diff --git a/llvm/lib/Analysis/TypeMetadataUtils.cpp b/llvm/lib/Analysis/TypeMetadataUtils.cpp index c55071a3685f49..65fa2bbcffd3c6 100644 --- a/llvm/lib/Analysis/TypeMetadataUtils.cpp +++ b/llvm/lib/Analysis/TypeMetadataUtils.cpp @@ -173,10 +173,19 @@ Constant *llvm::getPointerAtOffset(Constant *I, uint64_t Offset, Module &M, case Instruction::Sub: { auto *Operand0 = cast(C->getOperand(0)); auto *Operand1 = cast(C->getOperand(1)); - auto *Operand1TargetGlobal = getPointerAtOffset(Operand1, 0, M); + + auto StripGEP = [](Constant *C) { + auto *CE = dyn_cast(C); + if (!CE) + return C; + if (CE->getOpcode() != Instruction::GetElementPtr) + return C; + return CE->getOperand(0); + }; + auto *Operand1TargetGlobal = StripGEP(getPointerAtOffset(Operand1, 0, M)); // Check that in the "sub (@a, @b)" expression, @b points back to the top - // level global that we're processing. Otherwise bail. + // level global (or a GEP thereof) that we're processing. Otherwise bail. if (Operand1TargetGlobal != TopLevelGlobal) return nullptr; diff --git a/llvm/test/Transforms/GlobalDCE/virtual-functions-relative-pointers-gep.ll b/llvm/test/Transforms/GlobalDCE/virtual-functions-relative-pointers-gep.ll new file mode 100644 index 00000000000000..e49dc784af6124 --- /dev/null +++ b/llvm/test/Transforms/GlobalDCE/virtual-functions-relative-pointers-gep.ll @@ -0,0 +1,41 @@ +; RUN: opt < %s -passes='globaldce' -S | FileCheck %s + +target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128" + +declare { i8*, i1 } @llvm.type.checked.load(i8*, i32, metadata) + +; A vtable with "relative pointers", slots don't contain pointers to implementations, but instead have an i32 offset from the vtable itself to the implementation. +@vtable = internal unnamed_addr constant { [4 x i32] } { [4 x i32] [ + i32 42, + i32 1337, + i32 trunc (i64 sub (i64 ptrtoint (void ()* @vfunc1_live to i64), i64 ptrtoint (i32* getelementptr inbounds ({ [4 x i32] }, { [4 x i32] }* @vtable, i32 0, i32 0, i32 2) to i64)) to i32), + i32 trunc (i64 sub (i64 ptrtoint (void ()* @vfunc2_dead to i64), i64 ptrtoint (i32* getelementptr inbounds ({ [4 x i32] }, { [4 x i32] }* @vtable, i32 0, i32 0, i32 2) to i64)) to i32) +]}, align 8, !type !0, !type !1, !vcall_visibility !{i64 2} +!0 = !{i64 8, !"vfunc1.type"} +!1 = !{i64 12, !"vfunc2.type"} + +; CHECK: @vtable = internal unnamed_addr constant { [4 x i32] } { [4 x i32] [ +; CHECK-SAME: i32 trunc (i64 sub (i64 ptrtoint (void ()* @vfunc1_live to i64), i64 ptrtoint (i32* getelementptr inbounds ({ [4 x i32] }, { [4 x i32] }* @vtable, i32 0, i32 0, i32 2) to i64)) to i32), +; CHECK-SAME: i32 trunc (i64 sub (i64 0, i64 ptrtoint (i32* getelementptr inbounds ({ [4 x i32] }, { [4 x i32] }* @vtable, i32 0, i32 0, i32 2) to i64)) to i32) +; CHECK-SAME: ] }, align 8, !type !0, !type !1, !vcall_visibility !2 + +; (1) vfunc1_live is referenced from @main, stays alive +define internal void @vfunc1_live() { + ; CHECK: define internal void @vfunc1_live( + ret void +} + +; (2) vfunc2_dead is never referenced, gets removed and vtable slot is null'd +define internal void @vfunc2_dead() { + ; CHECK-NOT: define internal void @vfunc2_dead( + ret void +} + +define void @main() { + %1 = ptrtoint { [4 x i32] }* @vtable to i64 ; to keep @vtable alive + %2 = tail call { i8*, i1 } @llvm.type.checked.load(i8* null, i32 0, metadata !"vfunc1.type") + ret void +} + +!999 = !{i32 1, !"Virtual Function Elim", i32 1} +!llvm.module.flags = !{!999}