Skip to content

[JTS] Use common branch weight downscaling #153738

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
merged 1 commit into from
Aug 15, 2025
Merged

[JTS] Use common branch weight downscaling #153738

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
14 changes: 6 additions & 8 deletions llvm/lib/Transforms/Scalar/JumpTableToSwitch.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -159,6 +159,10 @@ expandToSwitch(CallBase *CB, const JumpTableTy &JT, DomTreeUpdater &DTU,
DTUpdates.push_back({DominatorTree::Insert, B, Tail});

CallBase *Call = cast<CallBase>(CB->clone());
// The MD_prof metadata (VP kind), if it existed, can be dropped, it doesn't
// make sense on a direct call. Note that the values are used for the branch
// weights of the switch.
Call->setMetadata(LLVMContext::MD_prof, nullptr);
Call->setCalledFunction(Func);
Call->insertInto(B, B->end());
Switch->addCase(
Expand All @@ -180,14 +184,8 @@ expandToSwitch(CallBase *CB, const JumpTableTy &JT, DomTreeUpdater &DTU,
if (HadProfile && !ProfcheckDisableMetadataFixes) {
// At least one of the targets must've been taken.
assert(llvm::any_of(BranchWeights, [](uint64_t V) { return V != 0; }));
// FIXME: this duplicates logic in instrumentation. Note: since there's at
// least a nonzero and these are unsigned values, it follows MaxBW != 0.
uint64_t MaxBW = *llvm::max_element(BranchWeights);
SmallVector<uint32_t> ScaledBranchWeights(
llvm::map_range(BranchWeights, [MaxBW](uint64_t V) {
return static_cast<uint32_t>(V / MaxBW);
}));
setBranchWeights(*Switch, ScaledBranchWeights, /*IsExpected=*/false);
setBranchWeights(*Switch, downscaleWeights(BranchWeights),
/*IsExpected=*/false);
} else
setExplicitlyUnknownBranchWeights(*Switch);
if (PHI)
Expand Down
81 changes: 72 additions & 9 deletions llvm/test/Transforms/JumpTableToSwitch/basic.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,14 +1,39 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals all --version 4
; RUN: opt < %s -passes=jump-table-to-switch -verify-dom-info -S | FileCheck %s
; RUN: opt < %s -passes=jump-table-to-switch -jump-table-to-switch-size-threshold=0 -verify-dom-info -S | FileCheck %s --check-prefix=THRESHOLD-0

@func_array = constant [2 x ptr] [ptr @func0, ptr @func1]

;.
; CHECK: @func_array = constant [2 x ptr] [ptr @func0, ptr @func1]
; CHECK: @void_func_array = constant [2 x ptr] [ptr @void_func0, ptr @void_func1]
; CHECK: @func_array_addrspace_42 = addrspace(42) constant [2 x ptr addrspace(42)] [ptr addrspace(42) @func0_addrspace_42, ptr addrspace(42) @func1_addrspace_42]
;.
; THRESHOLD-0: @func_array = constant [2 x ptr] [ptr @func0, ptr @func1]
; THRESHOLD-0: @void_func_array = constant [2 x ptr] [ptr @void_func0, ptr @void_func1]
; THRESHOLD-0: @func_array_addrspace_42 = addrspace(42) constant [2 x ptr addrspace(42)] [ptr addrspace(42) @func0_addrspace_42, ptr addrspace(42) @func1_addrspace_42]
;.
define i32 @func0() !guid !0 {
; CHECK-LABEL: define i32 @func0(
; CHECK-SAME: ) !guid [[META0:![0-9]+]] {
; CHECK-NEXT: ret i32 1
;
; THRESHOLD-0-LABEL: define i32 @func0(
; THRESHOLD-0-SAME: ) !guid [[META0:![0-9]+]] {
; THRESHOLD-0-NEXT: ret i32 1
;
ret i32 1
}

define i32 @func1() !guid !1 {
; CHECK-LABEL: define i32 @func1(
; CHECK-SAME: ) !guid [[META1:![0-9]+]] {
; CHECK-NEXT: ret i32 2
;
; THRESHOLD-0-LABEL: define i32 @func1(
; THRESHOLD-0-SAME: ) !guid [[META1:![0-9]+]] {
; THRESHOLD-0-NEXT: ret i32 2
;
ret i32 2
}

Expand All @@ -20,7 +45,7 @@ define i32 @function_with_jump_table(i32 %index) {
; CHECK-NEXT: switch i32 [[INDEX]], label [[DEFAULT_SWITCH_CASE_UNREACHABLE:%.*]] [
; CHECK-NEXT: i32 0, label [[CALL_0:%.*]]
; CHECK-NEXT: i32 1, label [[CALL_1:%.*]]
; CHECK-NEXT: ]
; CHECK-NEXT: ], !prof [[PROF2:![0-9]+]]
; CHECK: default.switch.case.unreachable:
; CHECK-NEXT: unreachable
; CHECK: call.0:
Expand All @@ -37,7 +62,7 @@ define i32 @function_with_jump_table(i32 %index) {
; THRESHOLD-0-SAME: i32 [[INDEX:%.*]]) {
; THRESHOLD-0-NEXT: [[GEP:%.*]] = getelementptr inbounds [2 x ptr], ptr @func_array, i32 0, i32 [[INDEX]]
; THRESHOLD-0-NEXT: [[FUNC_PTR:%.*]] = load ptr, ptr [[GEP]], align 8
; THRESHOLD-0-NEXT: [[RESULT:%.*]] = call i32 [[FUNC_PTR]]()
; THRESHOLD-0-NEXT: [[RESULT:%.*]] = call i32 [[FUNC_PTR]](), !prof [[PROF2:![0-9]+]]
; THRESHOLD-0-NEXT: ret i32 [[RESULT]]
;
%gep = getelementptr inbounds [2 x ptr], ptr @func_array, i32 0, i32 %index
Expand All @@ -54,7 +79,7 @@ define i32 @basic_block_splitted_twice(i32 %index) {
; CHECK-NEXT: switch i32 [[INDEX]], label [[DEFAULT_SWITCH_CASE_UNREACHABLE:%.*]] [
; CHECK-NEXT: i32 0, label [[CALL_0:%.*]]
; CHECK-NEXT: i32 1, label [[CALL_1:%.*]]
; CHECK-NEXT: ]
; CHECK-NEXT: ], !prof [[PROF3:![0-9]+]]
; CHECK: default.switch.case.unreachable:
; CHECK-NEXT: unreachable
; CHECK: call.0:
Expand All @@ -70,7 +95,7 @@ define i32 @basic_block_splitted_twice(i32 %index) {
; CHECK-NEXT: switch i32 [[INDEX]], label [[DEFAULT_SWITCH_CASE_UNREACHABLE1:%.*]] [
; CHECK-NEXT: i32 0, label [[CALL_02:%.*]]
; CHECK-NEXT: i32 1, label [[CALL_13:%.*]]
; CHECK-NEXT: ]
; CHECK-NEXT: ], !prof [[PROF3]]
; CHECK: default.switch.case.unreachable1:
; CHECK-NEXT: unreachable
; CHECK: call.02:
Expand Down Expand Up @@ -106,10 +131,22 @@ define i32 @basic_block_splitted_twice(i32 %index) {
}

define void @void_func0() {
; CHECK-LABEL: define void @void_func0() {
; CHECK-NEXT: ret void
;
; THRESHOLD-0-LABEL: define void @void_func0() {
; THRESHOLD-0-NEXT: ret void
;
ret void
}

define void @void_func1() {
; CHECK-LABEL: define void @void_func1() {
; CHECK-NEXT: ret void
;
; THRESHOLD-0-LABEL: define void @void_func1() {
; THRESHOLD-0-NEXT: ret void
;
ret void
}

Expand All @@ -123,7 +160,7 @@ define void @void_function_with_jump_table(i32 %index) {
; CHECK-NEXT: switch i32 [[INDEX]], label [[DEFAULT_SWITCH_CASE_UNREACHABLE:%.*]] [
; CHECK-NEXT: i32 0, label [[CALL_0:%.*]]
; CHECK-NEXT: i32 1, label [[CALL_1:%.*]]
; CHECK-NEXT: ]
; CHECK-NEXT: ], !prof [[PROF3]]
; CHECK: default.switch.case.unreachable:
; CHECK-NEXT: unreachable
; CHECK: call.0:
Expand Down Expand Up @@ -156,7 +193,7 @@ define void @void_function_with_jump_table_and_call_site_attr(i32 %index) {
; CHECK-NEXT: switch i32 [[INDEX]], label [[DEFAULT_SWITCH_CASE_UNREACHABLE:%.*]] [
; CHECK-NEXT: i32 0, label [[CALL_0:%.*]]
; CHECK-NEXT: i32 1, label [[CALL_1:%.*]]
; CHECK-NEXT: ]
; CHECK-NEXT: ], !prof [[PROF3]]
; CHECK: default.switch.case.unreachable:
; CHECK-NEXT: unreachable
; CHECK: call.0:
Expand All @@ -183,10 +220,22 @@ define void @void_function_with_jump_table_and_call_site_attr(i32 %index) {


define i32 @func0_addrspace_42() addrspace(42) {
; CHECK-LABEL: define i32 @func0_addrspace_42() addrspace(42) {
; CHECK-NEXT: ret i32 1
;
; THRESHOLD-0-LABEL: define i32 @func0_addrspace_42() addrspace(42) {
; THRESHOLD-0-NEXT: ret i32 1
;
ret i32 1
}

define i32 @func1_addrspace_42() addrspace(42) {
; CHECK-LABEL: define i32 @func1_addrspace_42() addrspace(42) {
; CHECK-NEXT: ret i32 2
;
; THRESHOLD-0-LABEL: define i32 @func1_addrspace_42() addrspace(42) {
; THRESHOLD-0-NEXT: ret i32 2
;
ret i32 2
}

Expand All @@ -200,7 +249,7 @@ define i32 @function_with_jump_table_addrspace_42(i32 %index) addrspace(42) {
; CHECK-NEXT: switch i32 [[INDEX]], label [[DEFAULT_SWITCH_CASE_UNREACHABLE:%.*]] [
; CHECK-NEXT: i32 0, label [[CALL_0:%.*]]
; CHECK-NEXT: i32 1, label [[CALL_1:%.*]]
; CHECK-NEXT: ]
; CHECK-NEXT: ], !prof [[PROF3]]
; CHECK: default.switch.case.unreachable:
; CHECK-NEXT: unreachable
; CHECK: call.0:
Expand Down Expand Up @@ -228,4 +277,18 @@ define i32 @function_with_jump_table_addrspace_42(i32 %index) addrspace(42) {

!0 = !{i64 5678}
!1 = !{i64 5555}
!2 = !{!"VP", i32 0, i64 25, i64 5678, i64 20, i64 5555, i64 5}
!2 = !{!"VP", i32 0, i64 25, i64 5678, i64 20, i64 5555, i64 5}
;.
; CHECK: attributes #[[ATTR0]] = { nounwind }
;.
; THRESHOLD-0: attributes #[[ATTR0]] = { nounwind }
;.
; CHECK: [[META0]] = !{i64 5678}
; CHECK: [[META1]] = !{i64 5555}
; CHECK: [[PROF2]] = !{!"branch_weights", i32 0, i32 20, i32 5}
; CHECK: [[PROF3]] = !{!"unknown"}
;.
; THRESHOLD-0: [[META0]] = !{i64 5678}
; THRESHOLD-0: [[META1]] = !{i64 5555}
; THRESHOLD-0: [[PROF2]] = !{!"VP", i32 0, i64 25, i64 5678, i64 20, i64 5555, i64 5}
;.