diff options
| -rw-r--r-- | llvm/lib/Analysis/LazyValueInfo.cpp | 29 | ||||
| -rw-r--r-- | llvm/test/Transforms/CorrelatedValuePropagation/alloca.ll | 48 |
2 files changed, 77 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp index cf7c3f90abf..98831545f10 100644 --- a/llvm/lib/Analysis/LazyValueInfo.cpp +++ b/llvm/lib/Analysis/LazyValueInfo.cpp @@ -1601,8 +1601,26 @@ LazyValueInfo LazyValueAnalysis::run(Function &F, FunctionAnalysisManager &FAM) return LazyValueInfo(&AC, &TLI, DT); } +/// Returns true if we can statically tell that this value will never be a +/// "useful" constant. In practice, this means we've got something like an +/// alloca or a malloc call for which a comparison against a constant can +/// only be guarding dead code. Note that we are potentially giving up some +/// precision in dead code (a constant result) in favour of avoiding a +/// expensive search for a easily answered common query. +static bool isKnownNonConstant(Value *V) { + V = V->stripPointerCasts(); + // The return val of alloc cannot be a Constant. + if (isa<AllocaInst>(V)) + return true; + return false; +} + Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB, Instruction *CxtI) { + // Bail out early if V is known not to be a Constant. + if (isKnownNonConstant(V)) + return nullptr; + const DataLayout &DL = BB->getModule()->getDataLayout(); LVILatticeVal Result = getImpl(PImpl, AC, &DL, DT).getValueInBlock(V, BB, CxtI); @@ -1738,6 +1756,17 @@ LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C, LazyValueInfo::Tristate LazyValueInfo::getPredicateAt(unsigned Pred, Value *V, Constant *C, Instruction *CxtI) { + // Is or is not NonNull are common predicates being queried. If + // isKnownNonNull can tell us the result of the predicate, we can + // return it quickly. But this is only a fastpath, and falling + // through would still be correct. + if (V->getType()->isPointerTy() && C->isNullValue() && + isKnownNonNull(V->stripPointerCasts())) { + if (Pred == ICmpInst::ICMP_EQ) + return LazyValueInfo::False; + else if (Pred == ICmpInst::ICMP_NE) + return LazyValueInfo::True; + } const DataLayout &DL = CxtI->getModule()->getDataLayout(); LVILatticeVal Result = getImpl(PImpl, AC, &DL, DT).getValueAt(V, CxtI); Tristate Ret = getPredicateResult(Pred, C, Result, DL, TLI); diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/alloca.ll b/llvm/test/Transforms/CorrelatedValuePropagation/alloca.ll new file mode 100644 index 00000000000..2ae1664fdee --- /dev/null +++ b/llvm/test/Transforms/CorrelatedValuePropagation/alloca.ll @@ -0,0 +1,48 @@ +; RUN: opt -S -correlated-propagation -debug-only=lazy-value-info <%s 2>&1 | FileCheck %s +; +; Shortcut in Correlated Value Propagation ensures not to take Lazy Value Info +; analysis for %a.i and %tmp because %a.i is defined by alloca and %tmp is +; defined by alloca + bitcast. We know the ret value of alloca is nonnull. +; +; CHECK-NOT: LVI Getting edge value %a.i = alloca i64, align 8 at 'for.body' +; CHECK-NOT: LVI Getting edge value %tmp = bitcast i64* %a.i to i8* from 'for.cond' to 'for.body' +target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128" +target triple = "x86_64-unknown-linux-gnu" + +@.str = private unnamed_addr constant [8 x i8] c"a = %l\0A\00", align 1 + +; Function Attrs: argmemonly nounwind +declare void @llvm.lifetime.start(i64, i8* nocapture) + +declare void @hoo(i64*) + +declare i32 @printf(i8* nocapture readonly, ...) + +; Function Attrs: argmemonly nounwind +declare void @llvm.lifetime.end(i64, i8* nocapture) + +define void @goo(i32 %N, i64* %b) { +entry: + %a.i = alloca i64, align 8 + %tmp = bitcast i64* %a.i to i8* + %c = getelementptr inbounds i64, i64* %b, i64 0 + br label %for.cond + +for.cond: ; preds = %for.body, %entry + %i.0 = phi i32 [ 0, %entry ], [ %inc, %for.body ] + %cmp = icmp slt i32 %i.0, %N + br i1 %cmp, label %for.body, label %for.end + +for.body: ; preds = %for.cond + call void @llvm.lifetime.start(i64 8, i8* %tmp) + call void @hoo(i64* %a.i) + call void @hoo(i64* %c) + %tmp1 = load volatile i64, i64* %a.i, align 8 + %call.i = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str, i64 0, i64 0), i64 %tmp1) + call void @llvm.lifetime.end(i64 8, i8* %tmp) + %inc = add nsw i32 %i.0, 1 + br label %for.cond + +for.end: ; preds = %for.cond + ret void +} |
