Skip to content

[DFAJumpThreading] Try harder to avoid cycles in paths. #169151

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 3 commits into from
Nov 22, 2025
+223 −1
Merged

[DFAJumpThreading] Try harder to avoid cycles in paths. #169151

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
eddb26a
Precommit tests.
UsmanNadeem Nov 22, 2025
7194180
[DFAJumpThreading] Try harder to avoid cycles in paths.
UsmanNadeem Nov 22, 2025
333c742
Add transformation tests.
UsmanNadeem Nov 22, 2025
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: 10 additions & 1 deletion llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -625,8 +625,12 @@ struct AllSwitchPaths {
NewPath.setDeterminator(PhiBB);
NewPath.setExitValue(C);
// Don't add SwitchBlock at the start, this is handled later.
if (IncomingBB != SwitchBlock)
if (IncomingBB != SwitchBlock) {
// Don't add a cycle to the path.
if (VB.contains(IncomingBB))
continue;
NewPath.push_back(IncomingBB);
}
NewPath.push_back(PhiBB);
Res.push_back(NewPath);
continue;
Expand Down Expand Up @@ -815,7 +819,12 @@ struct AllSwitchPaths {

std::vector<ThreadingPath> TempList;
for (const ThreadingPath &Path : PathsToPhiDef) {
SmallPtrSet<BasicBlock *, 32> PathSet(Path.getPath().begin(),
Path.getPath().end());
for (const PathType &PathToSw : PathsToSwitchBB) {
if (any_of(llvm::drop_begin(PathToSw),
[&](const BasicBlock *BB) { return PathSet.contains(BB); }))
continue;
ThreadingPath PathCopy(Path);
PathCopy.appendExcludingFirst(PathToSw);
TempList.push_back(PathCopy);
Expand Down
77 changes: 77 additions & 0 deletions llvm/test/Transforms/DFAJumpThreading/dfa-jump-threading-analysis.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -246,5 +246,82 @@ exit:
ret i32 0
}

define i8 @cyclesInPaths1(i1 %call12, i1 %cmp18) {
; CHECK-LABEL: DFA Jump threading: cyclesInPaths1
; CHECK-NOT: <{{.*}}> [{{.*}}]

entry:
br label %switchPhiDef.for.body

switchPhiDef.for.body: ; preds = %detBB2, %entry
%switchPhi.curState = phi i32 [ %curState.1, %detBB2 ], [ 0, %entry ]
br i1 %call12, label %detBB1, label %if.else

if.else: ; preds = %switchPhiDef.for.body
br label %detBB1

detBB1: ; preds = %if.else, %switchPhiDef.for.body
%newState.02 = phi i32 [ 2, %switchPhiDef.for.body ], [ 4, %if.else ]
br i1 %cmp18, label %detBB2, label %if.end20

if.end20: ; preds = %detBB1
br i1 %call12, label %if.end23, label %switchBB

switchBB: ; preds = %if.end20
switch i32 %switchPhi.curState, label %if.end23 [
i32 4, label %ret1
i32 0, label %ret2
]

ret1: ; preds = %switchBB
ret i8 1

ret2: ; preds = %switchBB
ret i8 2

if.end23: ; preds = %switchBB, %if.end20
br label %detBB2

detBB2: ; preds = %if.end23, %detBB1
%curState.1 = phi i32 [ %newState.02, %if.end23 ], [ 0, %detBB1 ]
br label %switchPhiDef.for.body
}

define void @cyclesInPaths2(i1 %tobool5.not.i) {
; CHECK-LABEL: DFA Jump threading: cyclesInPaths2
; CHECK: < sw.bb.i, bb.exit, if.end5, if.end.i > [ 1, bb.exit ]
; CHECK-NEXT: < bb.exit, if.end5, if.end.i > [ 0, bb.exit ]

entry:
br label %if.end5

if.end5: ; preds = %bb.exit, %entry
%P.sroa.8.051 = phi i16 [ %retval.sroa.6.0.i, %bb.exit ], [ 0, %entry ]
call void @foo3()
br i1 %tobool5.not.i, label %if.end.i, label %bb.exit

if.end.i: ; preds = %if.end5
switch i16 %P.sroa.8.051, label %sw.default.i [
i16 1, label %sw.bb.i
i16 0, label %bb.exit
]

sw.bb.i: ; preds = %if.end.i
call void @foo1()
br label %bb.exit

sw.default.i: ; preds = %if.end.i
unreachable

bb.exit: ; preds = %sw.bb.i, %if.end.i, %if.end5
%retval.sroa.6.0.i = phi i16 [ 1, %sw.bb.i ], [ 0, %if.end5 ], [ 0, %if.end.i ]
call void @foo2()
br label %if.end5
}

declare void @foo1()
declare void @foo2()
declare void @foo3()

!0 = !{!"function_entry_count", i32 10}
!1 = !{!"branch_weights", i32 3, i32 5}
136 changes: 136 additions & 0 deletions llvm/test/Transforms/DFAJumpThreading/dfa-jump-threading-transform.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -499,6 +499,142 @@ cleanup: ; preds = %for.inc, %switchblock,
ret i16 0
}

define i8 @cyclesInPaths1(i1 %call12, i1 %cmp18) {
; CHECK-LABEL: @cyclesInPaths1(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[SWITCHPHIDEF_FOR_BODY:%.*]]
; CHECK: switchPhiDef.for.body:
; CHECK-NEXT: [[SWITCHPHI_CURSTATE:%.*]] = phi i32 [ [[CURSTATE_1:%.*]], [[DETBB2:%.*]] ], [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: br i1 [[CALL12:%.*]], label [[DETBB1:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.else:
; CHECK-NEXT: br label [[DETBB1]]
; CHECK: detBB1:
; CHECK-NEXT: [[NEWSTATE_02:%.*]] = phi i32 [ 2, [[SWITCHPHIDEF_FOR_BODY]] ], [ 4, [[IF_ELSE]] ]
; CHECK-NEXT: br i1 [[CMP18:%.*]], label [[DETBB2]], label [[IF_END20:%.*]]
; CHECK: if.end20:
; CHECK-NEXT: br i1 [[CALL12]], label [[IF_END23:%.*]], label [[SWITCHBB:%.*]]
; CHECK: switchBB:
; CHECK-NEXT: switch i32 [[SWITCHPHI_CURSTATE]], label [[IF_END23]] [
; CHECK-NEXT: i32 4, label [[RET1:%.*]]
; CHECK-NEXT: i32 0, label [[RET2:%.*]]
; CHECK-NEXT: ]
; CHECK: ret1:
; CHECK-NEXT: ret i8 1
; CHECK: ret2:
; CHECK-NEXT: ret i8 2
; CHECK: if.end23:
; CHECK-NEXT: br label [[DETBB2]]
; CHECK: detBB2:
; CHECK-NEXT: [[CURSTATE_1]] = phi i32 [ [[NEWSTATE_02]], [[IF_END23]] ], [ 0, [[DETBB1]] ]
; CHECK-NEXT: br label [[SWITCHPHIDEF_FOR_BODY]]
;
entry:
br label %switchPhiDef.for.body

switchPhiDef.for.body: ; preds = %detBB2, %entry
%switchPhi.curState = phi i32 [ %curState.1, %detBB2 ], [ 0, %entry ]
br i1 %call12, label %detBB1, label %if.else

if.else: ; preds = %switchPhiDef.for.body
br label %detBB1

detBB1: ; preds = %if.else, %switchPhiDef.for.body
%newState.02 = phi i32 [ 2, %switchPhiDef.for.body ], [ 4, %if.else ]
br i1 %cmp18, label %detBB2, label %if.end20

if.end20: ; preds = %detBB1
br i1 %call12, label %if.end23, label %switchBB

switchBB: ; preds = %if.end20
switch i32 %switchPhi.curState, label %if.end23 [
i32 4, label %ret1
i32 0, label %ret2
]

ret1: ; preds = %switchBB
ret i8 1

ret2: ; preds = %switchBB
ret i8 2

if.end23: ; preds = %switchBB, %if.end20
br label %detBB2

detBB2: ; preds = %if.end23, %detBB1
%curState.1 = phi i32 [ %newState.02, %if.end23 ], [ 0, %detBB1 ]
br label %switchPhiDef.for.body
}

define void @cyclesInPaths2(i1 %tobool) {
; CHECK-LABEL: @cyclesInPaths2(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[IF_END5:%.*]]
; CHECK: if.end5:
; CHECK-NEXT: [[P_SROA_8_051:%.*]] = phi i16 [ [[RETVAL_SROA_6_0_I:%.*]], [[BB_EXIT:%.*]] ], [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: call void (...) @llvm.fake.use(i32 3)
; CHECK-NEXT: br i1 [[TOBOOL:%.*]], label [[IF_END_I:%.*]], label [[BB_EXIT]]
; CHECK: if.end5.jt0:
; CHECK-NEXT: [[P_SROA_8_051_JT0:%.*]] = phi i16 [ [[RETVAL_SROA_6_0_I_JT0:%.*]], [[BB_EXIT_JT0:%.*]] ]
; CHECK-NEXT: call void (...) @llvm.fake.use(i32 3)
; CHECK-NEXT: br i1 [[TOBOOL]], label [[IF_END_I_JT0:%.*]], label [[BB_EXIT]]
; CHECK: if.end5.jt1:
; CHECK-NEXT: [[P_SROA_8_051_JT1:%.*]] = phi i16 [ [[RETVAL_SROA_6_0_I_JT1:%.*]], [[BB_EXIT_JT1:%.*]] ]
; CHECK-NEXT: call void (...) @llvm.fake.use(i32 3)
; CHECK-NEXT: br i1 [[TOBOOL]], label [[IF_END_I_JT1:%.*]], label [[BB_EXIT]]
; CHECK: if.end.i:
; CHECK-NEXT: switch i16 [[P_SROA_8_051]], label [[SW_DEFAULT_I:%.*]] [
; CHECK-NEXT: i16 1, label [[SW_BB_I:%.*]]
; CHECK-NEXT: i16 0, label [[BB_EXIT_JT0]]
; CHECK-NEXT: ]
; CHECK: if.end.i.jt0:
; CHECK-NEXT: br label [[BB_EXIT_JT0]]
; CHECK: if.end.i.jt1:
; CHECK-NEXT: br label [[SW_BB_I]]
; CHECK: sw.bb.i:
; CHECK-NEXT: call void (...) @llvm.fake.use(i32 1)
; CHECK-NEXT: br label [[BB_EXIT_JT1]]
; CHECK: sw.default.i:
; CHECK-NEXT: unreachable
; CHECK: bb.exit:
; CHECK-NEXT: [[RETVAL_SROA_6_0_I]] = phi i16 [ 0, [[IF_END5]] ], [ 0, [[IF_END5_JT1:%.*]] ], [ 0, [[IF_END5_JT0:%.*]] ]
; CHECK-NEXT: call void (...) @llvm.fake.use(i32 2)
; CHECK-NEXT: br label [[IF_END5]]
; CHECK: bb.exit.jt0:
; CHECK-NEXT: [[RETVAL_SROA_6_0_I_JT0]] = phi i16 [ 0, [[IF_END_I]] ], [ 0, [[IF_END_I_JT0]] ]
; CHECK-NEXT: call void (...) @llvm.fake.use(i32 2)
; CHECK-NEXT: br label [[IF_END5_JT0]]
; CHECK: bb.exit.jt1:
; CHECK-NEXT: [[RETVAL_SROA_6_0_I_JT1]] = phi i16 [ 1, [[SW_BB_I]] ]
; CHECK-NEXT: call void (...) @llvm.fake.use(i32 2)
; CHECK-NEXT: br label [[IF_END5_JT1]]
;
entry:
br label %if.end5

if.end5: ; preds = %bb.exit, %entry
%P.sroa.8.051 = phi i16 [ %retval.sroa.6.0.i, %bb.exit ], [ 0, %entry ]
call void (...) @llvm.fake.use(i32 3)
br i1 %tobool, label %if.end.i, label %bb.exit

if.end.i: ; preds = %if.end5
switch i16 %P.sroa.8.051, label %sw.default.i [
i16 1, label %sw.bb.i
i16 0, label %bb.exit
]

sw.bb.i: ; preds = %if.end.i
call void (...) @llvm.fake.use(i32 1)
br label %bb.exit

sw.default.i: ; preds = %if.end.i
unreachable

bb.exit: ; preds = %sw.bb.i, %if.end.i, %if.end5
%retval.sroa.6.0.i = phi i16 [ 1, %sw.bb.i ], [ 0, %if.end5 ], [ 0, %if.end.i ]
call void (...) @llvm.fake.use(i32 2)
br label %if.end5
}

declare void @llvm.fake.use(...)

!0 = !{!"function_entry_count", i32 10}
Expand Down