[CIR][CIRGen] Use #cir.zero on zero-initialized global arrays

ghstack-source-id: 1f793b2
Pull Request resolved: llvm#207

Author: sitio-couto

clang/lib/CIR/CodeGen/CIRGenBuilder.h

@@ -174,16 +174,8 @@ class CIRGenBuilderTy : public mlir::OpBuilder {
       return mlir::cir::IntAttr::get(ty, 0);
     if (ty.isa<mlir::FloatType>())
       return mlir::FloatAttr::get(ty, 0.0);
-    if (auto arrTy = ty.dyn_cast<mlir::cir::ArrayType>()) {
-      // FIXME(cir): We should have a proper zero initializer CIR instead of
-      // manually pumping zeros into the array.
-      assert(!UnimplementedFeature::zeroInitializer());
-      auto values = llvm::SmallVector<mlir::Attribute, 4>();
-      auto zero = getZeroInitAttr(arrTy.getEltType());
-      for (unsigned i = 0, e = arrTy.getSize(); i < e; ++i)
-        values.push_back(zero);
-      return getConstArray(mlir::ArrayAttr::get(getContext(), values), arrTy);
-    }
+    if (auto arrTy = ty.dyn_cast<mlir::cir::ArrayType>())
+      return getZeroAttr(arrTy);
     if (auto ptrTy = ty.dyn_cast<mlir::cir::PointerType>())
       return getNullPtrAttr(ptrTy);
     if (auto structTy = ty.dyn_cast<mlir::cir::StructType>())

clang/lib/CIR/CodeGen/CIRGenExprConst.cpp

@@ -957,7 +957,7 @@ buildArrayConstant(CIRGenModule &CGM, mlir::Type DesiredType,
   }
 
   if (NonzeroLength == 0)
-    assert(0 && "NYE");
+    return builder.getZeroInitAttr(DesiredType);
 
   // Add a zeroinitializer array filler if we have lots of trailing zeroes.
   unsigned TrailingZeroes = ArrayBound - NonzeroLength;

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

@@ -170,10 +170,9 @@ static LogicalResult checkConstantTypes(mlir::Operation *op, mlir::Type opType,
   }
 
   if (attrType.isa<ZeroAttr>()) {
-    // FIXME: should also support arrays / const_arrays.
-    if (opType.isa<::mlir::cir::StructType>())
+    if (opType.isa<::mlir::cir::StructType, ::mlir::cir::ArrayType>())
       return success();
-    return op->emitOpError("zero expects struct type");
+    return op->emitOpError("zero expects struct or array type");
   }
 
   if (attrType.isa<mlir::cir::BoolAttr>()) {

clang/test/CIR/CodeGen/array.cpp

@@ -61,3 +61,7 @@ int multidim(int i, int j) {
 // CHECK: %7 = cir.load %{{.+}} : cir.ptr <!s32i>, !s32i
 // CHECK: %8 = cir.cast(array_to_ptrdecay, %6 : !cir.ptr<!cir.array<!s32i x 2>>), !cir.ptr<!s32i>
 // CHECK: %9 = cir.ptr_stride(%8 : !cir.ptr<!s32i>, %7 : !s32i), !cir.ptr<!s32i>
+
+// Should globally zero-initialize null arrays.
+int globalNullArr[] = {0, 0};
+// CHECK: cir.global external @globalNullArr = #cir.zero : !cir.array<!s32i x 2>

clang/test/CIR/CodeGen/globals.c

@@ -36,5 +36,5 @@ int tentativeD[];
 float zeroInitFlt[2];
 // CHECK: cir.global external @tentativeA = #cir.int<0> : !s32i
 // CHECK: cir.global external @tentativeC = 0.000000e+00 : f32
-// CHECK: cir.global external @tentativeD = #cir.const_array<[#cir.int<0> : !s32i]> : !cir.array<!s32i x 1>
-// CHECK: cir.global external @zeroInitFlt = #cir.const_array<[0.000000e+00 : f32, 0.000000e+00 : f32]> : !cir.array<f32 x 2>
+// CHECK: cir.global external @tentativeD = #cir.zero : !cir.array<!s32i x 1>
+// CHECK: cir.global external @zeroInitFlt = #cir.zero : !cir.array<f32 x 2>

clang/test/CIR/IR/invalid.cir

@@ -259,7 +259,7 @@ cir.func @unary1() {
 
 !u32i = !cir.int<u, 32>
 module {
-  cir.global external @v = #cir.zero : !u32i // expected-error {{zero expects struct type}}
+  cir.global external @v = #cir.zero : !u32i // expected-error {{zero expects struct or array type}}
 }
 
 // -----