[CIR] Upstream support for range-based for loops (#138176)

This upstreams the code needed to handle CXXForRangeStmt.

Author: andykaylor

clang/lib/CIR/CodeGen/CIRGenExpr.cpp

@@ -948,6 +948,41 @@ void CIRGenFunction::emitIgnoredExpr(const Expr *e) {
   emitLValue(e);
 }
 
+Address CIRGenFunction::emitArrayToPointerDecay(const Expr *e) {
+  assert(e->getType()->isArrayType() &&
+         "Array to pointer decay must have array source type!");
+
+  // Expressions of array type can't be bitfields or vector elements.
+  LValue lv = emitLValue(e);
+  Address addr = lv.getAddress();
+
+  // If the array type was an incomplete type, we need to make sure
+  // the decay ends up being the right type.
+  auto lvalueAddrTy = mlir::cast<cir::PointerType>(addr.getPointer().getType());
+
+  if (e->getType()->isVariableArrayType())
+    return addr;
+
+  auto pointeeTy = mlir::cast<cir::ArrayType>(lvalueAddrTy.getPointee());
+
+  mlir::Type arrayTy = convertType(e->getType());
+  assert(mlir::isa<cir::ArrayType>(arrayTy) && "expected array");
+  assert(pointeeTy == arrayTy);
+
+  // The result of this decay conversion points to an array element within the
+  // base lvalue. However, since TBAA currently does not support representing
+  // accesses to elements of member arrays, we conservatively represent accesses
+  // to the pointee object as if it had no any base lvalue specified.
+  // TODO: Support TBAA for member arrays.
+  QualType eltType = e->getType()->castAsArrayTypeUnsafe()->getElementType();
+  assert(!cir::MissingFeatures::opTBAA());
+
+  mlir::Value ptr = builder.maybeBuildArrayDecay(
+      cgm.getLoc(e->getSourceRange()), addr.getPointer(),
+      convertTypeForMem(eltType));
+  return Address(ptr, addr.getAlignment());
+}
+
 /// Emit an `if` on a boolean condition, filling `then` and `else` into
 /// appropriated regions.
 mlir::LogicalResult CIRGenFunction::emitIfOnBoolExpr(const Expr *cond,

clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp

@@ -1567,6 +1567,9 @@ mlir::Value ScalarExprEmitter::VisitCastExpr(CastExpr *ce) {
     return v;
   }
 
+  case CK_ArrayToPointerDecay:
+    return cgf.emitArrayToPointerDecay(subExpr).getPointer();
+
   case CK_NullToPointer: {
     if (mustVisitNullValue(subExpr))
       cgf.emitIgnoredExpr(subExpr);

clang/lib/CIR/CodeGen/CIRGenFunction.h

@@ -449,6 +449,8 @@ class CIRGenFunction : public CIRGenTypeCache {
 
   LValue emitArraySubscriptExpr(const clang::ArraySubscriptExpr *e);
 
+  Address emitArrayToPointerDecay(const Expr *array);
+
   AutoVarEmission emitAutoVarAlloca(const clang::VarDecl &d);
 
   /// Emit code and set up symbol table for a variable declaration with auto,
@@ -485,6 +487,10 @@ class CIRGenFunction : public CIRGenTypeCache {
   LValue emitCompoundAssignmentLValue(const clang::CompoundAssignOperator *e);
 
   mlir::LogicalResult emitContinueStmt(const clang::ContinueStmt &s);
+
+  mlir::LogicalResult emitCXXForRangeStmt(const CXXForRangeStmt &s,
+                                          llvm::ArrayRef<const Attr *> attrs);
+
   mlir::LogicalResult emitDoStmt(const clang::DoStmt &s);
 
   /// Emit an expression as an initializer for an object (variable, field, etc.)

clang/lib/CIR/CodeGen/CIRGenStmt.cpp

@@ -97,6 +97,8 @@ mlir::LogicalResult CIRGenFunction::emitStmt(const Stmt *s,
     return emitWhileStmt(cast<WhileStmt>(*s));
   case Stmt::DoStmtClass:
     return emitDoStmt(cast<DoStmt>(*s));
+  case Stmt::CXXForRangeStmtClass:
+    return emitCXXForRangeStmt(cast<CXXForRangeStmt>(*s), attr);
   case Stmt::OpenACCComputeConstructClass:
     return emitOpenACCComputeConstruct(cast<OpenACCComputeConstruct>(*s));
   case Stmt::OpenACCLoopConstructClass:
@@ -137,7 +139,6 @@ mlir::LogicalResult CIRGenFunction::emitStmt(const Stmt *s,
   case Stmt::CoroutineBodyStmtClass:
   case Stmt::CoreturnStmtClass:
   case Stmt::CXXTryStmtClass:
-  case Stmt::CXXForRangeStmtClass:
   case Stmt::IndirectGotoStmtClass:
   case Stmt::GCCAsmStmtClass:
   case Stmt::MSAsmStmtClass:
@@ -547,6 +548,83 @@ mlir::LogicalResult CIRGenFunction::emitSwitchCase(const SwitchCase &s,
   llvm_unreachable("expect case or default stmt");
 }
 
+mlir::LogicalResult
+CIRGenFunction::emitCXXForRangeStmt(const CXXForRangeStmt &s,
+                                    ArrayRef<const Attr *> forAttrs) {
+  cir::ForOp forOp;
+
+  // TODO(cir): pass in array of attributes.
+  auto forStmtBuilder = [&]() -> mlir::LogicalResult {
+    mlir::LogicalResult loopRes = mlir::success();
+    // Evaluate the first pieces before the loop.
+    if (s.getInit())
+      if (emitStmt(s.getInit(), /*useCurrentScope=*/true).failed())
+        return mlir::failure();
+    if (emitStmt(s.getRangeStmt(), /*useCurrentScope=*/true).failed())
+      return mlir::failure();
+    if (emitStmt(s.getBeginStmt(), /*useCurrentScope=*/true).failed())
+      return mlir::failure();
+    if (emitStmt(s.getEndStmt(), /*useCurrentScope=*/true).failed())
+      return mlir::failure();
+
+    assert(!cir::MissingFeatures::loopInfoStack());
+    // From LLVM: if there are any cleanups between here and the loop-exit
+    // scope, create a block to stage a loop exit along.
+    // We probably already do the right thing because of ScopeOp, but make
+    // sure we handle all cases.
+    assert(!cir::MissingFeatures::requiresCleanups());
+
+    forOp = builder.createFor(
+        getLoc(s.getSourceRange()),
+        /*condBuilder=*/
+        [&](mlir::OpBuilder &b, mlir::Location loc) {
+          assert(!cir::MissingFeatures::createProfileWeightsForLoop());
+          assert(!cir::MissingFeatures::emitCondLikelihoodViaExpectIntrinsic());
+          mlir::Value condVal = evaluateExprAsBool(s.getCond());
+          builder.createCondition(condVal);
+        },
+        /*bodyBuilder=*/
+        [&](mlir::OpBuilder &b, mlir::Location loc) {
+          // https://en.cppreference.com/w/cpp/language/for
+          // In C++ the scope of the init-statement and the scope of
+          // statement are one and the same.
+          bool useCurrentScope = true;
+          if (emitStmt(s.getLoopVarStmt(), useCurrentScope).failed())
+            loopRes = mlir::failure();
+          if (emitStmt(s.getBody(), useCurrentScope).failed())
+            loopRes = mlir::failure();
+          emitStopPoint(&s);
+        },
+        /*stepBuilder=*/
+        [&](mlir::OpBuilder &b, mlir::Location loc) {
+          if (s.getInc())
+            if (emitStmt(s.getInc(), /*useCurrentScope=*/true).failed())
+              loopRes = mlir::failure();
+          builder.createYield(loc);
+        });
+    return loopRes;
+  };
+
+  mlir::LogicalResult res = mlir::success();
+  mlir::Location scopeLoc = getLoc(s.getSourceRange());
+  builder.create<cir::ScopeOp>(scopeLoc, /*scopeBuilder=*/
+                               [&](mlir::OpBuilder &b, mlir::Location loc) {
+                                 // Create a cleanup scope for the condition
+                                 // variable cleanups. Logical equivalent from
+                                 // LLVM codegn for LexicalScope
+                                 // ConditionScope(*this, S.getSourceRange())...
+                                 LexicalScope lexScope{
+                                     *this, loc, builder.getInsertionBlock()};
+                                 res = forStmtBuilder();
+                               });
+
+  if (res.failed())
+    return res;
+
+  terminateBody(builder, forOp.getBody(), getLoc(s.getEndLoc()));
+  return mlir::success();
+}
+
 mlir::LogicalResult CIRGenFunction::emitForStmt(const ForStmt &s) {
   cir::ForOp forOp;