the parent frame pointer offset for catch blocks. This
change does that.

Fixes crashes when an exception is rethrown in a catch block that saves
XMMs, as described in https://crbug.com/992860.

llvm-svn: 368631
2019-08-12 23:02:00 +00:00
Daniel Sanders
3836874dbb [risc-v] Apply llvm-prefer-register-over-unsigned from clang-tidy to LLVM
Summary:
This clang-tidy check is looking for unsigned integer variables whose initializer
starts with an implicit cast from llvm::Register and changes the type of the
variable to llvm::Register (dropping the llvm:: where possible).

Depends on D65919

Reviewers: lenary

Subscribers: jholewinski, MatzeB, qcolombet, dschuff, jyknight, dylanmckay, sdardis, nemanjai, jvesely, wdng, nhaehnle, sbc100, jgravelle-google, kristof.beyls, hiraditya, aheejin, kbarton, fedor.sergeev, javed.absar, asb, rbar, johnrusso, simoncook, apazos, sabuasal, niosHD, jrtc27, MaskRay, zzheng, edward-jones, atanasyan, rogfer01, MartinMosbeck, brucehoult, the_o, tpr, PkmX, jocewei, jsji, Petar.Avramovic, asbirlea, Jim, s.egerton, llvm-commits

Tags: #llvm

Differential Revision for full review was: https://reviews.llvm.org/D65962

llvm-svn: 368629
2019-08-12 22:41:02 +00:00
Daniel Sanders
5ae66e56cf [aarch64] Apply llvm-prefer-register-over-unsigned from clang-tidy to LLVM
Summary:
This clang-tidy check is looking for unsigned integer variables whose initializer
starts with an implicit cast from llvm::Register and changes the type of the
variable to llvm::Register (dropping the llvm:: where possible).

Manual fixups in:
AArch64InstrInfo.cpp - genFusedMultiply() now takes a Register* instead of unsigned*
AArch64LoadStoreOptimizer.cpp - Ternary operator was ambiguous between Register/MCRegister. Settled on Register

Depends on D65919

Reviewers: aemerson

Subscribers: jholewinski, MatzeB, qcolombet, dschuff, jyknight, dylanmckay, sdardis, nemanjai, jvesely, wdng, nhaehnle, sbc100, jgravelle-google, kristof.beyls, hiraditya, aheejin, kbarton, fedor.sergeev, javed.absar, asb, rbar, johnrusso, simoncook, apazos, sabuasal, niosHD, jrtc27, MaskRay, zzheng, edward-jones, atanasyan, rogfer01, MartinMosbeck, brucehoult, the_o, tpr, PkmX, jocewei, jsji, Petar.Avramovic, asbirlea, Jim, s.egerton, llvm-commits

Tags: #llvm

Differential Revision for full review was: https://reviews.llvm.org/D65962

llvm-svn: 368628
2019-08-12 22:40:53 +00:00
Daniel Sanders
05c145d694 [webassembly] Apply llvm-prefer-register-over-unsigned from clang-tidy to LLVM
Summary:
This clang-tidy check is looking for unsigned integer variables whose initializer
starts with an implicit cast from llvm::Register and changes the type of the
variable to llvm::Register (dropping the llvm:: where possible).

Reviewers: aheejin

Subscribers: jholewinski, MatzeB, qcolombet, dschuff, jyknight, dylanmckay, sdardis, nemanjai, jvesely, wdng, nhaehnle, sbc100, jgravelle-google, kristof.beyls, hiraditya, aheejin, kbarton, fedor.sergeev, javed.absar, asb, rbar, johnrusso, simoncook, apazos, sabuasal, niosHD, jrtc27, MaskRay, zzheng, edward-jones, atanasyan, rogfer01, MartinMosbeck, brucehoult, the_o, tpr, PkmX, jocewei, jsji, Petar.Avramovic, asbirlea, Jim, s.egerton, llvm-commits

Tags: #llvm

Differential Revision for whole review: https://reviews.llvm.org/D65962

llvm-svn: 368627
2019-08-12 22:40:45 +00:00
Stanislav Mekhanoshin
ef8f1c473a [AMDGPU] Use PredicateControl in MIMGBaseOpcode. NFC.
This is infrastructural, will be needed for future work.
For some reason it was only used in MIMG_NoSampler, while
needed everywere we use MIMGBaseOpcode if we want to use
predicates.

Differential Revision: https://reviews.llvm.org/D66115

llvm-svn: 368626
2019-08-12 22:32:21 +00:00
Craig Topper
e07e593782 [X86] Allow combineTruncateWithSat to use pack instructions for i16->i8 without AVX512BW.
We need AVX512BW to be able to truncate an i16 vector. If we don't
have that we have to extend i16->i32, then trunc, i32->i8. But we
won't be able to remove the min/max if we do that. At least not
without more special handling.

llvm-svn: 368623
2019-08-12 22:18:23 +00:00
Craig Topper
0761a38e8a [X86] Remove unreachable code from LowerTRUNCATE. NFC
All three 256->128 bit cases were already handled above.

Noticed while looking at the coverage report.

llvm-svn: 368609
2019-08-12 19:26:45 +00:00
Craig Topper
a3605baaff [X86] Add a paranoia type check to the code that detects AVG patterns from truncating stores.
If we're after type legalize, we should make sure we won't create
a store with an illegal type when we separate the AVG pattern
from the truncating store.

I don't know of a way to fail for this today. Just noticed while
I was in the vicinity.

llvm-svn: 368608
2019-08-12 19:26:37 +00:00
Craig Topper
1b02909847 [X86] Simplify creation of saturating truncating stores.
We just need to check if the truncating store is legal
instead of going through isSATValidOnAVX512Subtarget.

llvm-svn: 368607
2019-08-12 19:26:30 +00:00
Craig Topper
3f4e9b156d [X86] Replace call to isTruncStoreLegalOrCustom with isTruncStoreLegal. NFC
We have no custom trunc stores on X86.

llvm-svn: 368606
2019-08-12 19:26:22 +00:00
Craig Topper
09d5d15339 [X86] Disable use of zmm registers for varargs musttail calls under prefer-vector-width=256 and min-legal-vector-width=256.
Under this config, the v16f32 type we try to use isn't to a register
class so the getRegClassFor call will fail.

llvm-svn: 368594
2019-08-12 17:43:26 +00:00
David Green
86876422ef [ARM] sext of a load is free
This teaches the cost model that the sext or zext of a load is going to be
free.

Differential Revision: https://reviews.llvm.org/D66006

llvm-svn: 368593
2019-08-12 17:39:56 +00:00
Stanislav Mekhanoshin
4c9c98f36b [AMDGPU] Printf runtime binding pass
This pass is a port of the according pass from the HSAIL compiler.
It parses printf calls and setup runtime printf buffer.
After that it copies printf arguments to the buffer and fills in
module metadata for runtime.

Differential Revision: https://reviews.llvm.org/D24035

llvm-svn: 368592
2019-08-12 17:12:29 +00:00
David Green
3e39f39ad9 [ARM] MVE shuffle broadcast costs
A VDUP will perform a vector broadcast in a single instruction. Update the cost
model for MVE accordingly.

Code originally by David Sherwood.

Differential Revision: https://reviews.llvm.org/D63448

llvm-svn: 368589
2019-08-12 16:54:07 +00:00
David Green
83bbfaa5e4 [ARM] Put some of the TTI costmodel behind hasNeon calls.
This puts some of the calls in ARMTargetTransformInfo.cpp behind hasNeon()
checks, now that we have MVE, and updates all the tests accordingly.

Differential Revision: https://reviews.llvm.org/D63447

llvm-svn: 368587
2019-08-12 15:59:52 +00:00
Sam Elliott
fee242aed4 [RISCV] Fix ICE in isDesirableToCommuteWithShift
Summary:
Ana Pazos reported a bug where we were not checking that an APInt would
fit into 64-bits before calling `getSExtValue()`. This caused asserts when
compiling large constants, such as i128s, as happens when compiling compiler-rt.

This patch adds a testcase and makes the callback less error-prone.

Reviewers: apazos, asb, luismarques

Reviewed By: luismarques

Subscribers: hiraditya, rbar, johnrusso, simoncook, sabuasal, niosHD, kito-cheng, shiva0217, jrtc27, MaskRay, zzheng, edward-jones, rogfer01, MartinMosbeck, brucehoult, the_o, rkruppe, PkmX, jocewei, psnobl, benna, Jim, s.egerton, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66081

llvm-svn: 368572
2019-08-12 13:51:00 +00:00
Simon Pilgrim
182249daee [X86][SSE] ComputeKnownBits - add basic PSADBW handling
llvm-svn: 368558
2019-08-12 12:19:19 +00:00
Pengfei Wang
e28cbbd5d4 [X86] Support -march=tigerlake
Support -march=tigerlake for x86.
Compare with Icelake Client, It include 4 more new features ,they are
avx512vp2intersect, movdiri, movdir64b, shstk.

Patch by Xiang Zhang (xiangzhangllvm)

Differential Revision: https://reviews.llvm.org/D65840

llvm-svn: 368543
2019-08-12 01:29:46 +00:00
Craig Topper
ce6a2cf966 [X86] Simplify some of the type checks in combineSubToSubus.
If we have SSE2 we can handle any i8/i16 type and let
type legalization deal with it.

llvm-svn: 368538
2019-08-11 17:36:49 +00:00
Craig Topper
637964bfd8 [X86] Don't use SplitOpsAndApply for ISD::USUBSAT.
Target independent type legalization and custom lowering
should be able to handle it.

llvm-svn: 368537
2019-08-11 17:36:45 +00:00
David Green
11c4602fce [MVE] Don't try to unroll vectorised MVE loops
Due to the nature of the beat system in the MVE architecture, along with tail
predication and low-overhead loops, unrolling has less benefit compared to
normal loops. You can not, for example, hide the latency of a load with other
instructions as you can for scalar code. Preventing unrolling also makes the
code easier to read and reason about.

So if a loop contains vector code, don't enable the runtime unrolling. At least
for the time being.

Differential Revision: https://reviews.llvm.org/D65803

llvm-svn: 368530
2019-08-11 08:53:18 +00:00
David Green
44f8d635e2 [ARM] Permit auto-vectorization using MVE
With enough codegen complete, we can now correctly report the number and size
of vector registers for MVE, allowing auto vectorisation. This also allows FP
auto-vectorization for MVE without -Ofast/-ffast-math, due to support for IEEE
FP arithmetic and parity between scalar and vector FP behaviour.

Patch by David Sherwood.

Differential Revision: https://reviews.llvm.org/D63728

llvm-svn: 368529
2019-08-11 08:42:57 +00:00
Heejin Ahn
831efe0e0f Fix __clang_call_termiante's argument for foreign exceptions
Summary:
When exceptions are repeatedly thrown in the middle of handling another
exception, we call `__clang_call_terminate` with the exception pointer
(i32) as an argument. But in case of foreign exceptions, we don't have
the pointer, so we call the function with 0. (This requires
`__clang_call_terminate` can deal with 0 argument, which will be done
later)

But previously the 0 argument was not added as a `i32.const 0` but an
immediate by mistake, causing the `call` instruction to take not an i32
but rather an exnref, because an `exnref` is left on top of the value
stack if `br_on_exn` is not taken.

```
block i32
  br_on_exn 0, __cpp_exception
                               ;; exnref is on top of stack now
  i32.const 0                  ;; This was missing!
  call __clang_call_terminate
  unreachable
end
call __clang_call_terminate    ;; This takes i32 extracted by br_on_exn
```

Reviewers: dschuff

Subscribers: sbc100, jgravelle-google, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65475

llvm-svn: 368527
2019-08-11 06:24:07 +00:00
Craig Topper
9758e0e1bf [X86] Remove some more code from combineShuffle that is no longer needed with widening legalization.
llvm-svn: 368523
2019-08-11 02:17:18 +00:00
Craig Topper
0f74b82ef1 [X86] Remove some code from combineShuffle that seems largely unnecessary with widening legalization.
The test case that changed is probably better served through
allowing combineTruncatedArithmetic to create narrow vectors. It
also appears InstCombine would have simplified this test case
to remove the zext and trunc anyway.

llvm-svn: 368522
2019-08-11 02:08:38 +00:00
Simon Pilgrim
ec128709f0 [X86][SSE] Lower shuffle as ANY_EXTEND_VECTOR_INREG
On SSE41+ targets we always lower vector shuffles to ZERO_EXTEND_VECTOR_INREG, even if we don't need the extended bits.

This patch relaxes this so that we lower to ANY_EXTEND_VECTOR_INREG if we can, meaning that shuffle combines have a better idea of what elements need to be kept zero. This helps the multiple reduction code as we can now combine away a lot more of the pack+extend codes.

Differential Revision: https://reviews.llvm.org/D65741

llvm-svn: 368515
2019-08-10 16:46:07 +00:00
Craig Topper
74c43a2277 [X86] Match the IR pattern form movmsk on SSE1 only targets where v4i32 isn't legal
Summary:
This patch adds a special DAG combine for SSE1 to recognize the IR pattern InstCombine gives us for movmsk. This only does the recognition for a few cases where its obvious the input won't be scalarized resulting in building a vector just do to the movmsk. I've made it separate from our existing matching for movmsk since that's called in multiple places and I didn't spend time to see if the other callers would make sense here. Plus the restrictions and additional checks would complicate that.

This fixes the case from PR42870. Buts its probably still broken the presence of logic ops feeding the movmsk pattern which would further hide the v4f32 type.

Reviewers: spatel, RKSimon, xbolva00

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65689

llvm-svn: 368506
2019-08-10 07:51:13 +00:00
Craig Topper
a8e5e73711 [X86] Improve the diagnostic for larger than 4-bit immediate for vpermil2pd/ps. Only allow MCConstantExprs.
llvm-svn: 368505
2019-08-10 04:28:52 +00:00
Luo, Yuanke
c6c86f4f81 [X86] Fix stack probe issue on windows32.
Summary:
On windows if the frame size exceed 4096 bytes, compiler need to
generate a call to _alloca_probe. X86CallFrameOptimization pass
changes the reserved stack size and cause of stack probe function
not be inserted. This patch fix the issue by detecting the call
frame size, if the size exceed 4096 bytes, drop X86CallFrameOptimization.

Reviewers: craig.topper, wxiao3, annita.zhang, rnk, RKSimon

Reviewed By: rnk

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65923

llvm-svn: 368503
2019-08-10 02:49:02 +00:00
Daniel Sanders
e9a57c2b23 [globalisel] Add G_SEXT_INREG
Summary:
Targets often have instructions that can sign-extend certain cases faster
than the equivalent shift-left/arithmetic-shift-right. Such cases can be
identified by matching a shift-left/shift-right pair but there are some
issues with this in the context of combines. For example, suppose you can
sign-extend 8-bit up to 32-bit with a target extend instruction.
  %1:_(s32) = G_SHL %0:_(s32), i32 24 # (I've inlined the G_CONSTANT for brevity)
  %2:_(s32) = G_ASHR %1:_(s32), i32 24
  %3:_(s32) = G_ASHR %2:_(s32), i32 1
would reasonably combine to:
  %1:_(s32) = G_SHL %0:_(s32), i32 24
  %2:_(s32) = G_ASHR %1:_(s32), i32 25
which no longer matches the special case. If your shifts and extend are
equal cost, this would break even as a pair of shifts but if your shift is
more expensive than the extend then it's cheaper as:
  %2:_(s32) = G_SEXT_INREG %0:_(s32), i32 8
  %3:_(s32) = G_ASHR %2:_(s32), i32 1
It's possible to match the shift-pair in ISel and emit an extend and ashr.
However, this is far from the only way to break this shift pair and make
it hard to match the extends. Another example is that with the right
known-zeros, this:
  %1:_(s32) = G_SHL %0:_(s32), i32 24
  %2:_(s32) = G_ASHR %1:_(s32), i32 24
  %3:_(s32) = G_MUL %2:_(s32), i32 2
can become:
  %1:_(s32) = G_SHL %0:_(s32), i32 24
  %2:_(s32) = G_ASHR %1:_(s32), i32 23

All upstream targets have been configured to lower it to the current
G_SHL,G_ASHR pair but will likely want to make it legal in some cases to
handle their faster cases.

To follow-up: Provide a way to legalize based on the constant. At the
moment, I'm thinking that the best way to achieve this is to provide the
MI in LegalityQuery but that opens the door to breaking core principles
of the legalizer (legality is not context sensitive). That said, it's
worth noting that looking at other instructions and acting on that
information doesn't violate this principle in itself. It's only a
violation if, at the end of legalization, a pass that checks legality
without being able to see the context would say an instruction might not be
legal. That's a fairly subtle distinction so to give a concrete example,
saying %2 in:
  %1 = G_CONSTANT 16
  %2 = G_SEXT_INREG %0, %1
is legal is in violation of that principle if the legality of %2 depends
on %1 being constant and/or being 16. However, legalizing to either:
  %2 = G_SEXT_INREG %0, 16
or:
  %1 = G_CONSTANT 16
  %2:_(s32) = G_SHL %0, %1
  %3:_(s32) = G_ASHR %2, %1
depending on whether %1 is constant and 16 does not violate that principle
since both outputs are genuinely legal.

Reviewers: bogner, aditya_nandakumar, volkan, aemerson, paquette, arsenm

Subscribers: sdardis, jvesely, wdng, nhaehnle, rovka, kristof.beyls, javed.absar, hiraditya, jrtc27, atanasyan, Petar.Avramovic, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D61289

llvm-svn: 368487
2019-08-09 21:11:20 +00:00