[CIR][Lowering] Fixed break/continue lowering for loops (llvm#211)

This PR fixes lowering for `break/continue`  in loops.
The idea is to replace `cir.yield break` and `cir.yield continue` with
the branch operations to the corresponding blocks. Note, that we need to
ignore nesting loops and don't touch `break` in switch operations. Also,
`yield` from `if` need to be considered only when it's not the loop
`yield` and `continue` in switch is ignored since it's processed in the
loops lowering.

Fixes llvm#160

Author: gitoleg

clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp

@@ -240,6 +240,47 @@ class CIRLoopOpLowering : public mlir::OpConversionPattern<mlir::cir::LoopOp> {
     return mlir::success();
   }
 
+  void makeYieldIf(mlir::cir::YieldOpKind kind, mlir::cir::YieldOp &op,
+                   mlir::Block *to,
+                   mlir::ConversionPatternRewriter &rewriter) const {
+    if (op.getKind() == kind) {
+      rewriter.setInsertionPoint(op);
+      rewriter.replaceOpWithNewOp<mlir::cir::BrOp>(op, op.getArgs(), to);
+    }
+  }
+
+  void
+  lowerNestedBreakContinue(mlir::Region &loopBody, mlir::Block *exitBlock,
+                           mlir::Block *continueBlock,
+                           mlir::ConversionPatternRewriter &rewriter) const {
+
+    auto processBreak = [&](mlir::Operation *op) {
+      if (isa<mlir::cir::LoopOp, mlir::cir::SwitchOp>(
+              *op)) // don't process breaks in nested loops and switches
+        return mlir::WalkResult::skip();
+
+      if (auto yield = dyn_cast<mlir::cir::YieldOp>(*op))
+        makeYieldIf(mlir::cir::YieldOpKind::Break, yield, exitBlock, rewriter);
+
+      return mlir::WalkResult::advance();
+    };
+
+    auto processContinue = [&](mlir::Operation *op) {
+      if (isa<mlir::cir::LoopOp>(
+              *op)) // don't process continues in nested loops
+        return mlir::WalkResult::skip();
+
+      if (auto yield = dyn_cast<mlir::cir::YieldOp>(*op))
+        makeYieldIf(mlir::cir::YieldOpKind::Continue, yield, continueBlock,
+                    rewriter);
+
+      return mlir::WalkResult::advance();
+    };
+
+    loopBody.walk<mlir::WalkOrder::PreOrder>(processBreak);
+    loopBody.walk<mlir::WalkOrder::PreOrder>(processContinue);
+  }
+
   mlir::LogicalResult
   matchAndRewrite(mlir::cir::LoopOp loopOp, OpAdaptor adaptor,
                   mlir::ConversionPatternRewriter &rewriter) const override {
@@ -267,6 +308,9 @@ class CIRLoopOpLowering : public mlir::OpConversionPattern<mlir::cir::LoopOp> {
     auto &stepFrontBlock = stepRegion.front();
     auto stepYield =
         dyn_cast<mlir::cir::YieldOp>(stepRegion.back().getTerminator());
+    auto &stepBlock = (kind == LoopKind::For ? stepFrontBlock : condFrontBlock);
+
+    lowerNestedBreakContinue(bodyRegion, continueBlock, &stepBlock, rewriter);
 
     // Move loop op region contents to current CFG.
     rewriter.inlineRegionBefore(condRegion, continueBlock);
@@ -289,8 +333,7 @@ class CIRLoopOpLowering : public mlir::OpConversionPattern<mlir::cir::LoopOp> {
 
     // Branch from body to condition or to step on for-loop cases.
     rewriter.setInsertionPoint(bodyYield);
-    auto &bodyExit = (kind == LoopKind::For ? stepFrontBlock : condFrontBlock);
-    rewriter.replaceOpWithNewOp<mlir::cir::BrOp>(bodyYield, &bodyExit);
+    rewriter.replaceOpWithNewOp<mlir::cir::BrOp>(bodyYield, &stepBlock);
 
     // Is a for loop: branch from step to condition.
     if (kind == LoopKind::For) {
@@ -488,6 +531,11 @@ class CIRCastOpLowering : public mlir::OpConversionPattern<mlir::cir::CastOp> {
   }
 };
 
+static bool isLoopYield(mlir::cir::YieldOp &op) {
+  return op.getKind() == mlir::cir::YieldOpKind::Break ||
+         op.getKind() == mlir::cir::YieldOpKind::Continue;
+}
+
 class CIRIfLowering : public mlir::OpConversionPattern<mlir::cir::IfOp> {
 public:
   using mlir::OpConversionPattern<mlir::cir::IfOp>::OpConversionPattern;
@@ -516,8 +564,10 @@ class CIRIfLowering : public mlir::OpConversionPattern<mlir::cir::IfOp> {
     rewriter.setInsertionPointToEnd(thenAfterBody);
     if (auto thenYieldOp =
             dyn_cast<mlir::cir::YieldOp>(thenAfterBody->getTerminator())) {
-      rewriter.replaceOpWithNewOp<mlir::cir::BrOp>(
-          thenYieldOp, thenYieldOp.getArgs(), continueBlock);
+      if (!isLoopYield(thenYieldOp)) // lowering of parent loop yields is
+                                     // deferred to loop lowering
+        rewriter.replaceOpWithNewOp<mlir::cir::BrOp>(
+            thenYieldOp, thenYieldOp.getArgs(), continueBlock);
     } else if (!dyn_cast<mlir::cir::ReturnOp>(thenAfterBody->getTerminator())) {
       llvm_unreachable("what are we terminating with?");
     }
@@ -545,8 +595,10 @@ class CIRIfLowering : public mlir::OpConversionPattern<mlir::cir::IfOp> {
       rewriter.setInsertionPointToEnd(elseAfterBody);
       if (auto elseYieldOp =
               dyn_cast<mlir::cir::YieldOp>(elseAfterBody->getTerminator())) {
-        rewriter.replaceOpWithNewOp<mlir::cir::BrOp>(
-            elseYieldOp, elseYieldOp.getArgs(), continueBlock);
+        if (!isLoopYield(elseYieldOp)) // lowering of parent loop yields is
+                                       // deferred to loop lowering
+          rewriter.replaceOpWithNewOp<mlir::cir::BrOp>(
+              elseYieldOp, elseYieldOp.getArgs(), continueBlock);
       } else if (!dyn_cast<mlir::cir::ReturnOp>(
                      elseAfterBody->getTerminator())) {
         llvm_unreachable("what are we terminating with?");
@@ -1109,6 +1161,9 @@ class CIRSwitchOpLowering
         case mlir::cir::YieldOpKind::Break:
           rewriteYieldOp(rewriter, yieldOp, exitBlock);
           break;
+        case mlir::cir::YieldOpKind::Continue: // Continue is handled only in
+                                               // loop lowering
+          break;
         default:
           return op->emitError("invalid yield kind in case statement");
         }
@@ -1692,8 +1747,7 @@ void populateCIRToLLVMConversionPatterns(mlir::RewritePatternSet &patterns,
                CIRVAStartLowering, CIRVAEndLowering, CIRVACopyLowering,
                CIRVAArgLowering, CIRBrOpLowering, CIRTernaryOpLowering,
                CIRStructElementAddrOpLowering, CIRSwitchOpLowering,
-               CIRPtrDiffOpLowering>(
-      converter, patterns.getContext());
+               CIRPtrDiffOpLowering>(converter, patterns.getContext());
 }
 
 namespace {