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libexpr: remove matchAttrs boolean from ExprLambda

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The boolean is only used to determine if the formals are set to a
non-null pointer in all our cases. We can get rid of that allocation and
instead just compare the pointer value with NULL. Saving up to
sizeof(bool) + platform specific alignment per ExprLambda instace.
Probably not a lot of memory but perhaps a few kilobyte with nixpkgs?

This also gets rid of a potential issue with dereferencing formals based on
the value of the boolean that didn't have to be aligned with the formals
pointer but was in all our cases.
This commit is contained in:
Andreas Rammhold 2021-10-06 17:08:08 +02:00
parent f45b30de2f
commit cae41eebff
8 changed files with 18 additions and 18 deletions
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4
src/libexpr/nixexpr.cc
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@ -124,7 +124,7 @@ void ExprList::show(std::ostream & str) const
void ExprLambda::show(std::ostream & str) const
{
str << "(";
if (matchAttrs) {
if (hasFormals()) {
str << "{ ";
bool first = true;
for (auto & i : formals->formals) {
@ -348,7 +348,7 @@ void ExprLambda::bindVars(const StaticEnv & env)
if (!arg.empty()) newEnv.vars[arg] = displ++;
if (matchAttrs) {
if (hasFormals()) {
for (auto & i : formals->formals)
newEnv.vars[i.name] = displ++;