[all-commits] [llvm/llvm-project] 3568d6: BPF: Implement TTI.IntImmCost() properly

[yonghong-song via All-commits]

  Branch: refs/heads/release/12.x
  Home:   https://github.com/llvm/llvm-project
  Commit: 3568d61f11e2eb0017c7b65707bee7bf4111c8ca
      https://github.com/llvm/llvm-project/commit/3568d61f11e2eb0017c7b65707bee7bf4111c8ca
  Author: Yonghong Song <yhs at fb.com>
  Date:   2021-05-03 (Mon, 03 May 2021)

  Changed paths:
    M llvm/lib/Target/BPF/BPFTargetMachine.cpp
    M llvm/lib/Target/BPF/BPFTargetMachine.h
    A llvm/lib/Target/BPF/BPFTargetTransformInfo.h

  Log Message:
  -----------
  BPF: Implement TTI.IntImmCost() properly

This patch implemented TTI.IntImmCost() properly.
Each BPF insn has 32bit immediate space, so for any immediate
which can be represented as 32bit signed int, the cost
is technically free. If an int cannot be presented as
a 32bit signed int, a ld_imm64 instruction is needed
and a TCC_Basic is returned.

This change is motivated when we observed that
several bpf selftests failed with latest llvm trunk, e.g.,
  #10/16 strobemeta.o:FAIL
  #10/17 strobemeta_nounroll1.o:FAIL
  #10/18 strobemeta_nounroll2.o:FAIL
  #10/19 strobemeta_subprogs.o:FAIL
  #96 snprintf_btf:FAIL

The reason of the failure is due to that
SpeculateAroundPHIsPass did aggressive transformation
which alters control flow for which currently verifer
cannot handle well. In llvm12, SpeculateAroundPHIsPass
is not called.

SpeculateAroundPHIsPass relied on TTI.getIntImmCost()
and TTI.getIntImmCostInst() for profitability
analysis. This patch implemented TTI.getIntImmCost()
properly for BPF backend which also prevented
transformation which caused the above test failures.

Differential Revision: https://reviews.llvm.org/D96448

(cherry picked from commit a260ae716030d5d2644a2af649501277d326bb21)


  Commit: f9efff398c1159b15964b166368b232f562e6cfc
      https://github.com/llvm/llvm-project/commit/f9efff398c1159b15964b166368b232f562e6cfc
  Author: Yonghong Song <yhs at fb.com>
  Date:   2021-05-03 (Mon, 03 May 2021)

  Changed paths:
    M llvm/lib/Target/BPF/CMakeLists.txt

  Log Message:
  -----------
  BPF: Add LLVMAnalysis in CMakefile LINK_COMPONENTS

buildbot reported a build error like below:
  BPFTargetMachine.cpp:(.text._ZN4llvm19TargetTransformInfo5ModelINS_10BPFTTIImplEED2Ev
    [_ZN4llvm19TargetTransformInfo5ModelINS_10BPFTTIImplEED2Ev]+0x14):
    undefined reference to `llvm::TargetTransformInfo::Concept::~Concept()'
  lib/Target/BPF/CMakeFiles/LLVMBPFCodeGen.dir/BPFTargetMachine.cpp.o:
    In function `llvm::TargetTransformInfo::Model<llvm::BPFTTIImpl>::~Model()':

Commit a260ae716030 ("BPF: Implement TTI.IntImmCost() properly")
added TargetTransformInfo to BPF, which requires LLVMAnalysis
dependence. In certain cmake configurations, lacking explicit
LLVMAnalysis dependency may cause compilation error.
Similar to other targets, this patch added LLVMAnalysis
in CMakefile LINK_COMPONENTS explicitly.

(cherry picked from commit 74975d35b47631da0c7911561f16d3ffd1af142a)


  Commit: 2460947eefc2176693a4aa4d05cd9733e38c7ffe
      https://github.com/llvm/llvm-project/commit/2460947eefc2176693a4aa4d05cd9733e38c7ffe
  Author: Yonghong Song <yhs at fb.com>
  Date:   2021-05-03 (Mon, 03 May 2021)

  Changed paths:
    M llvm/lib/Target/BPF/BPFTargetTransformInfo.h

  Log Message:
  -----------
  BPF: Implement TTI.getCmpSelInstrCost() properly

The Select insn in BPF is expensive as BPF backend
needs to resolve with conditionals.  This patch set
the getCmpSelInstrCost() to SCEVCheapExpansionBudget
for Select insn to prevent some Select insn related
optimizations.

This change is motivated during bcc code review for
   https://github.com/iovisor/bcc/pull/3270
where IndVarSimplifyPass eventually caused generating
the following asm code:
  ;       for (i = 0; (i < VIRTIO_MAX_SGS) && (i < num); i++) {
      14:       16 05 40 00 00 00 00 00 if w5 == 0 goto +64 <LBB0_6>
      15:       bc 51 00 00 00 00 00 00 w1 = w5
      16:       04 01 00 00 ff ff ff ff w1 += -1
      17:       67 05 00 00 20 00 00 00 r5 <<= 32
      18:       77 05 00 00 20 00 00 00 r5 >>= 32
      19:       a6 01 01 00 05 00 00 00 if w1 < 5 goto +1 <LBB0_4>
      20:       b7 05 00 00 06 00 00 00 r5 = 6
  00000000000000a8 <LBB0_4>:
      21:       b7 02 00 00 00 00 00 00 r2 = 0
      22:       b7 01 00 00 00 00 00 00 r1 = 0
  ;       for (i = 0; (i < VIRTIO_MAX_SGS) && (i < num); i++) {
      23:       7b 1a e0 ff 00 00 00 00 *(u64 *)(r10 - 32) = r1
      24:       7b 5a c0 ff 00 00 00 00 *(u64 *)(r10 - 64) = r5
Note that insn #15 has w1 = w5 and w1 is refined later but r5(w5) is
eventually saved on stack at insn #24 for later use. This cause
later verifier failures.

With this change, IndVarSimplifyPass won't do the above
transformation any more.

Differential Revision: https://reviews.llvm.org/D97479

(cherry picked from commit 1959ead525b8830cc8a345f45e1c3ef9902d3229)


  Commit: 6fe7c3728d1e98e05c67ceb03f429cb04a30e151
      https://github.com/llvm/llvm-project/commit/6fe7c3728d1e98e05c67ceb03f429cb04a30e151
  Author: Yonghong Song <yhs at fb.com>
  Date:   2021-05-03 (Mon, 03 May 2021)

  Changed paths:
    M llvm/lib/Target/BPF/CMakeLists.txt

  Log Message:
  -----------
  BPF: Add LLVMTransformUtils in CMakefile LINK_COMPONENTS

Commit 1959ead525b8 ("BPF: Implement TTI.getCmpSelInstrCost()
properly") introduced a dependency on LLVMTransformUtils
library. Let us encode this dependency explicitly in
CMakefile to avoid build error.

(cherry picked from commit 6d102f15a3af0a44cf2e26677e260bee425312f3)


Compare: https://github.com/llvm/llvm-project/compare/c27ad80507bf...6fe7c3728d1e