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Merged
merged 4 commits into from
May 22, 2025
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[CIR] Implement switch case simplify #140649

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c1403f1
Implement CIR switch case simplify with appropriate tests
Andres-Salamanca May 19, 2025
0afcfd6
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Andres-Salamanca May 21, 2025
e46e3ab
Fix formatting
Andres-Salamanca May 21, 2025
be257c5
Remove curly braces
Andres-Salamanca May 21, 2025
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1 change: 0 additions & 1 deletion clang/include/clang/CIR/MissingFeatures.h
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Original file line number Diff line number Diff line change
Expand Up @@ -114,7 +114,6 @@ struct MissingFeatures {
static bool opUnaryPromotionType() { return false; }

// SwitchOp handling
static bool foldCascadingCases() { return false; }
static bool foldRangeCase() { return false; }

// Clang early optimizations or things defered to LLVM lowering.
Expand Down
6 changes: 0 additions & 6 deletions clang/lib/CIR/CodeGen/CIRGenStmt.cpp
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Expand Up @@ -531,12 +531,6 @@ mlir::LogicalResult CIRGenFunction::emitCaseStmt(const CaseStmt &s,
value = builder.getArrayAttr({cir::IntAttr::get(condType, intVal),
cir::IntAttr::get(condType, endVal)});
kind = cir::CaseOpKind::Range;

// We don't currently fold case range statements with other case statements.
// TODO(cir): Add this capability. Folding these cases is going to be
// implemented in CIRSimplify when it is upstreamed.
assert(!cir::MissingFeatures::foldRangeCase());
assert(!cir::MissingFeatures::foldCascadingCases());
} else {
value = builder.getArrayAttr({cir::IntAttr::get(condType, intVal)});
kind = cir::CaseOpKind::Equal;
Expand Down
106 changes: 104 additions & 2 deletions clang/lib/CIR/Dialect/Transforms/CIRSimplify.cpp
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Expand Up @@ -159,6 +159,107 @@ struct SimplifySelect : public OpRewritePattern<SelectOp> {
}
};

/// Simplify `cir.switch` operations by folding cascading cases
/// into a single `cir.case` with the `anyof` kind.
///
/// This pattern identifies cascading cases within a `cir.switch` operation.
/// Cascading cases are defined as consecutive `cir.case` operations of kind
/// `equal`, each containing a single `cir.yield` operation in their body.
///
/// The pattern merges these cascading cases into a single `cir.case` operation
/// with kind `anyof`, aggregating all the case values.
///
/// The merging process continues until a `cir.case` with a different body
/// (e.g., containing `cir.break` or compound stmt) is encountered, which
/// breaks the chain.
///
/// Example:
///
/// Before:
/// cir.case equal, [#cir.int<0> : !s32i] {
/// cir.yield
/// }
/// cir.case equal, [#cir.int<1> : !s32i] {
/// cir.yield
/// }
/// cir.case equal, [#cir.int<2> : !s32i] {
/// cir.break
/// }
///
/// After applying SimplifySwitch:
/// cir.case anyof, [#cir.int<0> : !s32i, #cir.int<1> : !s32i, #cir.int<2> :
/// !s32i] {
/// cir.break
/// }
struct SimplifySwitch : public OpRewritePattern<SwitchOp> {
using OpRewritePattern<SwitchOp>::OpRewritePattern;
LogicalResult matchAndRewrite(SwitchOp op,
PatternRewriter &rewriter) const override {

LogicalResult changed = mlir::failure();
SmallVector<CaseOp, 8> cases;
SmallVector<CaseOp, 4> cascadingCases;
SmallVector<mlir::Attribute, 4> cascadingCaseValues;

op.collectCases(cases);
if (cases.empty())
return mlir::failure();

auto flushMergedOps = [&]() {
for (CaseOp &c : cascadingCases)
rewriter.eraseOp(c);
cascadingCases.clear();
cascadingCaseValues.clear();
};

auto mergeCascadingInto = [&](CaseOp &target) {
rewriter.modifyOpInPlace(target, [&]() {
target.setValueAttr(rewriter.getArrayAttr(cascadingCaseValues));
target.setKind(CaseOpKind::Anyof);
});
changed = mlir::success();
};

for (CaseOp c : cases) {
cir::CaseOpKind kind = c.getKind();
if (kind == cir::CaseOpKind::Equal &&
isa<YieldOp>(c.getCaseRegion().front().front())) {
// If the case contains only a YieldOp, collect it for cascading merge
cascadingCases.push_back(c);
cascadingCaseValues.push_back(c.getValue()[0]);
} else if (kind == cir::CaseOpKind::Equal && !cascadingCases.empty()) {
// merge previously collected cascading cases
cascadingCaseValues.push_back(c.getValue()[0]);
mergeCascadingInto(c);
flushMergedOps();
} else if (kind != cir::CaseOpKind::Equal && cascadingCases.size() > 1) {
// If a Default, Anyof or Range case is found and there are previous
// cascading cases, merge all of them into the last cascading case.
// We don't currently fold case range statements with other case
// statements.
assert(!cir::MissingFeatures::foldRangeCase());
CaseOp lastCascadingCase = cascadingCases.back();
mergeCascadingInto(lastCascadingCase);
cascadingCases.pop_back();
flushMergedOps();
} else {
cascadingCases.clear();
cascadingCaseValues.clear();
}
}

// Edge case: all cases are simple cascading cases
if (cascadingCases.size() == cases.size()) {
CaseOp lastCascadingCase = cascadingCases.back();
mergeCascadingInto(lastCascadingCase);
cascadingCases.pop_back();
flushMergedOps();
}

return changed;
}
};

//===----------------------------------------------------------------------===//
// CIRSimplifyPass
//===----------------------------------------------------------------------===//
Expand All @@ -173,7 +274,8 @@ void populateMergeCleanupPatterns(RewritePatternSet &patterns) {
// clang-format off
patterns.add<
SimplifyTernary,
SimplifySelect
SimplifySelect,
SimplifySwitch
>(patterns.getContext());
// clang-format on
}
Expand All @@ -186,7 +288,7 @@ void CIRSimplifyPass::runOnOperation() {
// Collect operations to apply patterns.
llvm::SmallVector<Operation *, 16> ops;
getOperation()->walk([&](Operation *op) {
if (isa<TernaryOp, SelectOp>(op))
if (isa<TernaryOp, SelectOp, SwitchOp>(op))
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Can you double check if the test passes without issues if -DMLIR_ENABLE_EXPENSIVE_PATTERN_API_CHECKS=ON is used while building clang? We currently having incubator issues with this and probably best to make sure we don't introduce them here if possible.

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I have built Clang with the -DMLIR_ENABLE_EXPENSIVE_PATTERN_API_CHECKS=ON flag, and this pull request passes successfully. However, I have identified two failing tests:


********************
Failed Tests (2):
  Clang :: CIR/CodeGen/loop.cpp
  Clang :: CIR/Transforms/switch.cir
********************

The CIR/Transforms/switch.cir test fails when applying the -cir-flatten-cfg pass. I'm going to check if this test is also failing in the incubator.

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Just checked and it also fails in the incubator.

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Thanks for walking the extra leg here, can you create an issue for this so we can take a look later? (cc @xlauko which pointed this recently).

ops.push_back(op);
});

Expand Down
196 changes: 196 additions & 0 deletions clang/test/CIR/Transforms/switch-fold.cir
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@@ -0,0 +1,196 @@
// RUN: cir-opt -cir-canonicalize -cir-simplify -o %t.cir %s
// RUN: FileCheck --input-file=%t.cir %s

!s32i = !cir.int<s, 32>

module {
cir.func @foldCascade(%arg0: !s32i) {
%0 = cir.alloca !s32i, !cir.ptr<!s32i>, ["a", init] {alignment = 4 : i64}
cir.store %arg0, %0 : !s32i, !cir.ptr<!s32i>
cir.scope {
%1 = cir.load %0 : !cir.ptr<!s32i>, !s32i
cir.switch (%1 : !s32i) {
cir.case(equal, [#cir.int<1> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<2> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<3> : !s32i]) {
%2 = cir.const #cir.int<2> : !s32i
cir.store %2, %0 : !s32i, !cir.ptr<!s32i>
cir.break
}
cir.yield
}
}
cir.return
}
//CHECK: cir.func @foldCascade
//CHECK: cir.switch (%[[COND:.*]] : !s32i) {
//CHECK-NEXT: cir.case(anyof, [#cir.int<1> : !s32i, #cir.int<2> : !s32i, #cir.int<3> : !s32i]) {
//CHECK-NEXT: %[[TWO:.*]] = cir.const #cir.int<2> : !s32i
//CHECK-NEXT: cir.store %[[TWO]], %[[ARG0:.*]] : !s32i, !cir.ptr<!s32i>
//CHECK-NEXT: cir.break
//CHECK-NEXT: }
//CHECK-NEXT: cir.yield
//CHECK-NEXT: }

cir.func @foldCascade2(%arg0: !s32i) {
%0 = cir.alloca !s32i, !cir.ptr<!s32i>, ["a", init] {alignment = 4 : i64}
cir.store %arg0, %0 : !s32i, !cir.ptr<!s32i>
cir.scope {
%1 = cir.load %0 : !cir.ptr<!s32i>, !s32i
cir.switch (%1 : !s32i) {
cir.case(equal, [#cir.int<0> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<2> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<4> : !s32i]) {
cir.break
}
cir.case(equal, [#cir.int<1> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<3> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<5> : !s32i]) {
cir.break
}
cir.yield
}
}
cir.return
}
//CHECK: @foldCascade2
//CHECK: cir.switch (%[[COND2:.*]] : !s32i) {
//CHECK: cir.case(anyof, [#cir.int<0> : !s32i, #cir.int<2> : !s32i, #cir.int<4> : !s32i]) {
//CHECK: cir.break
//cehck: }
//CHECK: cir.case(anyof, [#cir.int<1> : !s32i, #cir.int<3> : !s32i, #cir.int<5> : !s32i]) {
//CHECK: cir.break
//CHECK: }
//CHECK: cir.yield
//CHECK: }
cir.func @foldCascade3(%arg0: !s32i ) {
%0 = cir.alloca !s32i, !cir.ptr<!s32i>, ["a", init] {alignment = 4 : i64}
cir.store %arg0, %0 : !s32i, !cir.ptr<!s32i>
cir.scope {
%1 = cir.alloca !s32i, !cir.ptr<!s32i>, ["x"] {alignment = 4 : i64}
%2 = cir.load %0 : !cir.ptr<!s32i>, !s32i
cir.switch (%2 : !s32i) {
cir.case(equal, [#cir.int<0> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<1> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<2> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<3> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<4> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<5> : !s32i]) {
cir.break
}
cir.yield
}
}
cir.return
}
//CHECK: cir.func @foldCascade3
//CHECK: cir.switch (%[[COND3:.*]] : !s32i) {
//CHECK: cir.case(anyof, [#cir.int<0> : !s32i, #cir.int<1> : !s32i, #cir.int<2> : !s32i, #cir.int<3> : !s32i, #cir.int<4> : !s32i, #cir.int<5> : !s32i]) {
//CHECK: cir.break
//CHECK: }
//CHECK: cir.yield
//CHECK: }
cir.func @foldCascadeWithDefault(%arg0: !s32i ) {
%0 = cir.alloca !s32i, !cir.ptr<!s32i>, ["a", init] {alignment = 4 : i64}
cir.store %arg0, %0 : !s32i, !cir.ptr<!s32i>
cir.scope {
%1 = cir.load %0 : !cir.ptr<!s32i>, !s32i
cir.switch (%1 : !s32i) {
cir.case(equal, [#cir.int<3> : !s32i]) {
cir.break
}
cir.case(equal, [#cir.int<4> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<5> : !s32i]) {
cir.yield
}
cir.case(default, []) {
cir.yield
}
cir.case(equal, [#cir.int<6> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<7> : !s32i]) {
cir.break
}
cir.yield
}
}
cir.return
}
//CHECK: cir.func @foldCascadeWithDefault
//CHECK: cir.switch (%[[COND:.*]] : !s32i) {
//CHECK: cir.case(equal, [#cir.int<3> : !s32i]) {
//CHECK: cir.break
//CHECK: }
//CHECK: cir.case(anyof, [#cir.int<4> : !s32i, #cir.int<5> : !s32i]) {
//CHECK: cir.yield
//CHECK: }
//CHECK: cir.case(default, []) {
//CHECK: cir.yield
//CHECK: }
//CHECK: cir.case(anyof, [#cir.int<6> : !s32i, #cir.int<7> : !s32i]) {
//CHECK: cir.break
//CHECK: }
//CHECK: cir.yield
//CHECK: }
cir.func @foldAllCascade(%arg0: !s32i ) {
%0 = cir.alloca !s32i, !cir.ptr<!s32i>, ["a", init] {alignment = 4 : i64}
cir.store %arg0, %0 : !s32i, !cir.ptr<!s32i>
cir.scope {
%1 = cir.load %0 : !cir.ptr<!s32i>, !s32i
cir.switch (%1 : !s32i) {
cir.case(equal, [#cir.int<0> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<1> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<2> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<3> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<4> : !s32i]) {
cir.yield
}
cir.case(equal, [#cir.int<5> : !s32i]) {
cir.yield
}
cir.yield
}
}
cir.return
}
//CHECK: cir.func @foldAllCascade
//CHECK: cir.switch (%[[COND:.*]] : !s32i) {
//CHECK: cir.case(anyof, [#cir.int<0> : !s32i, #cir.int<1> : !s32i, #cir.int<2> : !s32i, #cir.int<3> : !s32i, #cir.int<4> : !s32i, #cir.int<5> : !s32i]) {
//CHECK: cir.yield
//CHECK: }
//CHECK: cir.yield
//CHECK: }
}