Skip to content

Prune unused constant expressions recursively. #678

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

Merged
maleadt merged 1 commit into from
Mar 24, 2025
Merged

Prune unused constant expressions recursively. #678

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
12 changes: 2 additions & 10 deletions src/irgen.jl
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -633,16 +633,8 @@ function add_kernel_state!(mod::LLVM.Module)

# ensure the old (stateless) functions don't have uses anymore, and remove them
for f in keys(workmap)
for use in uses(f)
val = user(use)
if val isa ConstantExpr
# XXX: shouldn't clone_into! remove unused CEs?
isempty(uses(val)) || error("old function still has uses (via a constant expr)")
LLVM.unsafe_destroy!(val)
else
error("old function still has uses")
end
end
prune_constexpr_uses!(f)
@assert isempty(uses(f))
replace_metadata_uses!(f, workmap[f])
erase!(f)
end
Expand Down
16 changes: 2 additions & 14 deletions src/metal.jl
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -406,14 +406,7 @@ function add_global_address_spaces!(@nospecialize(job::CompilerJob), mod::LLVM.M

# delete old globals
for (old, new) in global_map
for use in uses(old)
val = user(use)
if val isa ConstantExpr
# XXX: shouldn't clone_into! remove unused CEs?
isempty(uses(val)) || error("old function still has uses (via a constant expr)")
LLVM.unsafe_destroy!(val)
end
end
prune_constexpr_uses!(old)
@assert isempty(uses(old))
replace_metadata_uses!(old, new)
erase!(old)
Expand Down Expand Up @@ -637,12 +630,7 @@ function add_input_arguments!(@nospecialize(job::CompilerJob), mod::LLVM.Module,
# drop unused constants that may be referring to the old functions
# XXX: can we do this differently?
for f in worklist
for use in uses(f)
val = user(use)
if val isa LLVM.ConstantExpr && isempty(uses(val))
LLVM.unsafe_destroy!(val)
end
end
prune_constexpr_uses!(f)
end

# update other uses of the old function, modifying call sites to pass the arguments
Expand Down
17 changes: 17 additions & 0 deletions src/utils.jl
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -132,3 +132,20 @@ macro unlocked(ex)
end
esc(combinedef(def))
end


## constant expression pruning

# for some reason, after cloning the LLVM IR can contain unused constant expressions.
# these result in false positives when checking that values are unused and can be deleted.
# this helper function removes such unused constant expression uses of a value.
# the process needs to be recursive, as constant expressions can refer to one another.
function prune_constexpr_uses!(root::LLVM.Value)
for use in uses(root)
val = user(use)
if val isa ConstantExpr
prune_constexpr_uses!(val)
isempty(uses(val)) && LLVM.unsafe_destroy!(val)
end
end
end
Loading