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Remove LLVM attribute removal
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This was necessary before, because `declare_raw_fn` would always apply
the default optimization attributes to every declared function,
and then `attributes::from_fn_attrs` would have to remove the default
attributes in the case of, e.g. `#[optimize(speed)]` in a `-Os` build.

However, every relevant callsite of `declare_raw_fn` (i.e. where we
actually generate code for the function, and not e.g. a call to an
intrinsic, where optimization attributes don't [?] matter)
calls `from_fn_attrs`, so we can simply remove the attribute setting
from `declare_raw_fn`, and rely on `from_fn_attrs` to apply the correct
attributes all at once.
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@erikdesjardins
erikdesjardins committed Feb 28, 2022
1 parent b07d59f commit dce14cf
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Showing 5 changed files with 13 additions and 87 deletions.
48 changes: 9 additions & 39 deletions compiler/rustc_codegen_llvm/src/attributes.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -28,12 +28,6 @@ pub fn apply_to_llfn(llfn: &Value, idx: AttributePlace, attrs: &[&Attribute]) {
}
}

pub fn remove_from_llfn(llfn: &Value, idx: AttributePlace, attrs: &[AttributeKind]) {
if !attrs.is_empty() {
llvm::RemoveFunctionAttributes(llfn, idx, attrs);
}
}

pub fn apply_to_callsite(callsite: &Value, idx: AttributePlace, attrs: &[&Attribute]) {
if !attrs.is_empty() {
llvm::AddCallSiteAttributes(callsite, idx, attrs);
Expand Down Expand Up @@ -217,38 +211,23 @@ pub fn non_lazy_bind_attr<'ll>(cx: &CodegenCx<'ll, '_>) -> Option<&'ll Attribute
}
}

/// Returns attributes to remove and to add, respectively,
/// to set the default optimizations attrs on a function.
/// Get the default optimizations attrs for a function.
#[inline]
pub(crate) fn default_optimisation_attrs<'ll>(
cx: &CodegenCx<'ll, '_>,
) -> (
// Attributes to remove
SmallVec<[AttributeKind; 3]>,
// Attributes to add
SmallVec<[&'ll Attribute; 2]>,
) {
let mut to_remove = SmallVec::new();
let mut to_add = SmallVec::new();
) -> SmallVec<[&'ll Attribute; 2]> {
let mut attrs = SmallVec::new();
match cx.sess().opts.optimize {
OptLevel::Size => {
to_remove.push(llvm::AttributeKind::MinSize);
to_add.push(llvm::AttributeKind::OptimizeForSize.create_attr(cx.llcx));
to_remove.push(llvm::AttributeKind::OptimizeNone);
attrs.push(llvm::AttributeKind::OptimizeForSize.create_attr(cx.llcx));
}
OptLevel::SizeMin => {
to_add.push(llvm::AttributeKind::MinSize.create_attr(cx.llcx));
to_add.push(llvm::AttributeKind::OptimizeForSize.create_attr(cx.llcx));
to_remove.push(llvm::AttributeKind::OptimizeNone);
}
OptLevel::No => {
to_remove.push(llvm::AttributeKind::MinSize);
to_remove.push(llvm::AttributeKind::OptimizeForSize);
to_remove.push(llvm::AttributeKind::OptimizeNone);
attrs.push(llvm::AttributeKind::MinSize.create_attr(cx.llcx));
attrs.push(llvm::AttributeKind::OptimizeForSize.create_attr(cx.llcx));
}
_ => {}
}
(to_remove, to_add)
attrs
}

/// Composite function which sets LLVM attributes for function depending on its AST (`#[attribute]`)
Expand All @@ -260,25 +239,17 @@ pub fn from_fn_attrs<'ll, 'tcx>(
) {
let codegen_fn_attrs = cx.tcx.codegen_fn_attrs(instance.def_id());

let mut to_remove = SmallVec::<[_; 4]>::new();
let mut to_add = SmallVec::<[_; 16]>::new();

match codegen_fn_attrs.optimize {
OptimizeAttr::None => {
let (to_remove_opt, to_add_opt) = default_optimisation_attrs(cx);
to_remove.extend(to_remove_opt);
to_add.extend(to_add_opt);
}
OptimizeAttr::Speed => {
to_remove.push(llvm::AttributeKind::MinSize);
to_remove.push(llvm::AttributeKind::OptimizeForSize);
to_remove.push(llvm::AttributeKind::OptimizeNone);
to_add.extend(default_optimisation_attrs(cx));
}
OptimizeAttr::Size => {
to_add.push(llvm::AttributeKind::MinSize.create_attr(cx.llcx));
to_add.push(llvm::AttributeKind::OptimizeForSize.create_attr(cx.llcx));
to_remove.push(llvm::AttributeKind::OptimizeNone);
}
OptimizeAttr::Speed => {}
}

let inline = if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
Expand Down Expand Up @@ -425,7 +396,6 @@ pub fn from_fn_attrs<'ll, 'tcx>(
to_add.push(llvm::CreateAttrStringValue(cx.llcx, cstr!("target-features"), &val));
}

attributes::remove_from_llfn(llfn, Function, &to_remove);
attributes::apply_to_llfn(llfn, Function, &to_add);
}

Expand Down
14 changes: 4 additions & 10 deletions compiler/rustc_codegen_llvm/src/declare.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -41,21 +41,15 @@ fn declare_raw_fn<'ll>(
llvm::SetFunctionCallConv(llfn, callconv);
llvm::SetUnnamedAddress(llfn, unnamed);

let mut attrs_to_remove = SmallVec::<[_; 4]>::new();
let mut attrs_to_add = SmallVec::<[_; 4]>::new();
let mut attrs = SmallVec::<[_; 4]>::new();

if cx.tcx.sess.opts.cg.no_redzone.unwrap_or(cx.tcx.sess.target.disable_redzone) {
attrs_to_add.push(llvm::AttributeKind::NoRedZone.create_attr(cx.llcx));
attrs.push(llvm::AttributeKind::NoRedZone.create_attr(cx.llcx));
}

let (to_remove, to_add) = attributes::default_optimisation_attrs(cx);
attrs_to_remove.extend(to_remove);
attrs_to_add.extend(to_add);
attrs.extend(attributes::non_lazy_bind_attr(cx));

attrs_to_add.extend(attributes::non_lazy_bind_attr(cx));

attributes::remove_from_llfn(llfn, Function, &attrs_to_remove);
attributes::apply_to_llfn(llfn, Function, &attrs_to_add);
attributes::apply_to_llfn(llfn, Function, &attrs);

llfn
}
Expand Down
6 changes: 0 additions & 6 deletions compiler/rustc_codegen_llvm/src/llvm/ffi.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1201,12 +1201,6 @@ extern "C" {
Attrs: *const &'a Attribute,
AttrsLen: size_t,
);
pub fn LLVMRustRemoveFunctionAttributes(
Fn: &Value,
index: c_uint,
Attrs: *const AttributeKind,
AttrsLen: size_t,
);

// Operations on parameters
pub fn LLVMIsAArgument(Val: &Value) -> Option<&Value>;
Expand Down
6 changes: 0 additions & 6 deletions compiler/rustc_codegen_llvm/src/llvm/mod.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -37,12 +37,6 @@ pub fn AddFunctionAttributes<'ll>(llfn: &'ll Value, idx: AttributePlace, attrs:
}
}

pub fn RemoveFunctionAttributes(llfn: &Value, idx: AttributePlace, attrs: &[AttributeKind]) {
unsafe {
LLVMRustRemoveFunctionAttributes(llfn, idx.as_uint(), attrs.as_ptr(), attrs.len());
}
}

pub fn AddCallSiteAttributes<'ll>(
callsite: &'ll Value,
idx: AttributePlace,
Expand Down
26 changes: 0 additions & 26 deletions compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -250,38 +250,12 @@ template<typename T> static inline void AddAttributes(T *t, unsigned Index,
t->setAttributes(PALNew);
}

template<typename T> static inline void RemoveAttributes(T *t, unsigned Index,
LLVMRustAttribute *RustAttrs,
size_t RustAttrsLen) {
AttributeList PAL = t->getAttributes();
AttributeList PALNew;
#if LLVM_VERSION_LT(14, 0)
AttrBuilder B;
for (LLVMRustAttribute RustAttr : makeArrayRef(RustAttrs, RustAttrsLen))
B.addAttribute(fromRust(RustAttr));
PALNew = PAL.removeAttributes(t->getContext(), Index, B);
#else
AttributeMask Mask;
for (LLVMRustAttribute RustAttr : makeArrayRef(RustAttrs, RustAttrsLen))
Mask.addAttribute(fromRust(RustAttr));
PALNew = PAL.removeAttributesAtIndex(t->getContext(), Index, Mask);
#endif
t->setAttributes(PALNew);
}

extern "C" void LLVMRustAddFunctionAttributes(LLVMValueRef Fn, unsigned Index,
LLVMAttributeRef *Attrs, size_t AttrsLen) {
Function *F = unwrap<Function>(Fn);
AddAttributes(F, Index, Attrs, AttrsLen);
}

extern "C" void LLVMRustRemoveFunctionAttributes(LLVMValueRef Fn, unsigned Index,
LLVMRustAttribute *RustAttrs,
size_t RustAttrsLen) {
Function *F = unwrap<Function>(Fn);
RemoveAttributes(F, Index, RustAttrs, RustAttrsLen);
}

extern "C" void LLVMRustAddCallSiteAttributes(LLVMValueRef Instr, unsigned Index,
LLVMAttributeRef *Attrs, size_t AttrsLen) {
CallBase *Call = unwrap<CallBase>(Instr);
Expand Down

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