Skip to content

[FunctionAttrs] Infer errnomem location when accessing errno #129067

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 1 commit into
base: main
Choose a base branch
from
Open

[FunctionAttrs] Infer errnomem location when accessing errno #129067

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
11 changes: 11 additions & 0 deletions llvm/lib/Transforms/IPO/FunctionAttrs.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -136,6 +136,16 @@ static void addLocAccess(MemoryEffects &ME, const MemoryLocation &Loc,
ME |= MemoryEffects::argMemOnly(MR);
return;
}
if (auto *CI = dyn_cast<CallInst>(UO)) {
if (auto *Callee = CI->getCalledFunction(); Callee && Callee->hasName()) {
static constexpr auto ErrnoFnNames = {"__errno_location", "_errno",
"__errno", "___errno"};
Copy link
Contributor

@nikic nikic Oct 21, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This needs to go through TLI.

if (is_contained(ErrnoFnNames, Callee->getName())) {
ME |= MemoryEffects::errnoMemOnly(MR);
return;
}
}
}

// If it's not an identified object, it might be an argument.
if (!isIdentifiedObject(UO))
Expand Down Expand Up @@ -258,6 +268,7 @@ checkFunctionMemoryAccess(Function &F, bool ThisBody, AAResults &AAR,
if (I.isVolatile())
ME |= MemoryEffects::inaccessibleMemOnly(MR);

// Refine memory effects for the given location.
addLocAccess(ME, *Loc, MR, AAR);
}

Expand Down
56 changes: 56 additions & 0 deletions llvm/test/Transforms/FunctionAttrs/read-write-errno.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,56 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
; RUN: opt -passes=function-attrs -S < %s | FileCheck --check-prefixes=FNATTRS %s
; RUN: opt -passes=attributor-light -S < %s | FileCheck --check-prefixes=ATTRIBUTOR %s

define i32 @test_read_errno() {
; FNATTRS-LABEL: define i32 @test_read_errno() {
Copy link
Contributor

@nikic nikic Oct 21, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Looks like this isn't actually testing the inferred attributes. You need to pass --function-attrs or something like that to UTC.

; FNATTRS-NEXT: [[CALL:%.*]] = call ptr @__errno_location()
; FNATTRS-NEXT: [[ERRNO:%.*]] = load i32, ptr [[CALL]], align 4
; FNATTRS-NEXT: ret i32 [[ERRNO]]
;
; ATTRIBUTOR-LABEL: define i32 @test_read_errno() {
; ATTRIBUTOR-NEXT: [[CALL:%.*]] = call ptr @__errno_location()
; ATTRIBUTOR-NEXT: [[ERRNO:%.*]] = load i32, ptr [[CALL]], align 4
; ATTRIBUTOR-NEXT: ret i32 [[ERRNO]]
;
%call = call ptr @__errno_location()
%errno = load i32, ptr %call
ret i32 %errno
}

define ptr @test_write_errno() {
; FNATTRS-LABEL: define noundef ptr @test_write_errno() {
; FNATTRS-NEXT: [[CALL:%.*]] = call ptr @__errno_location()
; FNATTRS-NEXT: store i32 0, ptr [[CALL]], align 4
; FNATTRS-NEXT: ret ptr [[CALL]]
;
; ATTRIBUTOR-LABEL: define ptr @test_write_errno() {
; ATTRIBUTOR-NEXT: [[CALL:%.*]] = call ptr @__errno_location()
; ATTRIBUTOR-NEXT: store i32 0, ptr [[CALL]], align 4
; ATTRIBUTOR-NEXT: ret ptr [[CALL]]
;
%call = call ptr @__errno_location()
store i32 0, ptr %call
ret ptr %call
}

define i32 @test_readwrite_errno() {
; FNATTRS-LABEL: define i32 @test_readwrite_errno() {
; FNATTRS-NEXT: [[CALL:%.*]] = call ptr @__errno_location()
; FNATTRS-NEXT: store i32 0, ptr [[CALL]], align 4
; FNATTRS-NEXT: [[ERRNO:%.*]] = load i32, ptr [[CALL]], align 4
; FNATTRS-NEXT: ret i32 [[ERRNO]]
;
; ATTRIBUTOR-LABEL: define i32 @test_readwrite_errno() {
; ATTRIBUTOR-NEXT: [[CALL:%.*]] = call ptr @__errno_location()
; ATTRIBUTOR-NEXT: store i32 0, ptr [[CALL]], align 4
; ATTRIBUTOR-NEXT: [[ERRNO:%.*]] = load i32, ptr [[CALL]], align 4
; ATTRIBUTOR-NEXT: ret i32 [[ERRNO]]
;
%call = call ptr @__errno_location()
store i32 0, ptr %call
%errno = load i32, ptr %call
ret i32 %errno
}

declare ptr @__errno_location()