0f46e31cfb
As part of the migration to ptradd (https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699), we need to change the representation of the `inrange` attribute, which is used for vtable splitting. Currently, inrange is specified as follows: ``` getelementptr inbounds ({ [4 x ptr], [4 x ptr] }, ptr @vt, i64 0, inrange i32 1, i64 2) ``` The `inrange` is placed on a GEP index, and all accesses must be "in range" of that index. The new representation is as follows: ``` getelementptr inbounds inrange(-16, 16) ({ [4 x ptr], [4 x ptr] }, ptr @vt, i64 0, i32 1, i64 2) ``` This specifies which offsets are "in range" of the GEP result. The new representation will continue working when canonicalizing to ptradd representation: ``` getelementptr inbounds inrange(-16, 16) (i8, ptr @vt, i64 48) ``` The inrange offsets are relative to the return value of the GEP. An alternative design could make them relative to the source pointer instead. The result-relative format was chosen on the off-chance that we want to extend support to non-constant GEPs in the future, in which case this variant is more expressive. This implementation "upgrades" the old inrange representation in bitcode by simply dropping it. This is a very niche feature, and I don't think trying to upgrade it is worthwhile. Let me know if you disagree.
46 lines
1.6 KiB
LLVM
46 lines
1.6 KiB
LLVM
; RUN: opt < %s -passes=globaldce -S | FileCheck %s
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; We currently only use llvm.type.checked.load for virtual function pointers,
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; not any other part of the vtable, so we can't remove the RTTI pointer even if
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; it's never going to be loaded from.
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target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
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%struct.A = type { ptr }
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; CHECK: @_ZTV1A = hidden unnamed_addr constant { [3 x ptr] } { [3 x ptr] [ptr null, ptr @_ZTI1A, ptr null] }, align 8, !type !0, !type !1, !vcall_visibility !2
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@_ZTV1A = hidden unnamed_addr constant { [3 x ptr] } { [3 x ptr] [ptr null, ptr @_ZTI1A, ptr @_ZN1A3fooEv] }, align 8, !type !0, !type !1, !vcall_visibility !2
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@_ZTS1A = hidden constant [3 x i8] c"1A\00", align 1
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@_ZTI1A = hidden constant { ptr, ptr } { ptr getelementptr inbounds (ptr, ptr @_ZTVN10__cxxabiv117__class_type_infoE, i64 2), ptr @_ZTS1A }, align 8
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define internal void @_ZN1AC2Ev(ptr %this) {
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entry:
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store ptr getelementptr inbounds inrange(-16, 8) ({ [3 x ptr] }, ptr @_ZTV1A, i64 0, i32 0, i64 2), ptr %this, align 8
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ret void
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}
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; CHECK-NOT: define {{.*}} @_ZN1A3fooEv(
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define internal void @_ZN1A3fooEv(ptr nocapture %this) {
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entry:
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ret void
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}
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define dso_local ptr @_Z6make_Av() {
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entry:
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%call = tail call ptr @_Znwm(i64 8)
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tail call void @_ZN1AC2Ev(ptr %call)
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ret ptr %call
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}
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declare dso_local noalias nonnull ptr @_Znwm(i64)
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@_ZTVN10__cxxabiv117__class_type_infoE = external dso_local global ptr
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!llvm.module.flags = !{!4}
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!0 = !{i64 16, !"_ZTS1A"}
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!1 = !{i64 16, !"_ZTSM1AFvvE.virtual"}
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!2 = !{i64 2} ; translation-unit vcall visibility
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!4 = !{i32 1, !"Virtual Function Elim", i32 1}
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