diff options
| -rw-r--r-- | llvm/lib/Transforms/Scalar/SCCP.cpp | 64 | ||||
| -rw-r--r-- | llvm/test/Transforms/SCCP/switch-undef-constantfoldterminator.ll | 47 |
2 files changed, 86 insertions, 25 deletions
diff --git a/llvm/lib/Transforms/Scalar/SCCP.cpp b/llvm/lib/Transforms/Scalar/SCCP.cpp index adb70f3c257..d024e03b80a 100644 --- a/llvm/lib/Transforms/Scalar/SCCP.cpp +++ b/llvm/lib/Transforms/Scalar/SCCP.cpp @@ -1888,6 +1888,42 @@ static void findReturnsToZap(Function &F, } } +// Update the condition for terminators that are branching on indeterminate +// values, forcing them to use a specific edge. +static void forceIndeterminateEdge(Instruction* I, SCCPSolver &Solver) { + BasicBlock *Dest = nullptr; + Constant *C = nullptr; + if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) { + if (!isa<ConstantInt>(SI->getCondition())) { + // Indeterminate switch; use first case value. + Dest = SI->case_begin()->getCaseSuccessor(); + C = SI->case_begin()->getCaseValue(); + } + } else if (BranchInst *BI = dyn_cast<BranchInst>(I)) { + if (!isa<ConstantInt>(BI->getCondition())) { + // Indeterminate branch; use false. + Dest = BI->getSuccessor(1); + C = ConstantInt::getFalse(BI->getContext()); + } + } else if (IndirectBrInst *IBR = dyn_cast<IndirectBrInst>(I)) { + if (!isa<BlockAddress>(IBR->getAddress()->stripPointerCasts())) { + // Indeterminate indirectbr; use successor 0. + Dest = IBR->getSuccessor(0); + C = BlockAddress::get(IBR->getSuccessor(0)); + } + } else { + llvm_unreachable("Unexpected terminator instruction"); + } + if (C) { + assert(Solver.isEdgeFeasible(I->getParent(), Dest) && + "Didn't find feasible edge?"); + (void)Dest; + + I->setOperand(0, C); + } +} + + bool llvm::runIPSCCP( Module &M, const DataLayout &DL, const TargetLibraryInfo *TLI, function_ref<std::unique_ptr<PredicateInfo>(Function &)> getPredicateInfo) { @@ -2017,32 +2053,10 @@ bool llvm::runIPSCCP( // Ignore blockaddress users; BasicBlock's dtor will handle them. if (!I) continue; + // If we have forced an edge for an indeterminate value, then force the + // terminator to fold to that edge. + forceIndeterminateEdge(I, Solver); bool Folded = ConstantFoldTerminator(I->getParent()); - if (!Folded) { - // If the branch can't be folded, we must have forced an edge - // for an indeterminate value. Force the terminator to fold - // to that edge. - Constant *C; - BasicBlock *Dest; - if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) { - Dest = SI->case_begin()->getCaseSuccessor(); - C = SI->case_begin()->getCaseValue(); - } else if (BranchInst *BI = dyn_cast<BranchInst>(I)) { - Dest = BI->getSuccessor(1); - C = ConstantInt::getFalse(BI->getContext()); - } else if (IndirectBrInst *IBR = dyn_cast<IndirectBrInst>(I)) { - Dest = IBR->getSuccessor(0); - C = BlockAddress::get(IBR->getSuccessor(0)); - } else { - llvm_unreachable("Unexpected terminator instruction"); - } - assert(Solver.isEdgeFeasible(I->getParent(), Dest) && - "Didn't find feasible edge?"); - (void)Dest; - - I->setOperand(0, C); - Folded = ConstantFoldTerminator(I->getParent()); - } assert(Folded && "Expect TermInst on constantint or blockaddress to be folded"); (void) Folded; diff --git a/llvm/test/Transforms/SCCP/switch-undef-constantfoldterminator.ll b/llvm/test/Transforms/SCCP/switch-undef-constantfoldterminator.ll new file mode 100644 index 00000000000..169f0e83f1f --- /dev/null +++ b/llvm/test/Transforms/SCCP/switch-undef-constantfoldterminator.ll @@ -0,0 +1,47 @@ +; NOTE: Assertions have been autogenerated by utils/update_test_checks.py +; RUN: opt < %s -ipsccp -S | FileCheck %s + +; This test case used to end up like this: +; +; While deleting: label %lor.rhs +; Use still stuck around after Def is destroyed: br i1 undef, label %lor.rhs, label %land.end +; opt: ../lib/IR/Value.cpp: llvm::Value::~Value(): Assertion `use_empty() && "Uses remain when a value is destroyed!"' failed. +; +; due to ConstantFoldTerminator rewriting the switch into +; +; br i1 undef, label %lor.rhs, label %land.end +; +; while SCCP implementation relied on the terminator to always be folded into +; an unconditional branch when ConstantFoldTerminator returned true. + +define void @f4() { +; CHECK-LABEL: define void @f4( +; CHECK-NEXT: entry: +; CHECK-NEXT: [[CALL:%.*]] = call i16 @f3(i16 undef) +; CHECK-NEXT: ret void +; +entry: + %call = call i16 @f3(i16 undef) + ret void +} + +define internal i16 @f3(i16 %p1) { +; CHECK-LABEL: define internal i16 @f3( +; CHECK-NEXT: entry: +; CHECK-NEXT: br label [[LAND_END:%.*]] +; CHECK: land.end: +; CHECK-NEXT: ret i16 undef +; +entry: + switch i16 %p1, label %land.end [ + i16 0, label %land.end + i16 1, label %lor.rhs + ] + +lor.rhs: + br label %land.end + +land.end: + ret i16 0 +} + |
