https://github.com/xlauko created
https://github.com/llvm/llvm-project/pull/232217
`getSuccessorRegions` must list every region that may run next. A
`cir.cleanup.scope` cleanup can also run from the middle of the body: on an
unwind out of a call, or on a `cir.return`, `cir.break`, `cir.continue` or
`cir.goto`. None of those is a region branch point, so a cleanup reached only
that way had no predecessor and generic MLIR passes treated it as dead. For
example, `cir-opt -remove-dead-values` erased this whole scope, store included:
```mlir
cir.cleanup.scope {
cir.call @may_throw() : () -> ()
cir.yield
} cleanup eh {
%c = cir.const #cir.int<7> : !s32i
cir.store %c, %p : !s32i, !cir.ptr<!s32i>
cir.yield
}
```
Now the cleanup region is a successor of the parent and of every body exit,
which stands in for those paths:
| Branch point | Before this patch | After this patch |
|---|---|---|
| entering the op | body | body or cleanup |
| body exit that the cleanup kind covers | cleanup | cleanup |
| body exit that the cleanup kind does not cover | leave the op | cleanup or
leave the op |
| cleanup exit | leave the op | leave the op |
A new lit test runs `-remove-dead-values` on the example above. Since every
region is now reachable, the unit test helper drops its `requireAllReachable`
flag.
Assisted-by: Claude Code (Claude Opus 5.5).
>From a4bd5965bf9d92ee00c50e8f7372689e5edf827f Mon Sep 17 00:00:00 2001
From: Henrich Lauko <[email protected]>
Date: Thu, 15 Oct 2026 07:46:35 +0000
Subject: [PATCH] [CIR] Keep cir.cleanup.scope cleanup regions reachable
RegionBranchOpInterface::getSuccessorRegions must return every region that
may run next, but an unwind out of a call in the body, or a cir.return,
cir.break, cir.continue or cir.goto out of it, runs the cleanup without
passing a region branch point. A cleanup reached only that way had no
predecessor, so generic passes treated it as dead, and -remove-dead-values
erased an EH cleanup that stores to memory. Now the cleanup region is a
successor of the parent and of every body exit, and a body exit that the
cleanup kind does not cover can also leave the op.
Co-Authored-By: Claude Opus 5.5 <[email protected]>
---
clang/lib/CIR/Dialect/IR/CIRDialect.cpp | 36 ++++++-------
.../remove-dead-values-cleanup-scope.cir | 33 ++++++++++++
clang/unittests/CIR/ControlFlowTest.cpp | 50 ++++++++++---------
3 files changed, 79 insertions(+), 40 deletions(-)
create mode 100644
clang/test/CIR/Transforms/remove-dead-values-cleanup-scope.cir
diff --git a/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
b/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
index f564eee053705..0e5e58a67768d 100644
--- a/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
+++ b/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
@@ -2045,31 +2045,33 @@ LogicalResult cir::CleanupScopeOp::verify() {
void cir::CleanupScopeOp::getSuccessorRegions(
mlir::RegionBranchPoint point, SmallVectorImpl<RegionSuccessor> ®ions) {
- // Execution always starts in the body region.
+ // The interface has no branch point for the paths that run the cleanup from
+ // the middle of the body: an unwind out of a call, or a cir.return,
+ // cir.break, cir.continue or cir.goto. The cleanup region is therefore a
+ // potential successor of every branch point in the body as well as of the
+ // parent. The edge from the parent stands in for such a path taken before
+ // the body has any effect, and the edges from body exits for one taken
+ // after some of its effects.
if (point.isParent()) {
regions.emplace_back(&getBodyRegion());
+ regions.emplace_back(&getCleanupRegion());
return;
}
mlir::Operation *term = point.getTerminatorPredecessorOrNull();
- assert(term && "expected a terminator predecessor");
-
- if (term->getParentRegion() == &getBodyRegion()) {
- // cir.resume unwinds out of the body. Every other terminator, such as
- // cir.yield or cir.co_return, is a normal exit.
- cir::CleanupKindAttr kind = getCleanupKindAttr();
- if (isa<cir::ResumeOp>(term) ? kind.isEH() : kind.isNormal()) {
- regions.emplace_back(&getCleanupRegion());
- return;
- }
+ if (term->getParentRegion() == &getCleanupRegion()) {
+ regions.emplace_back(getOperation());
+ return;
}
- // Exiting the cleanup region, or a body exit that skips it, leaves the
- // operation. An unwind out of the middle of the body is not a
- // RegionBranchPoint, and neither are cir.return, cir.break, cir.continue or
- // cir.goto, so a cleanup region reached only that way has no predecessor
- // here.
- regions.emplace_back(getOperation());
+ regions.emplace_back(&getCleanupRegion());
+
+ // cir.resume unwinds out of the body. Every other terminator, such as
+ // cir.yield or cir.co_return, is a normal exit. An exit that the cleanup
+ // kind does not cover can also leave the operation directly.
+ cir::CleanupKindAttr kind = getCleanupKindAttr();
+ if (isa<cir::ResumeOp>(term) ? !kind.isEH() : !kind.isNormal())
+ regions.emplace_back(getOperation());
}
LogicalResult cir::CleanupScopeOp::canonicalize(CleanupScopeOp op,
diff --git a/clang/test/CIR/Transforms/remove-dead-values-cleanup-scope.cir
b/clang/test/CIR/Transforms/remove-dead-values-cleanup-scope.cir
new file mode 100644
index 0000000000000..5aebe22a04739
--- /dev/null
+++ b/clang/test/CIR/Transforms/remove-dead-values-cleanup-scope.cir
@@ -0,0 +1,33 @@
+// RUN: cir-opt %s -remove-dead-values -o - | FileCheck %s
+
+// The EH cleanup runs only when @may_throw unwinds, which is not a region
+// branch point. The cleanup region must still count as reachable, or generic
+// passes such as -remove-dead-values erase it.
+
+!s32i = !cir.int<s, 32>
+
+module {
+ cir.func private @may_throw()
+
+ cir.func @eh_cleanup(%p : !cir.ptr<!s32i>) {
+ cir.cleanup.scope {
+ cir.call @may_throw() : () -> ()
+ cir.yield
+ } cleanup eh {
+ %c = cir.const #cir.int<7> : !s32i
+ cir.store %c, %p : !s32i, !cir.ptr<!s32i>
+ cir.yield
+ }
+ cir.return
+ }
+
+ // CHECK-LABEL: cir.func @eh_cleanup
+ // CHECK: cir.cleanup.scope {
+ // CHECK-NEXT: cir.call @may_throw() : () -> ()
+ // CHECK-NEXT: cir.yield
+ // CHECK-NEXT: } cleanup eh {
+ // CHECK-NEXT: %[[C:.*]] = cir.const #cir.int<7> : !s32i
+ // CHECK-NEXT: cir.store %[[C]], %{{.*}} : !s32i, !cir.ptr<!s32i>
+ // CHECK-NEXT: cir.yield
+ // CHECK-NEXT: }
+}
diff --git a/clang/unittests/CIR/ControlFlowTest.cpp
b/clang/unittests/CIR/ControlFlowTest.cpp
index e3a6d46ffdbbb..b12001c30cc90 100644
--- a/clang/unittests/CIR/ControlFlowTest.cpp
+++ b/clang/unittests/CIR/ControlFlowTest.cpp
@@ -80,13 +80,10 @@ static void expectTerminatorSuccessors(Region ®ion,
}
/// Verify control flow interface consistency beyond what mlir::verify checks:
-/// - Every non-empty region is reachable, unless `requireAllReachable` is
-/// false
+/// - Every non-empty region is reachable
/// - Every non-empty region has at least one branching terminator
/// - Op and terminator agree on successor regions at every branch point
-static void
-verifyControlFlowInterfaceConsistency(RegionBranchOpInterface op,
- bool requireAllReachable = true) {
+static void verifyControlFlowInterfaceConsistency(RegionBranchOpInterface op) {
EXPECT_TRUE(succeeded(mlir::verify(op)))
<< "MLIR verifier failed for '" << op->getName().getStringRef().str()
<< "'";
@@ -123,7 +120,7 @@
verifyControlFlowInterfaceConsistency(RegionBranchOpInterface op,
for (Region ®ion : op->getRegions()) {
if (region.empty())
continue;
- EXPECT_TRUE(!requireAllReachable || allReachable.contains(®ion))
+ EXPECT_TRUE(allReachable.contains(®ion))
<< "Region #" << region.getRegionNumber()
<< " is non-empty but not reachable from any branch point";
EXPECT_TRUE(regionsWithExit.contains(®ion))
@@ -135,18 +132,21 @@
verifyControlFlowInterfaceConsistency(RegionBranchOpInterface op,
}
/// Check a cir.cleanup.scope whose body has a single exit. The parent enters
-/// the body, the body exit enters the cleanup region if `bodyRunsCleanup` and
-/// leaves the op otherwise, and the cleanup region leaves the op.
+/// the body or the cleanup region. The body exit enters the cleanup region,
+/// and also leaves the op unless `bodyRunsCleanup`. The cleanup region leaves
+/// the op.
static void expectCleanupScopeSuccessors(cir::CleanupScopeOp op,
bool bodyRunsCleanup) {
Region &body = op.getBodyRegion();
Region &cleanup = op.getCleanupRegion();
- expectSuccessors(op, RegionBranchPoint::parent(), {&body});
+ expectSuccessors(op, RegionBranchPoint::parent(), {&body, &cleanup});
RegionBranchTerminatorOpInterface bodyTerm = getTerminator(body);
ASSERT_TRUE(bodyTerm);
- expectSuccessors(op, RegionBranchPoint(bodyTerm),
- {bodyRunsCleanup ? &cleanup : nullptr});
+ if (bodyRunsCleanup)
+ expectSuccessors(op, RegionBranchPoint(bodyTerm), {&cleanup});
+ else
+ expectSuccessors(op, RegionBranchPoint(bodyTerm), {&cleanup, nullptr});
expectTerminatorSuccessors(cleanup, {nullptr});
RegionBranchOpInterface branch = op;
@@ -154,10 +154,7 @@ static void
expectCleanupScopeSuccessors(cir::CleanupScopeOp op,
EXPECT_FALSE(branch.isRepetitiveRegion(1));
EXPECT_FALSE(branch.hasLoop());
- // Without the body edge nothing reaches the cleanup region.
- verifyControlFlowInterfaceConsistency(
- op,
- /*requireAllReachable=*/bodyRunsCleanup);
+ verifyControlFlowInterfaceConsistency(op);
}
//===----------------------------------------------------------------------===//
@@ -573,7 +570,8 @@ TEST_F(CIRControlFlowTest, CleanupScopeOpYieldEH) {
cir.return
}
)CIR");
- // An EH-only cleanup is skipped by the body's normal cir.yield.
+ // An EH-only cleanup does not run on the body's normal cir.yield, but stays
+ // a successor for an unwind from the middle of the body.
expectCleanupScopeSuccessors(findFirstOp<cir::CleanupScopeOp>(*module),
/*bodyRunsCleanup=*/false);
}
@@ -609,7 +607,8 @@ TEST_F(CIRControlFlowTest, CleanupScopeOpResumeNormal) {
cir.return
}
)CIR");
- // A normal-only cleanup is skipped by the body's unwinding cir.resume.
+ // A normal-only cleanup does not run on the body's unwinding cir.resume, but
+ // stays a successor for a cir.return or similar from the middle of the body.
expectCleanupScopeSuccessors(findFirstOp<cir::CleanupScopeOp>(*module),
/*bodyRunsCleanup=*/false);
}
@@ -637,8 +636,9 @@ TEST_F(CIRControlFlowTest,
CleanupScopeOpMultiBlockBodyNormal) {
)CIR");
auto cleanupScopeOp = findFirstOp<cir::CleanupScopeOp>(*module);
- expectSuccessors(cleanupScopeOp, RegionBranchPoint::parent(),
- {&cleanupScopeOp.getBodyRegion()});
+ expectSuccessors(
+ cleanupScopeOp, RegionBranchPoint::parent(),
+ {&cleanupScopeOp.getBodyRegion(), &cleanupScopeOp.getCleanupRegion()});
// The cir.brcond block is not a branch point, so only the two exiting
// blocks show up here.
@@ -653,15 +653,19 @@ TEST_F(CIRControlFlowTest,
CleanupScopeOpMultiBlockBodyNormal) {
EXPECT_TRUE(isa<cir::YieldOp>(*bodyTerms[0]));
EXPECT_TRUE(isa<cir::ResumeOp>(*bodyTerms[1]));
- // The normal exit runs the cleanup, the unwind exit skips it.
+ // The normal exit runs the cleanup. The unwind exit can also leave the op.
expectSuccessors(cleanupScopeOp, RegionBranchPoint(bodyTerms[0]),
{&cleanupScopeOp.getCleanupRegion()});
- expectSuccessors(cleanupScopeOp, RegionBranchPoint(bodyTerms[1]), {nullptr});
+ expectSuccessors(cleanupScopeOp, RegionBranchPoint(bodyTerms[1]),
+ {&cleanupScopeOp.getCleanupRegion(), nullptr});
expectTerminatorSuccessors(cleanupScopeOp.getCleanupRegion(), {nullptr});
- EXPECT_FALSE(asRegionBranch(cleanupScopeOp).hasLoop());
+ // hasLoop() reports a loop whenever two exits reach the same region, so
+ // check that no region can reach itself instead.
+ RegionBranchOpInterface branch = asRegionBranch(cleanupScopeOp);
+ EXPECT_FALSE(branch.isRepetitiveRegion(0));
+ EXPECT_FALSE(branch.isRepetitiveRegion(1));
- // The cleanup region does have a predecessor here, via the normal exit.
verifyControlFlowInterfaceConsistency(cleanupScopeOp);
}
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