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Optimize specific function coalescing in lowering. (#5684)

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- Update all the llvm::Function pointers after function replacement.
Some were previously left in an inconsistent state.
- Only do function replacement once, after converging on the canonical
specific to use.
This commit is contained in:
Alina Sbirlea
2025-06-24 18:59:04 +00:00
committed by GitHub
parent badd544798
commit b0be6619ef
3 changed files with 69 additions and 48 deletions
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toolchain/lower/file_context.cpp
+55 -42
View File
@@ -188,12 +188,17 @@ auto FileContext::ContainsPair(
auto FileContext::CoalesceEquivalentSpecifics() -> void {
for (auto& specifics : lowered_specifics_.values()) {
// Collect specifics to delete for each generic. Replace and remove each
// after processing all specifics for a generic. Note, we could also
// replace and remove all specifics after processing all generics.
llvm::SmallVector<SemIR::SpecificId> specifics_to_delete;
// i cannot be unsigned due to the comparison with a negative number when
// the specifics vector is empty.
for (int i = 0; i < static_cast<int>(specifics.size()) - 1; ++i) {
// This specific was already replaced, skip it.
if (equivalent_specifics_.Get(specifics[i]).has_value() &&
equivalent_specifics_.Get(specifics[i]) != specifics[i]) {
specifics_to_delete.push_back(specifics[i]);
specifics[i] = specifics[specifics.size() - 1];
specifics.pop_back();
--i;
@@ -205,6 +210,7 @@ auto FileContext::CoalesceEquivalentSpecifics() -> void {
// When the specific was already replaced, skip it.
if (equivalent_specifics_.Get(specifics[j]).has_value() &&
equivalent_specifics_.Get(specifics[j]) != specifics[j]) {
specifics_to_delete.push_back(specifics[j]);
specifics[j] = specifics[specifics.size() - 1];
specifics.pop_back();
--j;
@@ -231,26 +237,18 @@ auto FileContext::CoalesceEquivalentSpecifics() -> void {
// When processing equivalences, we may change the canonical specific
// multiple times, so we don't delete replaced specifics until the
// end.
llvm::SmallVector<SemIR::SpecificId> specifics_to_delete;
visited_equivalent_specifics.ForEach(
[&](std::pair<SemIR::SpecificId, SemIR::SpecificId>
equivalent_entry) {
CARBON_VLOG("Found equivalent specifics: {0}, {1}",
equivalent_entry.first, equivalent_entry.second);
ProcessSpecificEquivalence(equivalent_entry,
specifics_to_delete);
ProcessSpecificEquivalence(equivalent_entry);
});
// Delete function bodies for already replaced functions.
for (auto specific_id : specifics_to_delete) {
specific_functions_.Get(specific_id)->eraseFromParent();
specific_functions_.Get(specific_id) =
specific_functions_.Get(equivalent_specifics_.Get(specific_id));
}
// Removed the replaced specific from the list of emitted specifics.
// Only the top level, since the others are somewhere else in the
// vector, they will be found and removed during processing.
specifics_to_delete.push_back(specifics[j]);
specifics[j] = specifics[specifics.size() - 1];
specifics.pop_back();
--j;
@@ -260,25 +258,27 @@ auto FileContext::CoalesceEquivalentSpecifics() -> void {
}
}
}
// Once all equivalences are found for a generic, update and delete up
// equivalent specifics.
for (auto specific_id : specifics_to_delete) {
UpdateAndDeleteLLVMFunction(specific_id);
}
}
}
auto FileContext::ProcessSpecificEquivalence(
std::pair<SemIR::SpecificId, SemIR::SpecificId> pair,
llvm::SmallVector<SemIR::SpecificId>& specifics_to_delete) -> void {
std::pair<SemIR::SpecificId, SemIR::SpecificId> pair) -> void {
auto [specific_id1, specific_id2] = pair;
CARBON_CHECK(specific_id1.has_value() && specific_id2.has_value(),
"Expected values in equivalence check");
auto get_canon = [&](SemIR::SpecificId specific_id) {
return equivalent_specifics_.Get(specific_id).has_value()
? std::make_pair(
equivalent_specifics_.Get(specific_id),
(equivalent_specifics_.Get(specific_id) != specific_id))
: std::make_pair(specific_id, false);
auto equiv_id = equivalent_specifics_.Get(specific_id);
return equiv_id.has_value() ? equiv_id : specific_id;
};
auto [canon_id1, replaced_before1] = get_canon(specific_id1);
auto [canon_id2, replaced_before2] = get_canon(specific_id2);
auto canon_id1 = get_canon(specific_id1);
auto canon_id2 = get_canon(specific_id2);
if (canon_id1 == canon_id2) {
// Already equivalent, there was a previous replacement.
@@ -288,7 +288,6 @@ auto FileContext::ProcessSpecificEquivalence(
if (canon_id1.index >= canon_id2.index) {
// Prefer the earlier index for canonical values.
std::swap(canon_id1, canon_id2);
std::swap(replaced_before1, replaced_before2);
}
// Update equivalent_specifics_ for all. This is used as an indicator that
@@ -296,11 +295,41 @@ auto FileContext::ProcessSpecificEquivalence(
// chains in `IsKnownEquivalence`.
equivalent_specifics_.Set(specific_id1, canon_id1);
equivalent_specifics_.Set(specific_id2, canon_id1);
specific_functions_.Get(canon_id2)->replaceAllUsesWith(
specific_functions_.Get(canon_id1));
if (!replaced_before2) {
specifics_to_delete.push_back(canon_id2);
equivalent_specifics_.Set(canon_id1, canon_id1);
equivalent_specifics_.Set(canon_id2, canon_id1);
}
auto FileContext::UpdateEquivalentSpecific(SemIR::SpecificId specific_id)
-> void {
if (!equivalent_specifics_.Get(specific_id).has_value()) {
return;
}
llvm::SmallVector<SemIR::SpecificId> stack;
SemIR::SpecificId specific_to_update = specific_id;
SemIR::SpecificId equivalent = equivalent_specifics_.Get(specific_to_update);
SemIR::SpecificId equivalent_next = equivalent_specifics_.Get(equivalent);
while (equivalent != equivalent_next) {
stack.push_back(specific_to_update);
specific_to_update = equivalent;
equivalent = equivalent_next;
equivalent_next = equivalent_specifics_.Get(equivalent_next);
}
for (auto specific : stack) {
equivalent_specifics_.Set(specific, equivalent);
}
}
auto FileContext::UpdateAndDeleteLLVMFunction(SemIR::SpecificId specific_id)
-> void {
UpdateEquivalentSpecific(specific_id);
auto* old_function = specific_functions_.Get(specific_id);
auto* new_function =
specific_functions_.Get(equivalent_specifics_.Get(specific_id));
old_function->replaceAllUsesWith(new_function);
old_function->eraseFromParent();
specific_functions_.Set(specific_id, new_function);
}
auto FileContext::IsKnownEquivalence(SemIR::SpecificId specific_id1,
@@ -310,24 +339,8 @@ auto FileContext::IsKnownEquivalence(SemIR::SpecificId specific_id1,
return false;
}
auto update_equivalent_specific = [&](SemIR::SpecificId specific_id) {
llvm::SmallVector<SemIR::SpecificId> stack;
SemIR::SpecificId specific_to_update = specific_id;
while (equivalent_specifics_.Get(
equivalent_specifics_.Get(specific_to_update)) !=
equivalent_specifics_.Get(specific_to_update)) {
stack.push_back(specific_to_update);
specific_to_update = equivalent_specifics_.Get(specific_to_update);
}
for (auto specific : llvm::reverse(stack)) {
equivalent_specifics_.Set(
specific,
equivalent_specifics_.Get(equivalent_specifics_.Get(specific)));
}
};
update_equivalent_specific(specific_id1);
update_equivalent_specific(specific_id2);
UpdateEquivalentSpecific(specific_id1);
UpdateEquivalentSpecific(specific_id2);
return equivalent_specifics_.Get(specific_id1) ==
equivalent_specifics_.Get(specific_id2);
toolchain/lower/file_context.h
+13 -5
View File
@@ -235,12 +235,9 @@ class FileContext {
visited_equivalent_specifics) -> bool;
// Given an equivalent pair of specifics, updates the canonical specific to
// use for each of the two Specifics found to be equivalent, replaces all
// uses of one specific with the canonical one, and adds the non-canonical
// specific to specifics_to_delete.
// use for each of the two Specifics found to be equivalent.
auto ProcessSpecificEquivalence(
std::pair<SemIR::SpecificId, SemIR::SpecificId> pair,
llvm::SmallVector<SemIR::SpecificId>& specifics_to_delete) -> void;
std::pair<SemIR::SpecificId, SemIR::SpecificId> pair) -> void;
// Checks if two specific_ids are equivalent and also reduces the equivalence
// chains/paths. This update ensures the canonical specific is always "one
@@ -248,6 +245,17 @@ class FileContext {
auto IsKnownEquivalence(SemIR::SpecificId specific_id1,
SemIR::SpecificId specific_id2) -> bool;
// Update the tracked equivalent specific for the `SpecificId`. This may
// occur a replacement was performed and a chain of such replacements needs
// to be followed to discover the canonical specific for the given argument.
auto UpdateEquivalentSpecific(SemIR::SpecificId specific_id) -> void;
// Update the LLVM function to use for a `SpecificId` that has been found to
// have another equivalent LLVM function. Replace all uses of the original
// LLVM function with the equivalent one found, and delete the previous LLVM
// function body.
auto UpdateAndDeleteLLVMFunction(SemIR::SpecificId specific_id) -> void;
// Inserts a pair into a set of pairs in canonical form. Also implicitly
// checks entry already existed if it cannot be inserted.
auto InsertPair(
toolchain/lower/testdata/function/generic/call_recursive_reorder_more.carbon
Vendored
+1 -1
View File
@@ -227,7 +227,7 @@ fn M() {
// CHECK:STDOUT:
// CHECK:STDOUT: ; uselistorder directives
// CHECK:STDOUT: uselistorder ptr @llvm.lifetime.start.p0, { 8, 7, 6, 5, 4, 3, 2, 1, 0 }
// CHECK:STDOUT: uselistorder ptr @_CF.Main.7776e910959584d9, { 5, 7, 6, 4, 3, 2, 1, 0 }
// CHECK:STDOUT: uselistorder ptr @_CF.Main.7776e910959584d9, { 5, 7, 6, 4, 0, 1, 2, 3 }
// CHECK:STDOUT:
// CHECK:STDOUT: attributes #0 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
// CHECK:STDOUT: