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[CIR] Handle the 'before case' block of a switch statement. #199752

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Merged
erichkeane merged 2 commits into from
May 27, 2026
Merged

[CIR] Handle the 'before case' block of a switch statement. #199752

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[CIR] Handle the 'before case' block of a switch statement.
erichkeane May 21, 2026
6ce930f
Clang-format
erichkeane May 26, 2026
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33 changes: 29 additions & 4 deletions clang/lib/CIR/CodeGen/CIRGenStmt.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -803,7 +803,7 @@ CIRGenFunction::emitCaseDefaultCascade(const T *stmt, mlir::Type condType,
// If the substmt is default stmt or case stmt, try to handle the special case
// to make it into the simple form. e.g.
//
// swtich () {
// switch () {
// case 1:
// default:
// ...
Expand Down Expand Up @@ -1165,10 +1165,35 @@ mlir::LogicalResult CIRGenFunction::emitSwitchBody(const Stmt *s) {

auto *compoundStmt = cast<CompoundStmt>(s);

mlir::Block *swtichBlock = builder.getBlock();
for (auto *c : compoundStmt->body()) {
ArrayRef<Stmt *> body{compoundStmt->body_begin(), compoundStmt->body_end()};
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@andykaylor andykaylor May 27, 2026

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Can you not use compoundStmt->body() here?

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@erichkeane erichkeane May 27, 2026

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No, thats an iterator_range. I could use that instead of array-ref for the range, but it doesn't have a 'drop-front' type function.


mlir::Block *switchBlock = builder.getBlock();

// Any statements appearing before the first case statement are 'unassociated'
// with anything. So we have to create them FIRST in their own block. After
// that, the 'case' regions will take care of future ones.
if (!body.empty() && !isa<SwitchCase>(body.front())) {
builder.setInsertionPointToEnd(switchBlock);
while (!body.empty() && !isa<SwitchCase>(body.front())) {

auto *c = body.front();
if (mlir::failed(emitStmt(c, /*useCurrentScope=*/!isa<CompoundStmt>(c))))
return mlir::failure();

body = body.drop_front();
}

// Now that we've emitted ALL of the statements, we can create a new block
// for the actual case statements/etc to appear.
mlir::Block *lastBlock = builder.getBlock();
switchBlock = builder.createBlock(switchBlock->getParent());
builder.setInsertionPointToEnd(lastBlock);
cir::BrOp::create(builder, getLoc(s->getSourceRange()), switchBlock);
}

for (auto *c : body) {
if (auto *switchCase = dyn_cast<SwitchCase>(c)) {
builder.setInsertionPointToEnd(swtichBlock);
builder.setInsertionPointToEnd(switchBlock);
// Reset insert point automatically, so that we can attach following
// random stmt to the region of previous built case op to try to make
// the being generated `cir.switch` to be in simple form.
Expand Down
31 changes: 17 additions & 14 deletions clang/lib/CIR/Dialect/Transforms/FlattenCFG.cpp
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Expand Up @@ -301,15 +301,16 @@ class CIRSwitchOpFlattening : public mlir::OpRewritePattern<cir::SwitchOp> {
if (hasNestedOpsToFlatten(region))
return mlir::failure();

llvm::SmallVector<CaseOp> cases;
op.collectCases(cases);

// Empty switch statement: just erase it.
if (cases.empty()) {
if (op.getBody().hasOneBlock() &&
op.getBody().front().without_terminator().empty()) {
rewriter.eraseOp(op);
return mlir::success();
}

llvm::SmallVector<CaseOp> cases;
op.collectCases(cases);

// Create exit block from the next node of cir.switch op.
mlir::Block *exitBlock = rewriter.splitBlock(
rewriter.getBlock(), op->getNextNode()->getIterator());
Expand All @@ -322,6 +323,18 @@ class CIRSwitchOpFlattening : public mlir::OpRewritePattern<cir::SwitchOp> {
// 3. Replace the empty cir.switch.op with the new cir.switchflat op by the
// recorded block and conditions.

// First we have to handle the rewrite of all of the 'break' ops to make
// sure they now go to the right place, including the ones in the pre-case
// blcoks.
walkRegionSkipping<cir::LoopOpInterface, cir::SwitchOp>(
op.getBody(), [&](mlir::Operation *op) {
if (!isa<cir::BreakOp>(op))
return mlir::WalkResult::advance();

lowerTerminator(op, exitBlock, rewriter);
return mlir::WalkResult::skip();
});

// inline everything from switch body between the switch op and the exit
// block.
{
Expand Down Expand Up @@ -389,16 +402,6 @@ class CIRSwitchOpFlattening : public mlir::OpRewritePattern<cir::SwitchOp> {
break;
}

// Handle break statements.
walkRegionSkipping<cir::LoopOpInterface, cir::SwitchOp>(
region, [&](mlir::Operation *op) {
if (!isa<cir::BreakOp>(op))
return mlir::WalkResult::advance();

lowerTerminator(op, exitBlock, rewriter);
return mlir::WalkResult::skip();
});

// Track fallthrough in cases.
for (mlir::Block &blk : region.getBlocks()) {
if (blk.getNumSuccessors())
Expand Down
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