[PATCH] D95543: [GVN] Clobber partially aliased loads.

[Jordan Rupprecht via Phabricator via llvm-commits]

rupprecht added a comment.

We're seeing some issues with this patch, potentially a miscompile. When we enable assertions we get an error about widening atomic loads -- I'm not sure this is the source of the miscompile we're seeing, but it certainly looks related (I think this is causing corruption and leading to issues elsewhere).

  $ cat repro.ll
  ; ModuleID = 'repro.ll'
  source_filename = "repro.ll"
  target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
  target triple = "x86_64-unknown-linux-gnu"
  
  %struct.widget = type { i32 }
  %struct.baz = type { i32, %struct.snork }
  %struct.snork = type { %struct.spam }
  %struct.spam = type { i32, i32 }
  
  @global = external local_unnamed_addr global %struct.widget, align 4
  @global.1 = external local_unnamed_addr global i8, align 1
  @global.2 = external local_unnamed_addr global i32, align 4
  
  define void @zot(%struct.baz* %arg) local_unnamed_addr align 2 {
  bb:
    %tmp = getelementptr inbounds %struct.baz, %struct.baz* %arg, i64 0, i32 1
    %tmp1 = bitcast %struct.snork* %tmp to i64*
    %tmp2 = load i64, i64* %tmp1, align 4
    %tmp3 = getelementptr inbounds %struct.baz, %struct.baz* %arg, i64 0, i32 1, i32 0, i32 1
    %tmp4 = icmp ugt i64 %tmp2, 4294967295
    br label %bb5
  
  bb5:                                              ; preds = %bb14, %bb
    %tmp6 = load i32, i32* %tmp3, align 4
    %tmp7 = icmp ne i32 %tmp6, 0
    %tmp8 = select i1 %tmp7, i1 %tmp4, i1 false
    %tmp9 = zext i1 %tmp8 to i8
    store i8 %tmp9, i8* @global.1, align 1
    %tmp10 = load i32, i32* @global.2, align 4
    switch i32 %tmp10, label %bb11 [
      i32 1, label %bb12
      i32 2, label %bb12
    ]
  
  bb11:                                             ; preds = %bb5
    br label %bb14
  
  bb12:                                             ; preds = %bb5, %bb5
    %tmp13 = load atomic i32, i32* getelementptr inbounds (%struct.widget, %struct.widget* @global, i64 0, i32 0) acquire, align 4
    br label %bb14
  
  bb14:                                             ; preds = %bb12, %bb11
    br label %bb5
  }
  $ opt -O2 repro.ll -disable-output
  opt: /home/rupprecht/src/llvm-project/llvm/lib/Transforms/Utils/VNCoercion.cpp:496: llvm::Value *llvm::VNCoercion::getLoadValueForLoad(llvm::LoadInst *, unsigned int, llvm::Type *, llvm::Instruction *, const llvm::DataLayout &): Assertion `SrcVal->isSimple() && "Cannot widen volatile/atomic load!"' failed.
  PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace.
  Stack dump:
  0.      Program arguments: /home/rupprecht/dev/opt -O2 repro.ll -disable-output
  ...
  #10 0x000000000768c138 llvm::VNCoercion::getLoadValueForLoad(llvm::LoadInst*, unsigned int, llvm::Type*, llvm::Instruction*, llvm::DataLayout const&) /home/rupprecht/src/llvm-project/llvm/lib/Transforms/Utils/VNCoercion.cpp:497:5
  #11 0x00000000070a01ad llvm::gvn::AvailableValue::MaterializeAdjustedValue(llvm::LoadInst*, llvm::Instruction*, llvm::GVN&) const /home/rupprecht/src/llvm-project/llvm/lib/Transforms/Scalar/GVN.cpp:902:11
  #12 0x00000000070ae067 llvm::gvn::AvailableValueInBlock::MaterializeAdjustedValue(llvm::LoadInst*, llvm::GVN&) const /home/rupprecht/src/llvm-project/llvm/lib/Transforms/Scalar/GVN.cpp:281:5
  #13 0x00000000070a1d11 ConstructSSAForLoadSet(llvm::LoadInst*, llvm::SmallVectorImpl<llvm::gvn::AvailableValueInBlock>&, llvm::GVN&) /home/rupprecht/src/llvm-project/llvm/lib/Transforms/Scalar/GVN.cpp:874:40
  #14 0x00000000070a3ce6 llvm::GVN::processNonLocalLoad(llvm::LoadInst*) /home/rupprecht/src/llvm-project/llvm/lib/Transforms/Scalar/GVN.cpp:1614:12
  #15 0x00000000070a610a llvm::GVN::processLoad(llvm::LoadInst*) /home/rupprecht/src/llvm-project/llvm/lib/Transforms/Scalar/GVN.cpp:1866:5
  #16 0x00000000070a7398 llvm::GVN::processInstruction(llvm::Instruction*) /home/rupprecht/src/llvm-project/llvm/lib/Transforms/Scalar/GVN.cpp:2292:9
  #17 0x00000000070a8175 llvm::GVN::processBlock(llvm::BasicBlock*) /home/rupprecht/src/llvm-project/llvm/lib/Transforms/Scalar/GVN.cpp:2490:24
  #18 0x00000000070a7c4f llvm::GVN::iterateOnFunction(llvm::Function&) /home/rupprecht/src/llvm-project/llvm/lib/Transforms/Scalar/GVN.cpp:2837:16
  #19 0x000000000709fdd6 llvm::GVN::runImpl(llvm::Function&, llvm::AssumptionCache&, llvm::DominatorTree&, llvm::TargetLibraryInfo const&, llvm::AAResults&, llvm::MemoryDependenceResults*, llvm::LoopInfo*, llvm::OptimizationRemarkEmitter*, llvm::MemorySSA*) /home/rupprecht/src/llvm-project/llvm/lib/Transforms/Scalar/GVN.cpp:2436:20
  #20 0x000000000709fa6e llvm::GVN::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) /home/rupprecht/src/llvm-project/llvm/lib/Transforms/Scalar/GVN.cpp:674:8
  #21 0x0000000007873fb7 llvm::detail::PassModel<llvm::Function, llvm::GVN, llvm::PreservedAnalyses, llvm::AnalysisManager<llvm::Function> >::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) /home/rupprecht/src/llvm-project/llvm/include/llvm/IR/PassManagerInternal.h:85:17
  #22 0x000000000691574c llvm::PassManager<llvm::Function, llvm::AnalysisManager<llvm::Function> >::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) /home/rupprecht/src/llvm-project/llvm/include/llvm/IR/PassManager.h:517:16
  #23 0x0000000004617e77 llvm::detail::PassModel<llvm::Function, llvm::PassManager<llvm::Function, llvm::AnalysisManager<llvm::Function> >, llvm::PreservedAnalyses, llvm::AnalysisManager<llvm::Function> >::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) /home/rupprecht/src/llvm-project/llvm/include/llvm/IR/PassManagerInternal.h:85:17


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