diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp --- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp +++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp @@ -1911,6 +1911,11 @@ }; Ptr = Ptr->stripPointerCasts(); + if (auto *I = dyn_cast(Ptr)) { + if (I->getParent() == &I->getFunction()->getEntryBlock()) { + return true; + } + } if (auto *GEP = dyn_cast(Ptr)) { return IsGuaranteedLoopInvariantBase(GEP->getPointerOperand()) && GEP->hasAllConstantIndices(); diff --git a/llvm/test/Transforms/DeadStoreElimination/MSSA/loop-invariant-entry-block.ll b/llvm/test/Transforms/DeadStoreElimination/MSSA/loop-invariant-entry-block.ll new file mode 100644 --- /dev/null +++ b/llvm/test/Transforms/DeadStoreElimination/MSSA/loop-invariant-entry-block.ll @@ -0,0 +1,49 @@ +; NOTE: Assertions have been autogenerated by utils/update_test_checks.py +; RUN: opt < %s -dse -S | FileCheck %s + +@BUFFER = external dso_local local_unnamed_addr global [0 x i8], align 1 + +define void @MissedDSEOpportunity(i64 %idx, i1* noalias %cc) { +; +; The DSE pass will try to kill the store in the loop exit block using the +; store in the function exit block. The loop invariant check on the pointer +; used by the stores should trivially return true because a pointer defined +; in the entry block of a function is loop invariant by definition. In fact +; the entry block of a function cannot have predecessors or be part of a loop. +; +; CHECK-LABEL: @MissedDSEOpportunity( +; CHECK-NEXT: entry: +; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds [0 x i8], [0 x i8]* @BUFFER, i64 0, i64 [[IDX:%.*]] +; CHECK-NEXT: [[BC:%.*]] = bitcast i8* [[GEP]] to i64* +; CHECK-NEXT: [[CC0:%.*]] = load volatile i1, i1* [[CC:%.*]], align 1 +; CHECK-NEXT: br i1 [[CC0]], label [[HEAD:%.*]], label [[EXIT:%.*]] +; CHECK: head: +; CHECK-NEXT: [[CC1:%.*]] = load volatile i1, i1* [[CC]], align 1 +; CHECK-NEXT: br i1 [[CC1]], label [[HEAD]], label [[EXIT_LOOPEXIT:%.*]] +; CHECK: exit.loopexit: +; CHECK-NEXT: br label [[EXIT]] +; CHECK: exit: +; CHECK-NEXT: store i64 0, i64* [[BC]], align 4 +; CHECK-NEXT: ret void +; +entry: + ; The entry block cannot have predecessors or be part of a loop + %gep = getelementptr inbounds [0 x i8], [0 x i8]* @BUFFER, i64 0, i64 %idx + %bc = bitcast i8* %gep to i64* + %cc0 = load volatile i1, i1* %cc, align 1 + br i1 %cc0, label %head, label %exit + +head: ; preds = %entry, %head + %cc1 = load volatile i1, i1* %cc, align 1 + br i1 %cc1, label %head, label %exit.loopexit + +exit.loopexit: ; preds = %head + ; Dead store + store i64 2, i64* %bc, align 4 + br label %exit + +exit: ; preds = %exit.loopexit, %entry + ; Killer store + store i64 0, i64* %bc, align 4 + ret void +} \ No newline at end of file