[CIR] Upstream LabelOp #152802

Andres-Salamanca · 2025-08-08T21:34:21Z

This PR introduces the LabelOp, which is required for implementing GotoOp lowering in the future.
Lowering to LLVM IR is not included in this patch, since it depends on the upcoming GotoSolver.

The GotoSolver traverses the function body, and if it finds a LabelOp without a matching GotoOp, it erases the label.
This means our implementation differs from the classic codegen approach, where labels may be retained even if unused.

Example:
https://godbolt.org/z/37Mvr4MMr

llvmbot · 2025-08-08T21:34:52Z

@llvm/pr-subscribers-clang

Author: None (Andres-Salamanca)

Changes

This PR introduces the LabelOp, which is required for implementing GotoOp lowering in the future.
Lowering to LLVM IR is not included in this patch, since it depends on the upcoming GotoSolver.

The GotoSolver traverses the function body, and if it finds a LabelOp without a matching GotoOp, it erases the label.
This means our implementation differs from the classic codegen approach, where labels may be retained even if unused.

Example:
https://godbolt.org/z/37Mvr4MMr

Full diff: https://github.com/llvm/llvm-project/pull/152802.diff

7 Files Affected:

(modified) clang/include/clang/CIR/Dialect/IR/CIROps.td (+14)
(modified) clang/lib/CIR/CodeGen/CIRGenFunction.h (+3)
(modified) clang/lib/CIR/CodeGen/CIRGenStmt.cpp (+40)
(modified) clang/lib/CIR/Dialect/IR/CIRDialect.cpp (+13)
(modified) clang/lib/CIR/Dialect/Transforms/CIRCanonicalize.cpp (+2-2)
(added) clang/test/CIR/CodeGen/label.c (+65)
(added) clang/test/CIR/IR/label.cir (+26)

diff --git a/clang/include/clang/CIR/Dialect/IR/CIROps.td b/clang/include/clang/CIR/Dialect/IR/CIROps.td
index 72841a1c08441..bb16a75457ff5 100644
--- a/clang/include/clang/CIR/Dialect/IR/CIROps.td
+++ b/clang/include/clang/CIR/Dialect/IR/CIROps.td
@@ -1060,6 +1060,20 @@ def CIR_BrOp : CIR_Op<"br",[
   }];
 }
 
+//===----------------------------------------------------------------------===//
+// LabelOp
+//===----------------------------------------------------------------------===//
+
+// The LabelOp has AlwaysSpeculatable trait in order to not to be swept by canonicalizer
+def CIR_LabelOp : CIR_Op<"label", [AlwaysSpeculatable]> {
+  let description = [{
+    An identifier which may be referred by cir.goto operation
+  }];
+  let arguments = (ins StrAttr:$label);
+  let assemblyFormat = [{ $label attr-dict }];
+  let hasVerifier = 1;
+}
+
 //===----------------------------------------------------------------------===//
 // UnaryOp
 //===----------------------------------------------------------------------===//
diff --git a/clang/lib/CIR/CodeGen/CIRGenFunction.h b/clang/lib/CIR/CodeGen/CIRGenFunction.h
index 2e60cfc8211e6..d2e9c163d7f79 100644
--- a/clang/lib/CIR/CodeGen/CIRGenFunction.h
+++ b/clang/lib/CIR/CodeGen/CIRGenFunction.h
@@ -1125,6 +1125,9 @@ class CIRGenFunction : public CIRGenTypeCache {
 
   mlir::Value emitOpOnBoolExpr(mlir::Location loc, const clang::Expr *cond);
 
+  mlir::LogicalResult emitLabel(const clang::LabelDecl *d);
+  mlir::LogicalResult emitLabelStmt(const clang::LabelStmt &s);
+
   mlir::LogicalResult emitIfStmt(const clang::IfStmt &s);
 
   /// Emit code to compute the specified expression,
diff --git a/clang/lib/CIR/CodeGen/CIRGenStmt.cpp b/clang/lib/CIR/CodeGen/CIRGenStmt.cpp
index 50642e7ca48d7..49d1800aa15e5 100644
--- a/clang/lib/CIR/CodeGen/CIRGenStmt.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenStmt.cpp
@@ -256,6 +256,9 @@ mlir::LogicalResult CIRGenFunction::emitSimpleStmt(const Stmt *s,
   // NullStmt doesn't need any handling, but we need to say we handled it.
   case Stmt::NullStmtClass:
     break;
+
+  case Stmt::LabelStmtClass:
+    return emitLabelStmt(cast<LabelStmt>(*s));
   case Stmt::CaseStmtClass:
   case Stmt::DefaultStmtClass:
     // If we reached here, we must not handling a switch case in the top level.
@@ -272,6 +275,17 @@ mlir::LogicalResult CIRGenFunction::emitSimpleStmt(const Stmt *s,
   return mlir::success();
 }
 
+mlir::LogicalResult CIRGenFunction::emitLabelStmt(const clang::LabelStmt &s) {
+
+  if (emitLabel(s.getDecl()).failed())
+    return mlir::failure();
+
+  // IsEHa: not implemented.
+  assert(!(getContext().getLangOpts().EHAsynch && s.isSideEntry()));
+
+  return emitStmt(s.getSubStmt(), /*useCurrentScope*/ true);
+}
+
 // Add a terminating yield on a body region if no other terminators are used.
 static void terminateBody(CIRGenBuilderTy &builder, mlir::Region &r,
                           mlir::Location loc) {
@@ -429,6 +443,32 @@ CIRGenFunction::emitContinueStmt(const clang::ContinueStmt &s) {
   return mlir::success();
 }
 
+mlir::LogicalResult CIRGenFunction::emitLabel(const clang::LabelDecl *d) {
+  // Create a new block to tag with a label and add a branch from
+  // the current one to it. If the block is empty just call attach it
+  // to this label.
+  mlir::Block *currBlock = builder.getBlock();
+  mlir::Block *labelBlock = currBlock;
+
+  if (!currBlock->empty()) {
+    {
+      mlir::OpBuilder::InsertionGuard guard(builder);
+      labelBlock = builder.createBlock(builder.getBlock()->getParent());
+    }
+    builder.create<cir::BrOp>(getLoc(d->getSourceRange()), labelBlock);
+  }
+
+  builder.setInsertionPointToEnd(labelBlock);
+  builder.create<cir::LabelOp>(getLoc(d->getSourceRange()), d->getName());
+  builder.setInsertionPointToEnd(labelBlock);
+
+  //  FIXME: emit debug info for labels, incrementProfileCounter
+  assert(!cir::MissingFeatures::ehstackBranches());
+  assert(!cir::MissingFeatures::incrementProfileCounter());
+  assert(!cir::MissingFeatures::generateDebugInfo());
+  return mlir::success();
+}
+
 mlir::LogicalResult CIRGenFunction::emitBreakStmt(const clang::BreakStmt &s) {
   builder.createBreak(getLoc(s.getBreakLoc()));
 
diff --git a/clang/lib/CIR/Dialect/IR/CIRDialect.cpp b/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
index d3fcac1edeb5a..32029f8f9b49b 100644
--- a/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
+++ b/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
@@ -1762,6 +1762,19 @@ LogicalResult cir::ShiftOp::verify() {
   return mlir::success();
 }
 
+//===----------------------------------------------------------------------===//
+// LabelOp Definitions
+//===----------------------------------------------------------------------===//
+
+LogicalResult cir::LabelOp::verify() {
+  mlir::Operation *op = getOperation();
+  mlir::Block *blk = op->getBlock();
+  if (&blk->front() != op)
+    return emitError() << "must be the first operation in a block";
+
+  return mlir::success();
+}
+
 //===----------------------------------------------------------------------===//
 // UnaryOp
 //===----------------------------------------------------------------------===//
diff --git a/clang/lib/CIR/Dialect/Transforms/CIRCanonicalize.cpp b/clang/lib/CIR/Dialect/Transforms/CIRCanonicalize.cpp
index 2eaa60c631a12..d41ea0af58938 100644
--- a/clang/lib/CIR/Dialect/Transforms/CIRCanonicalize.cpp
+++ b/clang/lib/CIR/Dialect/Transforms/CIRCanonicalize.cpp
@@ -47,8 +47,8 @@ struct RemoveRedundantBranches : public OpRewritePattern<BrOp> {
     Block *block = op.getOperation()->getBlock();
     Block *dest = op.getDest();
 
-    assert(!cir::MissingFeatures::labelOp());
-
+    if (isa<cir::LabelOp>(dest->front()))
+      return failure();
     // Single edge between blocks: merge it.
     if (block->getNumSuccessors() == 1 &&
         dest->getSinglePredecessor() == block) {
diff --git a/clang/test/CIR/CodeGen/label.c b/clang/test/CIR/CodeGen/label.c
new file mode 100644
index 0000000000000..08db95a1392cb
--- /dev/null
+++ b/clang/test/CIR/CodeGen/label.c
@@ -0,0 +1,65 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s --check-prefix=CIR
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s --check-prefix=OGCG
+
+void label() {
+labelA:
+  return;
+}
+
+// CIR:  cir.func no_proto dso_local @label
+// CIR:    cir.label "labelA"
+// CIR:    cir.return
+
+// OGCG: define dso_local void @label
+// OGCG:   br label %labelA
+// OGCG: labelA:
+// OGCG:   ret void
+
+void multiple_labels() {
+labelB:
+labelC:
+  return;
+}
+
+// CIR:  cir.func no_proto dso_local @multiple_labels
+// CIR:    cir.label "labelB"
+// CIR:    cir.br ^bb1
+// CIR:  ^bb1:  // pred: ^bb0
+// CIR:    cir.label "labelC"
+// CIR:    cir.return
+
+// OGCG: define dso_local void @multiple_labels
+// OGCG:   br label %labelB
+// OGCG: labelB:
+// OGCG:   br label %labelC
+// OGCG: labelC:
+// OGCG:   ret void
+
+void label_in_if(int cond) {
+  if (cond) {
+labelD:
+    cond++;
+  }
+}
+
+// CIR:  cir.func dso_local @label_in_if
+// CIR:      cir.if {{.*}} {
+// CIR:        cir.label "labelD"
+// CIR:        [[LOAD:%.*]] = cir.load align(4) [[COND:%.*]] : !cir.ptr<!s32i>, !s32i
+// CIR:        [[INC:%.*]] = cir.unary(inc, %3) nsw : !s32i, !s32i
+// CIR:        cir.store align(4) [[INC]], [[COND]] : !s32i, !cir.ptr<!s32i>
+// CIR:      }
+// CIR:    cir.return
+
+// OGCG: define dso_local void @label_in_if
+// OGCG: if.then:
+// OGCG:   br label %labelD
+// OGCG: labelD:
+// OGCG:   [[LOAD:%.*]] = load i32, ptr [[COND:%.*]], align 4
+// OGCG:   [[INC:%.*]] = add nsw i32 %1, 1
+// OGCG:   store i32 [[INC]], ptr [[COND]], align 4
+// OGCG:   br label %if.end
+// OGCG: if.end:
+// OGCG:   ret void
diff --git a/clang/test/CIR/IR/label.cir b/clang/test/CIR/IR/label.cir
new file mode 100644
index 0000000000000..2211a4e8da331
--- /dev/null
+++ b/clang/test/CIR/IR/label.cir
@@ -0,0 +1,26 @@
+// RUN: cir-opt %s | FileCheck %s
+
+!s32i = !cir.int<s, 32>
+
+module  {
+  cir.func @label() {
+    cir.label "label"
+    cir.return
+  }
+
+  cir.func @label2() {
+    %0 = cir.const #cir.int<0> : !s32i
+    cir.br ^bb1
+  ^bb1:  // pred: ^bb0
+    cir.label "label2"
+    cir.return
+  }
+}
+
+// CHECK:       cir.func @label
+// CHECK-NEXT:    cir.label "label"
+
+// CHECK:       cir.func @label2
+// CHECK:        cir.br ^bb1
+// CHECK-NEXT:  ^bb1:  // pred: ^bb0
+// CHECK-NEXT:    cir.label "label2"

llvmbot · 2025-08-08T21:34:53Z

@llvm/pr-subscribers-clangir

Author: None (Andres-Salamanca)

Changes

This PR introduces the LabelOp, which is required for implementing GotoOp lowering in the future.
Lowering to LLVM IR is not included in this patch, since it depends on the upcoming GotoSolver.

The GotoSolver traverses the function body, and if it finds a LabelOp without a matching GotoOp, it erases the label.
This means our implementation differs from the classic codegen approach, where labels may be retained even if unused.

Example:
https://godbolt.org/z/37Mvr4MMr

Full diff: https://github.com/llvm/llvm-project/pull/152802.diff

7 Files Affected:

(modified) clang/include/clang/CIR/Dialect/IR/CIROps.td (+14)
(modified) clang/lib/CIR/CodeGen/CIRGenFunction.h (+3)
(modified) clang/lib/CIR/CodeGen/CIRGenStmt.cpp (+40)
(modified) clang/lib/CIR/Dialect/IR/CIRDialect.cpp (+13)
(modified) clang/lib/CIR/Dialect/Transforms/CIRCanonicalize.cpp (+2-2)
(added) clang/test/CIR/CodeGen/label.c (+65)
(added) clang/test/CIR/IR/label.cir (+26)

diff --git a/clang/include/clang/CIR/Dialect/IR/CIROps.td b/clang/include/clang/CIR/Dialect/IR/CIROps.td
index 72841a1c08441..bb16a75457ff5 100644
--- a/clang/include/clang/CIR/Dialect/IR/CIROps.td
+++ b/clang/include/clang/CIR/Dialect/IR/CIROps.td
@@ -1060,6 +1060,20 @@ def CIR_BrOp : CIR_Op<"br",[
   }];
 }
 
+//===----------------------------------------------------------------------===//
+// LabelOp
+//===----------------------------------------------------------------------===//
+
+// The LabelOp has AlwaysSpeculatable trait in order to not to be swept by canonicalizer
+def CIR_LabelOp : CIR_Op<"label", [AlwaysSpeculatable]> {
+  let description = [{
+    An identifier which may be referred by cir.goto operation
+  }];
+  let arguments = (ins StrAttr:$label);
+  let assemblyFormat = [{ $label attr-dict }];
+  let hasVerifier = 1;
+}
+
 //===----------------------------------------------------------------------===//
 // UnaryOp
 //===----------------------------------------------------------------------===//
diff --git a/clang/lib/CIR/CodeGen/CIRGenFunction.h b/clang/lib/CIR/CodeGen/CIRGenFunction.h
index 2e60cfc8211e6..d2e9c163d7f79 100644
--- a/clang/lib/CIR/CodeGen/CIRGenFunction.h
+++ b/clang/lib/CIR/CodeGen/CIRGenFunction.h
@@ -1125,6 +1125,9 @@ class CIRGenFunction : public CIRGenTypeCache {
 
   mlir::Value emitOpOnBoolExpr(mlir::Location loc, const clang::Expr *cond);
 
+  mlir::LogicalResult emitLabel(const clang::LabelDecl *d);
+  mlir::LogicalResult emitLabelStmt(const clang::LabelStmt &s);
+
   mlir::LogicalResult emitIfStmt(const clang::IfStmt &s);
 
   /// Emit code to compute the specified expression,
diff --git a/clang/lib/CIR/CodeGen/CIRGenStmt.cpp b/clang/lib/CIR/CodeGen/CIRGenStmt.cpp
index 50642e7ca48d7..49d1800aa15e5 100644
--- a/clang/lib/CIR/CodeGen/CIRGenStmt.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenStmt.cpp
@@ -256,6 +256,9 @@ mlir::LogicalResult CIRGenFunction::emitSimpleStmt(const Stmt *s,
   // NullStmt doesn't need any handling, but we need to say we handled it.
   case Stmt::NullStmtClass:
     break;
+
+  case Stmt::LabelStmtClass:
+    return emitLabelStmt(cast<LabelStmt>(*s));
   case Stmt::CaseStmtClass:
   case Stmt::DefaultStmtClass:
     // If we reached here, we must not handling a switch case in the top level.
@@ -272,6 +275,17 @@ mlir::LogicalResult CIRGenFunction::emitSimpleStmt(const Stmt *s,
   return mlir::success();
 }
 
+mlir::LogicalResult CIRGenFunction::emitLabelStmt(const clang::LabelStmt &s) {
+
+  if (emitLabel(s.getDecl()).failed())
+    return mlir::failure();
+
+  // IsEHa: not implemented.
+  assert(!(getContext().getLangOpts().EHAsynch && s.isSideEntry()));
+
+  return emitStmt(s.getSubStmt(), /*useCurrentScope*/ true);
+}
+
 // Add a terminating yield on a body region if no other terminators are used.
 static void terminateBody(CIRGenBuilderTy &builder, mlir::Region &r,
                           mlir::Location loc) {
@@ -429,6 +443,32 @@ CIRGenFunction::emitContinueStmt(const clang::ContinueStmt &s) {
   return mlir::success();
 }
 
+mlir::LogicalResult CIRGenFunction::emitLabel(const clang::LabelDecl *d) {
+  // Create a new block to tag with a label and add a branch from
+  // the current one to it. If the block is empty just call attach it
+  // to this label.
+  mlir::Block *currBlock = builder.getBlock();
+  mlir::Block *labelBlock = currBlock;
+
+  if (!currBlock->empty()) {
+    {
+      mlir::OpBuilder::InsertionGuard guard(builder);
+      labelBlock = builder.createBlock(builder.getBlock()->getParent());
+    }
+    builder.create<cir::BrOp>(getLoc(d->getSourceRange()), labelBlock);
+  }
+
+  builder.setInsertionPointToEnd(labelBlock);
+  builder.create<cir::LabelOp>(getLoc(d->getSourceRange()), d->getName());
+  builder.setInsertionPointToEnd(labelBlock);
+
+  //  FIXME: emit debug info for labels, incrementProfileCounter
+  assert(!cir::MissingFeatures::ehstackBranches());
+  assert(!cir::MissingFeatures::incrementProfileCounter());
+  assert(!cir::MissingFeatures::generateDebugInfo());
+  return mlir::success();
+}
+
 mlir::LogicalResult CIRGenFunction::emitBreakStmt(const clang::BreakStmt &s) {
   builder.createBreak(getLoc(s.getBreakLoc()));
 
diff --git a/clang/lib/CIR/Dialect/IR/CIRDialect.cpp b/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
index d3fcac1edeb5a..32029f8f9b49b 100644
--- a/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
+++ b/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
@@ -1762,6 +1762,19 @@ LogicalResult cir::ShiftOp::verify() {
   return mlir::success();
 }
 
+//===----------------------------------------------------------------------===//
+// LabelOp Definitions
+//===----------------------------------------------------------------------===//
+
+LogicalResult cir::LabelOp::verify() {
+  mlir::Operation *op = getOperation();
+  mlir::Block *blk = op->getBlock();
+  if (&blk->front() != op)
+    return emitError() << "must be the first operation in a block";
+
+  return mlir::success();
+}
+
 //===----------------------------------------------------------------------===//
 // UnaryOp
 //===----------------------------------------------------------------------===//
diff --git a/clang/lib/CIR/Dialect/Transforms/CIRCanonicalize.cpp b/clang/lib/CIR/Dialect/Transforms/CIRCanonicalize.cpp
index 2eaa60c631a12..d41ea0af58938 100644
--- a/clang/lib/CIR/Dialect/Transforms/CIRCanonicalize.cpp
+++ b/clang/lib/CIR/Dialect/Transforms/CIRCanonicalize.cpp
@@ -47,8 +47,8 @@ struct RemoveRedundantBranches : public OpRewritePattern<BrOp> {
     Block *block = op.getOperation()->getBlock();
     Block *dest = op.getDest();
 
-    assert(!cir::MissingFeatures::labelOp());
-
+    if (isa<cir::LabelOp>(dest->front()))
+      return failure();
     // Single edge between blocks: merge it.
     if (block->getNumSuccessors() == 1 &&
         dest->getSinglePredecessor() == block) {
diff --git a/clang/test/CIR/CodeGen/label.c b/clang/test/CIR/CodeGen/label.c
new file mode 100644
index 0000000000000..08db95a1392cb
--- /dev/null
+++ b/clang/test/CIR/CodeGen/label.c
@@ -0,0 +1,65 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s --check-prefix=CIR
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s --check-prefix=OGCG
+
+void label() {
+labelA:
+  return;
+}
+
+// CIR:  cir.func no_proto dso_local @label
+// CIR:    cir.label "labelA"
+// CIR:    cir.return
+
+// OGCG: define dso_local void @label
+// OGCG:   br label %labelA
+// OGCG: labelA:
+// OGCG:   ret void
+
+void multiple_labels() {
+labelB:
+labelC:
+  return;
+}
+
+// CIR:  cir.func no_proto dso_local @multiple_labels
+// CIR:    cir.label "labelB"
+// CIR:    cir.br ^bb1
+// CIR:  ^bb1:  // pred: ^bb0
+// CIR:    cir.label "labelC"
+// CIR:    cir.return
+
+// OGCG: define dso_local void @multiple_labels
+// OGCG:   br label %labelB
+// OGCG: labelB:
+// OGCG:   br label %labelC
+// OGCG: labelC:
+// OGCG:   ret void
+
+void label_in_if(int cond) {
+  if (cond) {
+labelD:
+    cond++;
+  }
+}
+
+// CIR:  cir.func dso_local @label_in_if
+// CIR:      cir.if {{.*}} {
+// CIR:        cir.label "labelD"
+// CIR:        [[LOAD:%.*]] = cir.load align(4) [[COND:%.*]] : !cir.ptr<!s32i>, !s32i
+// CIR:        [[INC:%.*]] = cir.unary(inc, %3) nsw : !s32i, !s32i
+// CIR:        cir.store align(4) [[INC]], [[COND]] : !s32i, !cir.ptr<!s32i>
+// CIR:      }
+// CIR:    cir.return
+
+// OGCG: define dso_local void @label_in_if
+// OGCG: if.then:
+// OGCG:   br label %labelD
+// OGCG: labelD:
+// OGCG:   [[LOAD:%.*]] = load i32, ptr [[COND:%.*]], align 4
+// OGCG:   [[INC:%.*]] = add nsw i32 %1, 1
+// OGCG:   store i32 [[INC]], ptr [[COND]], align 4
+// OGCG:   br label %if.end
+// OGCG: if.end:
+// OGCG:   ret void
diff --git a/clang/test/CIR/IR/label.cir b/clang/test/CIR/IR/label.cir
new file mode 100644
index 0000000000000..2211a4e8da331
--- /dev/null
+++ b/clang/test/CIR/IR/label.cir
@@ -0,0 +1,26 @@
+// RUN: cir-opt %s | FileCheck %s
+
+!s32i = !cir.int<s, 32>
+
+module  {
+  cir.func @label() {
+    cir.label "label"
+    cir.return
+  }
+
+  cir.func @label2() {
+    %0 = cir.const #cir.int<0> : !s32i
+    cir.br ^bb1
+  ^bb1:  // pred: ^bb0
+    cir.label "label2"
+    cir.return
+  }
+}
+
+// CHECK:       cir.func @label
+// CHECK-NEXT:    cir.label "label"
+
+// CHECK:       cir.func @label2
+// CHECK:        cir.br ^bb1
+// CHECK-NEXT:  ^bb1:  // pred: ^bb0
+// CHECK-NEXT:    cir.label "label2"

mmha · 2025-08-11T12:23:36Z

Can you add tests where you put a label in some unreachable code?

void after_return() {
  return;
  label:
}

void after_throw() {
  throw 0;
  label:
}

void after_unreachable() {
  __builtin_unreachable();
  label:
}

These would be more interesting once we have goto but it's good to have them now.

mmha

LGTM

mmha · 2025-08-11T12:34:00Z

clang/lib/CIR/CodeGen/CIRGenFunction.h

+  mlir::LogicalResult emitLabel(const clang::LabelDecl *d);
+  mlir::LogicalResult emitLabelStmt(const clang::LabelStmt &s);


No action for you here, but we are pretty inconsistent with pass-by-pointer vs. pass-by-reference for emit* functions.

It's true. These signatures follow the equivalents in OGCG, which is likewise inconsistent. (Not that that's a good excuse for propagating the inconsistency.)

yea, probably worth picking just one for this PR.

mmha · 2025-08-11T12:36:13Z

clang/lib/CIR/CodeGen/CIRGenStmt.cpp

+  if (emitLabel(s.getDecl()).failed())
+    return mlir::failure();
+
+  // IsEHa: not implemented.


Can you make this a errorNYI?

mmha · 2025-08-11T13:06:24Z

clang/lib/CIR/CodeGen/CIRGenStmt.cpp

 }

+mlir::LogicalResult CIRGenFunction::emitLabel(const clang::LabelDecl *d) {
+  // Create a new block to tag with a label and add a branch from


The labels as values gcc extension is not part of this patch, but I wonder how that will look like. Should cir.label be a value in general or do we need a new op for AddrLabelExprs`?

Re to meeting discussion: we can do it similar to https://mlir.llvm.org/docs/Dialects/LLVM/#llvmblockaddress-llvmblockaddressop

This approach looks good. In the goto solver, we currently erase the label instead of lowering it:

llvm::StringMap<Block *> labels; ... labels.try_emplace(lab.getLabel(), lab->getBlock()); lab.erase();

I think this should be a new op, similar to LLVM::BlockAddressOp, and lowered to that.
One thing I noticed is that if the classic codegen version also uses BlockAddress in codegen, using a by value approach might lead to codegen looking different. Not sure what you guys think.

https://godbolt.org/z/YnnMv3h4x
@andykaylor

blockaddress in LLVM IR is a constant, derived from llvm::Value, so this will end up looking roughly equivalent to the way that CIR introduces CIR_ConstantOp to handle literal integer values. The basic idea of having a CIR_BlockAddressOp that lowers to LLVM_BlockAddressOp seems very solid to me.

andykaylor

lgtm, just a couple of nits

andykaylor · 2025-08-11T19:44:34Z

clang/lib/CIR/CodeGen/CIRGenFunction.h

+  mlir::LogicalResult emitLabel(const clang::LabelDecl *d);
+  mlir::LogicalResult emitLabelStmt(const clang::LabelStmt &s);


It's true. These signatures follow the equivalents in OGCG, which is likewise inconsistent. (Not that that's a good excuse for propagating the inconsistency.)

andykaylor · 2025-08-11T19:52:14Z

clang/include/clang/CIR/Dialect/IR/CIROps.td

+// LabelOp
+//===----------------------------------------------------------------------===//
+
+// The LabelOp has AlwaysSpeculatable trait in order to not to be swept by canonicalizer


Can you reformat this for 80 columns?

andykaylor · 2025-08-11T19:55:46Z

clang/test/CIR/CodeGen/label.c

+// CIR:  cir.func no_proto dso_local @label
+// CIR:    cir.label "labelA"
+// CIR:    cir.return
+


I take it we aren't lowering to LLVM IR through CIR because that requires the GotoSolver. Can you add a comment here to that effect?

bcardosolopes · 2025-08-12T02:07:24Z

clang/lib/CIR/CodeGen/CIRGenFunction.h

+  mlir::LogicalResult emitLabel(const clang::LabelDecl *d);
+  mlir::LogicalResult emitLabelStmt(const clang::LabelStmt &s);


yea, probably worth picking just one for this PR.

bcardosolopes · 2025-08-12T02:09:15Z

clang/lib/CIR/CodeGen/CIRGenStmt.cpp

 }

+mlir::LogicalResult CIRGenFunction::emitLabel(const clang::LabelDecl *d) {
+  // Create a new block to tag with a label and add a branch from


Re to meeting discussion: we can do it similar to https://mlir.llvm.org/docs/Dialects/LLVM/#llvmblockaddress-llvmblockaddressop

bcardosolopes · 2025-08-12T02:10:25Z

clang/lib/CIR/Dialect/IR/CIRDialect.cpp

+  mlir::Operation *op = getOperation();
+  mlir::Block *blk = op->getBlock();
+  if (&blk->front() != op)
+    return emitError() << "must be the first operation in a block";


This verifier error needs also a test!

github-actions · 2025-08-12T19:50:53Z

✅ With the latest revision this PR passed the C/C++ code formatter.

[CIR] Upstream LabelOp

89404b5

Andres-Salamanca requested review from andykaylor, bcardosolopes, erichkeane, mmha and xlauko August 8, 2025 21:34

Andres-Salamanca requested a review from lanza as a code owner August 8, 2025 21:34

llvmbot added clang Clang issues not falling into any other category ClangIR Anything related to the ClangIR project labels Aug 8, 2025

mmha approved these changes Aug 11, 2025

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mmha mentioned this pull request Aug 11, 2025

[CIR] Introduce more cleanup infrastructure #152589

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andykaylor approved these changes Aug 11, 2025

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bcardosolopes reviewed Aug 12, 2025

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Andres-Salamanca requested a review from bcardosolopes August 12, 2025 19:49

Fix formatting

a290058

Andres-Salamanca merged commit 4b112d2 into llvm:main Aug 13, 2025
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Andres-Salamanca mentioned this pull request Aug 21, 2025

[CIR] Upstream support for goto handling #153288

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		mlir::LogicalResult emitLabel(const clang::LabelDecl *d);
		mlir::LogicalResult emitLabelStmt(const clang::LabelStmt &s);

[CIR] Upstream LabelOp #152802

[CIR] Upstream LabelOp #152802

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