[Attributor] Remove restriction on simplifying function pointers

[nikic]

Summary

Dropping this restriction seems to work fine (there are no assertion failures), but I'm not sure whether this is guarding against some kind of silent CG corruption.

If doing this is still problematic, then the place to address it would probably be https://github.com/llvm/llvm-project/blob/8f5bdaf481c3f4e6876a5ae0e4d7c6ed2042e6a6/llvm/lib/Transforms/IPO/Attributor.cpp#L1856-L1859, which already prevents replacement outside the SCC, so I'm not quite sure what this check is intended to avoid.

[jdoerfert]

LG, assuming nothing breaks we probably restrict the problematic replacements already (or the updated got better).

llvm/lib/Transforms/IPO/AttributorAttributes.cpp

struct AAValueSimplifyArgument final : AAValueSimplifyImpl {
   void initialize(Attributor &A) override {
     AAValueSimplifyImpl::initialize(A);
     if (!getAnchorScope() || getAnchorScope()->isDeclaration())
       indicatePessimisticFixpoint();
     if (hasAttr({Attribute::InAlloca, Attribute::Preallocated,
                  Attribute::StructRet, Attribute::Nest, Attribute::ByVal},
                 /* IgnoreSubsumingPositions */ true))
       indicatePessimisticFixpoint();
-
-    // FIXME: This is a hack to prevent us from propagating function poiner in
-    // the new pass manager CGSCC pass as it creates call edges the
-    // CallGraphUpdater cannot handle yet.
-    Value &V = getAssociatedValue();
-    if (V.getType()->isPointerTy() &&
-        V.getType()->getPointerElementType()->isFunctionTy() &&
-        !A.isModulePass())
-      indicatePessimisticFixpoint();
   }
 
   /// See AbstractAttribute::updateImpl(...).
   ChangeStatus updateImpl(Attributor &A) override {
     // Byval is only replacable if it is readonly otherwise we would write into
     // the replaced value and not the copy that byval creates implicitly.
     Argument *Arg = getAssociatedArgument();
     if (Arg->hasByValAttr()) {

llvm/test/Transforms/Attributor/liveness.ll

 ; CHECK-LABEL: define {{[^@]+}}@call_via_pointer_with_dead_args
 ; CHECK-SAME: (i32* [[A:%.*]], i32* [[B:%.*]], void (i32*, i32*, i32*, i64, i32**)* nocapture nofree noundef nonnull [[FP:%.*]]) {
 ; CHECK-NEXT:    call void [[FP]](i32* [[A]], i32* [[B]], i32* [[A]], i64 -1, i32** null)
 ; CHECK-NEXT:    ret void
 ;
   call void %fp(i32* %a, i32* %b, i32* %a, i64 -1, i32** null)
   ret void
 }
-; FIXME: We have to prevent the propagation of %fp in the new pm CGSCC pass until the CallGraphUpdater can handle the new call edge.
+
 define internal void @call_via_pointer_with_dead_args_internal_a(i32* %a, i32* %b, void (i32*, i32*, i32*, i64, i32**)* %fp) {
 ; NOT_CGSCC_NPM-LABEL: define {{[^@]+}}@call_via_pointer_with_dead_args_internal_a
 ; NOT_CGSCC_NPM-SAME: (i32* [[A:%.*]], i32* noundef nonnull align 128 dereferenceable(4) [[B:%.*]]) {
 ; NOT_CGSCC_NPM-NEXT:    call void @called_via_pointer(i32* [[A]], i32* nonnull align 128 dereferenceable(4) [[B]], i32* [[A]], i64 -1, i32** null)
 ; NOT_CGSCC_NPM-NEXT:    ret void
 ;
 ; IS__CGSCC____-LABEL: define {{[^@]+}}@call_via_pointer_with_dead_args_internal_a
-; IS__CGSCC____-SAME: (i32* [[A:%.*]], i32* noundef nonnull align 128 dereferenceable(4) [[B:%.*]], void (i32*, i32*, i32*, i64, i32**)* nocapture nofree noundef nonnull [[FP:%.*]]) {
-; IS__CGSCC____-NEXT:    call void [[FP]](i32* [[A]], i32* nonnull align 128 dereferenceable(4) [[B]], i32* [[A]], i64 -1, i32** null)
+; IS__CGSCC____-SAME: (i32* [[A:%.*]], i32* noalias nocapture nofree nonnull readnone align 128 dereferenceable(4) [[B:%.*]]) {
+; IS__CGSCC____-NEXT:    call void @called_via_pointer(i32* [[A]], i32* noalias nocapture nofree nonnull readnone align 128 dereferenceable(4) undef, i32* noalias nocapture nofree readnone undef, i64 undef, i32** noalias nocapture nofree readnone align 4294967296 undef)
 ; IS__CGSCC____-NEXT:    ret void
 ;
   call void %fp(i32* %a, i32* %b, i32* %a, i64 -1, i32** null)
   ret void
 }
 define internal void @call_via_pointer_with_dead_args_internal_b(i32* %a, i32* %b, void (i32*, i32*, i32*, i64, i32**)* %fp) {
 ; NOT_CGSCC_NPM-LABEL: define {{[^@]+}}@call_via_pointer_with_dead_args_internal_b
 ; NOT_CGSCC_NPM-SAME: (i32* [[A:%.*]], i32* noundef nonnull align 128 dereferenceable(4) [[B:%.*]]) {
 ; NOT_CGSCC_NPM-NEXT:    call void @called_via_pointer_internal_2(i32* [[A]], i32* nonnull align 128 dereferenceable(4) [[B]], i32* [[A]], i64 -1, i32** null)
 ; NOT_CGSCC_NPM-NEXT:    ret void
 ;
 ; IS__CGSCC____-LABEL: define {{[^@]+}}@call_via_pointer_with_dead_args_internal_b
-; IS__CGSCC____-SAME: (i32* [[A:%.*]], i32* noundef nonnull align 128 dereferenceable(4) [[B:%.*]], void (i32*, i32*, i32*, i64, i32**)* nocapture nofree noundef nonnull [[FP:%.*]]) {
-; IS__CGSCC____-NEXT:    call void [[FP]](i32* [[A]], i32* nonnull align 128 dereferenceable(4) [[B]], i32* [[A]], i64 -1, i32** null)
+; IS__CGSCC____-SAME: (i32* [[A:%.*]], i32* noalias nocapture nofree nonnull readnone align 128 dereferenceable(4) [[B:%.*]]) {
+; IS__CGSCC____-NEXT:    call void @called_via_pointer_internal_2(i32* [[A]])
 ; IS__CGSCC____-NEXT:    ret void
 ;
   call void %fp(i32* %a, i32* %b, i32* %a, i64 -1, i32** null)
   ret void
 }
 define void @call_via_pointer_with_dead_args_caller(i32* %a, i32* %b) {
 ; NOT_CGSCC_NPM-LABEL: define {{[^@]+}}@call_via_pointer_with_dead_args_caller
 ; NOT_CGSCC_NPM-SAME: (i32* [[A:%.*]], i32* [[B:%.*]]) {
 ; NOT_CGSCC_NPM-NEXT:    [[PTR1:%.*]] = alloca i32, align 128
 ; NOT_CGSCC_NPM-NEXT:    [[PTR2:%.*]] = alloca i32, align 128
 ; NOT_CGSCC_NPM-NEXT:    [[PTR3:%.*]] = alloca i32, align 128
 ; NOT_CGSCC_NPM-NEXT:    [[PTR4:%.*]] = alloca i32, align 128
 ; NOT_CGSCC_NPM-NEXT:    call void @call_via_pointer_with_dead_args(i32* [[A]], i32* noundef nonnull align 128 dereferenceable(4) [[PTR1]], void (i32*, i32*, i32*, i64, i32**)* nocapture nofree noundef @called_via_pointer)
 ; NOT_CGSCC_NPM-NEXT:    call void @call_via_pointer_with_dead_args(i32* [[A]], i32* noundef nonnull align 128 dereferenceable(4) [[PTR2]], void (i32*, i32*, i32*, i64, i32**)* nocapture nofree noundef @called_via_pointer_internal_1)
 ; NOT_CGSCC_NPM-NEXT:    call void @call_via_pointer_with_dead_args_internal_a(i32* [[B]], i32* noundef nonnull align 128 dereferenceable(4) [[PTR3]])
 ; NOT_CGSCC_NPM-NEXT:    call void @call_via_pointer_with_dead_args_internal_b(i32* [[B]], i32* noundef nonnull align 128 dereferenceable(4) [[PTR4]])
 ; NOT_CGSCC_NPM-NEXT:    ret void
 ;
 ; IS__CGSCC____-LABEL: define {{[^@]+}}@call_via_pointer_with_dead_args_caller
 ; IS__CGSCC____-SAME: (i32* [[A:%.*]], i32* [[B:%.*]]) {
 ; IS__CGSCC____-NEXT:    [[PTR1:%.*]] = alloca i32, align 128
 ; IS__CGSCC____-NEXT:    [[PTR2:%.*]] = alloca i32, align 128
-; IS__CGSCC____-NEXT:    [[PTR3:%.*]] = alloca i32, align 128
-; IS__CGSCC____-NEXT:    [[PTR4:%.*]] = alloca i32, align 128
 ; IS__CGSCC____-NEXT:    call void @call_via_pointer_with_dead_args(i32* [[A]], i32* noundef nonnull align 128 dereferenceable(4) [[PTR1]], void (i32*, i32*, i32*, i64, i32**)* nocapture nofree noundef nonnull @called_via_pointer)
 ; IS__CGSCC____-NEXT:    call void @call_via_pointer_with_dead_args(i32* [[A]], i32* noundef nonnull align 128 dereferenceable(4) [[PTR2]], void (i32*, i32*, i32*, i64, i32**)* nocapture nofree noundef nonnull @called_via_pointer_internal_1)
-; IS__CGSCC____-NEXT:    call void @call_via_pointer_with_dead_args_internal_a(i32* [[B]], i32* noundef nonnull align 128 dereferenceable(4) [[PTR3]], void (i32*, i32*, i32*, i64, i32**)* nocapture nofree noundef nonnull @called_via_pointer)
-; IS__CGSCC____-NEXT:    call void @call_via_pointer_with_dead_args_internal_b(i32* [[B]], i32* noundef nonnull align 128 dereferenceable(4) [[PTR4]], void (i32*, i32*, i32*, i64, i32**)* nocapture nofree noundef nonnull @called_via_pointer_internal_2)
+; IS__CGSCC____-NEXT:    call void @call_via_pointer_with_dead_args_internal_a(i32* [[B]], i32* noalias nocapture nofree nonnull readnone align 128 dereferenceable(4) undef)
+; IS__CGSCC____-NEXT:    call void @call_via_pointer_with_dead_args_internal_b(i32* [[B]], i32* noalias nocapture nofree nonnull readnone align 128 dereferenceable(4) undef)
 ; IS__CGSCC____-NEXT:    ret void
 ;
   %ptr1 = alloca i32, align 128
   %ptr2 = alloca i32, align 128
   %ptr3 = alloca i32, align 128
   %ptr4 = alloca i32, align 128
   call void @call_via_pointer_with_dead_args(i32* %a, i32* %ptr1, void (i32*, i32*, i32*, i64, i32**)* @called_via_pointer)
   call void @call_via_pointer_with_dead_args(i32* %a, i32* %ptr2, void (i32*, i32*, i32*, i64, i32**)* @called_via_pointer_internal_1)

 ;
 entry:
   tail call void @use_i32p(i32* %a)
   tail call void @use_i32p(i32* %a)
   ret void
 }
 ; FIXME: Figure out why the MODULE has the unused arguments still
 define internal void @called_via_pointer_internal_2(i32* %a, i32* %b, i32* %c, i64 %d, i32** %e) {
-; CHECK-LABEL: define {{[^@]+}}@called_via_pointer_internal_2
-; CHECK-SAME: (i32* [[A:%.*]], i32* nocapture nofree readnone [[B:%.*]], i32* nocapture nofree readnone [[C:%.*]], i64 [[D:%.*]], i32** nocapture nofree readnone [[E:%.*]]) {
-; CHECK-NEXT:  entry:
-; CHECK-NEXT:    tail call void @use_i32p(i32* [[A]])
-; CHECK-NEXT:    tail call void @use_i32p(i32* [[A]])
-; CHECK-NEXT:    ret void
+; NOT_CGSCC_NPM-LABEL: define {{[^@]+}}@called_via_pointer_internal_2
+; NOT_CGSCC_NPM-SAME: (i32* [[A:%.*]], i32* nocapture nofree readnone [[B:%.*]], i32* nocapture nofree readnone [[C:%.*]], i64 [[D:%.*]], i32** nocapture nofree readnone [[E:%.*]]) {
+; NOT_CGSCC_NPM-NEXT:  entry:
+; NOT_CGSCC_NPM-NEXT:    tail call void @use_i32p(i32* [[A]])
+; NOT_CGSCC_NPM-NEXT:    tail call void @use_i32p(i32* [[A]])
+; NOT_CGSCC_NPM-NEXT:    ret void
+;
+; IS__CGSCC____-LABEL: define {{[^@]+}}@called_via_pointer_internal_2
+; IS__CGSCC____-SAME: (i32* [[A:%.*]]) {
+; IS__CGSCC____-NEXT:  entry:
+; IS__CGSCC____-NEXT:    tail call void @use_i32p(i32* [[A]])
+; IS__CGSCC____-NEXT:    tail call void @use_i32p(i32* [[A]])
+; IS__CGSCC____-NEXT:    ret void
 ;
 entry:
   tail call void @use_i32p(i32* %a)
   tail call void @use_i32p(i32* %a)
   ret void
 }
 declare void @use_i32p(i32*)
 

llvm/test/Transforms/Attributor/value-simplify.ll

 ; IS__TUNIT____-LABEL: define {{[^@]+}}@test_callee_is_undef
 ; IS__TUNIT____-SAME: (void (i32)* nocapture nofree [[FN:%.*]]) {
 ; IS__TUNIT____-NEXT:    call void @callee_is_undef()
 ; IS__TUNIT____-NEXT:    call void @unknown_calle_arg_is_undef(void (i32)* nocapture nofree [[FN]])
 ; IS__TUNIT____-NEXT:    ret void
 ;
 ; IS__CGSCC____-LABEL: define {{[^@]+}}@test_callee_is_undef
 ; IS__CGSCC____-SAME: (void (i32)* nocapture nofree [[FN:%.*]]) {
-; IS__CGSCC____-NEXT:    unreachable
+; IS__CGSCC____-NEXT:    call void @callee_is_undef()
+; IS__CGSCC____-NEXT:    call void @unknown_calle_arg_is_undef(void (i32)* nocapture nofree noundef nonnull [[FN]])
+; IS__CGSCC____-NEXT:    ret void
 ;
   call void @callee_is_undef(void ()* undef)
   call void @unknown_calle_arg_is_undef(void (i32)* %fn, i32 undef)
   ret void
 }
 define internal void @callee_is_undef(void ()* %fn) {
 ;
-; IS__TUNIT____-LABEL: define {{[^@]+}}@callee_is_undef() {
-; IS__TUNIT____-NEXT:    call void undef()
-; IS__TUNIT____-NEXT:    ret void
-;
-; IS__CGSCC____-LABEL: define {{[^@]+}}@callee_is_undef
-; IS__CGSCC____-SAME: (void ()* nocapture nofree noundef nonnull align 4294967296 [[FN:%.*]]) {
-; IS__CGSCC____-NEXT:    call void [[FN]]()
-; IS__CGSCC____-NEXT:    ret void
+; CHECK-LABEL: define {{[^@]+}}@callee_is_undef() {
+; CHECK-NEXT:    call void undef()
+; CHECK-NEXT:    ret void
 ;
   call void %fn()
   ret void
 }
 define internal void @unknown_calle_arg_is_undef(void (i32)* %fn, i32 %arg) {
 ;
 ; CHECK-LABEL: define {{[^@]+}}@unknown_calle_arg_is_undef
 ; CHECK-SAME: (void (i32)* nocapture nofree noundef nonnull [[FN:%.*]]) {