[llvm] r244879 - [LIR] Start leveraging the fundamental guarantees of a loop in

Thu Aug 13 04:12:07 PDT 2015

Hi Chandler,

I got this failure on my prototype bot:

http://buildmaster.tcwglab.linaro.org/builders/clang-cmake-aarch64-prototype/builds/87

clang-3.8: /home/rengolin/devel/buildslave/clang-cmake-aarch64-prototype/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp:836:
bool {anonymous}::LoopIdiomRecognize::recognizePopcount(): Assertion
`CurLoop->isLoopSimplifyForm() && "Loop passes require simplified
form!"' failed.
0  clang-3.8 0x00000000013613c4
llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 80
Stack dump:
0.      Program arguments:
/home/rengolin/devel/buildslave/clang-cmake-aarch64-prototype/stage1.install/bin/clang-3.8
-cc1 -triple aarch64-unknown-linux-gnu -emit-obj -disable-free
-main-file-name 2004-03-15-IndirectGoto.c -mrelocation-model static
-mthread-model posix -fmath-errno -masm-verbose -mconstructor-aliases
-fuse-init-array -target-cpu cortex-a57 -target-feature +neon
-target-feature +crc -target-feature +crypto -target-abi aapcs
-dwarf-column-info -coverage-file
/home/rengolin/devel/buildslave/clang-cmake-aarch64-prototype/test/sandbox/build/SingleSource/Regression/C/Output/2004-03-15-IndirectGoto.llvm.o
-resource-dir /home/rengolin/devel/buildslave/clang-cmake-aarch64-prototype/stage1.install/bin/../lib/clang/3.8.0
-I /home/rengolin/devel/buildslave/clang-cmake-aarch64-prototype/test/sandbox/build/SingleSource/Regression/C
-I /home/rengolin/devel/buildslave/clang-cmake-aarch64-prototype/test/test-suite/SingleSource/Regression/C
-I /home/rengolin/devel/buildslave/clang-cmake-aarch64-prototype/test/test-suite/include
-I ../../../include -D _GNU_SOURCE -D __STDC_LIMIT_MACROS -D NDEBUG
-internal-isystem /usr/local/include -internal-isystem
/home/rengolin/devel/buildslave/clang-cmake-aarch64-prototype/stage1.install/bin/../lib/clang/3.8.0/include
-internal-externc-isystem /usr/include/aarch64-linux-gnu
-internal-externc-isystem /include -internal-externc-isystem
/usr/include -O3 -fdebug-compilation-dir
/home/rengolin/devel/buildslave/clang-cmake-aarch64-prototype/test/sandbox/build/SingleSource/Regression/C
-ferror-limit 19 -fmessage-length 0 -mstackrealign
-fallow-half-arguments-and-returns -fno-signed-char -fobjc-runtime=gcc
-fdiagnostics-show-option -vectorize-loops -vectorize-slp -o
Output/2004-03-15-IndirectGoto.llvm.o -x c
/home/rengolin/devel/buildslave/clang-cmake-aarch64-prototype/test/test-suite/SingleSource/Regression/C/2004-03-15-IndirectGoto.c
1.      <eof> parser at end of file
2.      Per-module optimization passes
3.      Running pass 'CallGraph Pass Manager' on module
'/home/rengolin/devel/buildslave/clang-cmake-aarch64-prototype/test/test-suite/SingleSource/Regression/C/2004-03-15-IndirectGoto.c'.
4.      Running pass 'Loop Pass Manager' on function '@main'
5.      Running pass 'Recognize loop idioms' on basic block '%L3'
clang-3.8: error: unable to execute command: Aborted
clang-3.8: error: clang frontend command failed due to signal (use -v
to see invocation)

244880 still has the same problem...

cheers,
--renato

On 13 August 2015 at 10:56, Chandler Carruth via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: chandlerc
> Date: Thu Aug 13 04:56:20 2015
> New Revision: 244879
>
> URL: http://llvm.org/viewvc/llvm-project?rev=244879&view=rev
> Log:
> [LIR] Start leveraging the fundamental guarantees of a loop in
> simplified form to remove redundant checks and simplify the code for
> popcount recognition. We don't actually need to handle all of these
> cases.
>
> I've left a FIXME for one in particular until I finish inspecting to
> make sure we don't actually *rely* on the predicate in any way.
>
> Modified:
>     llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
>
> Modified: llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp?rev=244879&r1=244878&r2=244879&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp Thu Aug 13 04:56:20 2015
> @@ -830,29 +830,32 @@ bool LoopIdiomRecognize::recognizePopcou
>    // non-compact loop. Therefore, recognizing popcount idiom only makes sense
>    // in a compact loop.
>
> -  // Give up if the loop has multiple blocks or multiple backedges.
> -  if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
> +  assert(CurLoop->isLoopSimplifyForm() &&
> +         "Loop passes require simplified form!");
> +
> +  // Give up if the loop has multiple blocks.
> +  if (CurLoop->getNumBlocks() != 1)
>      return false;
>
> -  BasicBlock *LoopBody = *(CurLoop->block_begin());
> -  if (LoopBody->size() >= 20) {
> -    // The loop is too big, bail out.
> +  // If the loop is too big, bail out.
> +  BasicBlock &LoopBB = *CurLoop->getHeader();
> +  if (LoopBB.size() >= 20)
>      return false;
> -  }
>
>    // It should have a preheader containing nothing but an unconditional branch.
> -  BasicBlock *PH = CurLoop->getLoopPreheader();
> -  if (!PH)
> -    return false;
> -  if (&PH->front() != PH->getTerminator())
> +  BasicBlock &PH = *CurLoop->getLoopPreheader();
> +  if (&PH.front() != PH.getTerminator())
>      return false;
> -  auto *EntryBI = dyn_cast<BranchInst>(PH->getTerminator());
> +  // FIXME: Technically, it shouldn't matter what instruction we use as
> +  // a terminator, the only property needed is the definition of a preheader:
> +  // a single loop predecessor whose only successor is the loop header.
> +  auto *EntryBI = dyn_cast<BranchInst>(PH.getTerminator());
>    if (!EntryBI || EntryBI->isConditional())
>      return false;
>
>    // It should have a precondition block where the generated popcount instrinsic
>    // function can be inserted.
> -  auto *PreCondBB = PH->getSinglePredecessor();
> +  auto *PreCondBB = PH.getSinglePredecessor();
>    if (!PreCondBB)
>      return false;
>    auto *PreCondBI = dyn_cast<BranchInst>(PreCondBB->getTerminator());
>
>
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