[flang] add fir.declare codegen support

For now, nothing is done about debug info and the fir.declare is simply
replaced by the memref argument. This is done in the PreCGRewrite in
order to avoid requiring adding support for fir.shape codegen, which
would still be useless and undesired at that point.

Differential Revision: https://reviews.llvm.org/D136254

Author: jeanPerier

flang/lib/Optimizer/CodeGen/PreCGRewrite.cpp

@@ -266,6 +266,18 @@ class ArrayCoorConversion : public mlir::OpRewritePattern<fir::ArrayCoorOp> {
   }
 };
 
+class DeclareOpConversion : public mlir::OpRewritePattern<fir::DeclareOp> {
+public:
+  using OpRewritePattern::OpRewritePattern;
+
+  mlir::LogicalResult
+  matchAndRewrite(fir::DeclareOp declareOp,
+                  mlir::PatternRewriter &rewriter) const override {
+    rewriter.replaceOp(declareOp, declareOp.getMemref());
+    return mlir::success();
+  }
+};
+
 class CodeGenRewrite : public fir::impl::CodeGenRewriteBase<CodeGenRewrite> {
 public:
   void runOn(mlir::Operation *op, mlir::Region &region) {
@@ -276,15 +288,16 @@ class CodeGenRewrite : public fir::impl::CodeGenRewriteBase<CodeGenRewrite> {
                            fir::FIRCodeGenDialect, mlir::func::FuncDialect>();
     target.addIllegalOp<fir::ArrayCoorOp>();
     target.addIllegalOp<fir::ReboxOp>();
+    target.addIllegalOp<fir::DeclareOp>();
     target.addDynamicallyLegalOp<fir::EmboxOp>([](fir::EmboxOp embox) {
       return !(embox.getShape() || embox.getType()
                                        .cast<fir::BaseBoxType>()
                                        .getEleTy()
                                        .isa<fir::SequenceType>());
     });
     mlir::RewritePatternSet patterns(&context);
-    patterns.insert<EmboxConversion, ArrayCoorConversion, ReboxConversion>(
-        &context);
+    patterns.insert<EmboxConversion, ArrayCoorConversion, ReboxConversion,
+                    DeclareOpConversion>(&context);
     if (mlir::failed(
             mlir::applyPartialConversion(op, target, std::move(patterns)))) {
       mlir::emitError(mlir::UnknownLoc::get(&context),

flang/test/Fir/declare-codegen.fir

@@ -0,0 +1,20 @@
+// Test rewrite of fir.declare. The result is replaced by the memref operand.
+// RUN: fir-opt --cg-rewrite %s -o - | FileCheck %s
+
+
+func.func @test(%arg0: !fir.ref<!fir.array<12x23xi32>>) {
+  %c-1 = arith.constant -1 : index
+  %c12 = arith.constant 12 : index
+  %c-2 = arith.constant -2 : index
+  %c23 = arith.constant 23 : index
+  %0 = fir.shape_shift %c12, %c-1, %c23, %c-2 : (index, index, index, index) -> !fir.shapeshift<2>
+  %1 = fir.declare %arg0(%0) {uniq_name = "_QFarray_numeric_lboundsEx"} : (!fir.ref<!fir.array<12x23xi32>>, !fir.shapeshift<2>) -> !fir.ref<!fir.array<12x23xi32>>
+  fir.call @bar(%1) : (!fir.ref<!fir.array<12x23xi32>>) -> ()
+  return
+}
+func.func private @bar(%arg0: !fir.ref<!fir.array<12x23xi32>>)
+
+
+// CHECK-LABEL: func.func @test(
+// CHECK-SAME: %[[arg0:.*]]: !fir.ref<!fir.array<12x23xi32>>) {
+// CHECK-NEXT: fir.call @bar(%[[arg0]]) : (!fir.ref<!fir.array<12x23xi32>>) -> ()