[clang] [CIR] Upstream lowering of conditional operators to TernaryOp (PR #138156)

[Andy Kaylor via cfe-commits]

================
@@ -948,6 +950,165 @@ void CIRGenFunction::emitIgnoredExpr(const Expr *e) {
   emitLValue(e);
 }
 
+// Handle the case where the condition is a constant evaluatable simple integer,
+// which means we don't have to separately handle the true/false blocks.
+static std::optional<LValue> handleConditionalOperatorLValueSimpleCase(
+    CIRGenFunction &cgf, const AbstractConditionalOperator *e) {
+  const Expr *condExpr = e->getCond();
+  bool condExprBool = false;
+  if (cgf.constantFoldsToSimpleInteger(condExpr, condExprBool)) {
+    const Expr *live = e->getTrueExpr(), *dead = e->getFalseExpr();
+    if (!condExprBool)
+      std::swap(live, dead);
+
+    if (!cgf.containsLabel(dead)) {
+      // If the true case is live, we need to track its region.
+      if (condExprBool) {
+        assert(!cir::MissingFeatures::incrementProfileCounter());
+      }
+      // If a throw expression we emit it and return an undefined lvalue
+      // because it can't be used.
+      if (isa<CXXThrowExpr>(live->IgnoreParens())) {
+        assert(!cir::MissingFeatures::throwOp());
+        cgf.cgm.errorNYI(live->getSourceRange(),
+                         "throw expressions in conditional operator");
+        return std::nullopt;
+      }
+      return cgf.emitLValue(live);
+    }
+  }
+  return std::nullopt;
+}
+
+/// Emit the operand of a glvalue conditional operator. This is either a glvalue
+/// or a (possibly-parenthesized) throw-expression. If this is a throw, no
+/// LValue is returned and the current block has been terminated.
+static std::optional<LValue> emitLValueOrThrowExpression(CIRGenFunction &cgf,
+                                                         const Expr *operand) {
+  if (isa<CXXThrowExpr>(operand->IgnoreParens())) {
+    assert(!cir::MissingFeatures::throwOp());
+    cgf.cgm.errorNYI(operand->getSourceRange(),
+                     "throw expressions in conditional operator");
+    return std::nullopt;
+  }
+
+  return cgf.emitLValue(operand);
+}
+
+// Create and generate the 3 blocks for a conditional operator.
+// Leaves the 'current block' in the continuation basic block.
+template <typename FuncTy>
+CIRGenFunction::ConditionalInfo
+CIRGenFunction::emitConditionalBlocks(const AbstractConditionalOperator *e,
+                                      const FuncTy &branchGenFunc) {
+  ConditionalInfo info;
+  CIRGenFunction &cgf = *this;
+  ConditionalEvaluation eval(cgf);
+  mlir::Location loc = cgf.getLoc(e->getSourceRange());
+  CIRGenBuilderTy &builder = cgf.getBuilder();
+  Expr *trueExpr = e->getTrueExpr();
+  Expr *falseExpr = e->getFalseExpr();
+
+  mlir::Value condV = cgf.emitOpOnBoolExpr(loc, e->getCond());
+  SmallVector<mlir::OpBuilder::InsertPoint, 2> insertPoints{};
+  mlir::Type yieldTy{};
+
+  auto emitBranch = [&](mlir::OpBuilder &b, mlir::Location loc, Expr *expr,
+                        std::optional<LValue> &branchInfo) {
+    CIRGenFunction::LexicalScope lexScope{cgf, loc, b.getInsertionBlock()};
+    cgf.curLexScope->setAsTernary();
+
+    assert(!cir::MissingFeatures::incrementProfileCounter());
+    eval.begin(cgf);
+    branchInfo = branchGenFunc(cgf, expr);
+    mlir::Value branch = branchInfo->getPointer();
+    eval.end(cgf);
+
+    if (branch) {
+      yieldTy = branch.getType();
+      b.create<cir::YieldOp>(loc, branch);
+    } else {
+      // If LHS or RHS is a throw or void expression we need to patch
+      // arms as to properly match yield types.
+      insertPoints.push_back(b.saveInsertionPoint());
+    }
+  };
+
+  info.result = builder
+                    .create<cir::TernaryOp>(
+                        loc, condV, /*trueBuilder=*/
+                        [&](mlir::OpBuilder &b, mlir::Location loc) {
+                          emitBranch(b, loc, trueExpr, info.lhs);
+                        },
+                        /*falseBuilder=*/
+                        [&](mlir::OpBuilder &b, mlir::Location loc) {
+                          emitBranch(b, loc, falseExpr, info.rhs);
+                        })
+                    .getResult();
+
+  if (!insertPoints.empty()) {
+    // If both arms are void, so be it.
+    if (!yieldTy)
+      yieldTy = cgf.VoidTy;
+
+    // Insert required yields.
+    for (mlir::OpBuilder::InsertPoint &toInsert : insertPoints) {
+      mlir::OpBuilder::InsertionGuard guard(builder);
+      builder.restoreInsertionPoint(toInsert);
+
+      // Block does not return: build empty yield.
+      if (mlir::isa<cir::VoidType>(yieldTy)) {
+        builder.create<cir::YieldOp>(loc);
+      } else { // Block returns: set null yield value.
+        mlir::Value op0 = builder.getNullValue(yieldTy, loc);
----------------
andykaylor wrote:

I don't think this is right. If a block contains a throw, the incubator generates a `cir.throw` followed by a `cir.unreachable` and then inserts a null constant and a `cir.yield`. This causes verification to fail because `cir.unreachable` isn't the last operation in the block.

https://github.com/llvm/llvm-project/pull/138156