[mlir][EmitC]Expand the MemRefToEmitC pass - Adding scalars (#148055)

This aims to expand the the MemRefToEmitC pass so that it can accept
global scalars.
From:
```
memref.global "private" constant @__constant_xi32 : memref<i32> = dense<-1>
func.func @globals() {
    memref.get_global @__constant_xi32 : memref<i32>
}
```
To:
```
emitc.global static const @__constant_xi32 : i32 = -1
    emitc.func @globals() {
      %0 = get_global @__constant_xi32 : !emitc.lvalue<i32>
      %1 = apply "&"(%0) : (!emitc.lvalue<i32>) -> !emitc.ptr<i32>
      return
    }
```

2 files changed, 38 insertions, 3 deletions

diff --git a/mlir/lib/Conversion/MemRefToEmitC/MemRefToEmitC.cpp b/mlir/lib/Conversion/MemRefToEmitC/MemRefToEmitC.cpp
index db244d1..0b7ffa4 100644
--- a/mlir/lib/Conversion/MemRefToEmitC/MemRefToEmitC.cpp
+++ b/mlir/lib/Conversion/MemRefToEmitC/MemRefToEmitC.cpp
@@ -16,7 +16,9 @@
 #include "mlir/Dialect/EmitC/IR/EmitC.h"
 #include "mlir/Dialect/MemRef/IR/MemRef.h"
 #include "mlir/IR/Builders.h"
+#include "mlir/IR/BuiltinTypes.h"
 #include "mlir/IR/PatternMatch.h"
+#include "mlir/IR/TypeRange.h"
 #include "mlir/Transforms/DialectConversion.h"
 
 using namespace mlir;
@@ -77,13 +79,23 @@ struct ConvertAlloca final : public OpConversionPattern<memref::AllocaOp> {
   }
 };
 
+Type convertMemRefType(MemRefType opTy, const TypeConverter *typeConverter) {
+  Type resultTy;
+  if (opTy.getRank() == 0) {
+    resultTy = typeConverter->convertType(mlir::getElementTypeOrSelf(opTy));
+  } else {
+    resultTy = typeConverter->convertType(opTy);
+  }
+  return resultTy;
+}
+
 struct ConvertGlobal final : public OpConversionPattern<memref::GlobalOp> {
   using OpConversionPattern::OpConversionPattern;
 
   LogicalResult
   matchAndRewrite(memref::GlobalOp op, OpAdaptor operands,
                   ConversionPatternRewriter &rewriter) const override {
-
+    MemRefType opTy = op.getType();
     if (!op.getType().hasStaticShape()) {
       return rewriter.notifyMatchFailure(
           op.getLoc(), "cannot transform global with dynamic shape");
@@ -95,7 +107,9 @@ struct ConvertGlobal final : public OpConversionPattern<memref::GlobalOp> {
           op.getLoc(), "global variable with alignment requirement is "
                        "currently not supported");
     }
-    auto resultTy = getTypeConverter()->convertType(op.getType());
+
+    Type resultTy = convertMemRefType(opTy, getTypeConverter());
+
     if (!resultTy) {
       return rewriter.notifyMatchFailure(op.getLoc(),
                                          "cannot convert result type");
@@ -114,6 +128,10 @@ struct ConvertGlobal final : public OpConversionPattern<memref::GlobalOp> {
     bool externSpecifier = !staticSpecifier;
 
     Attribute initialValue = operands.getInitialValueAttr();
+    if (opTy.getRank() == 0) {
+      auto elementsAttr = llvm::cast<ElementsAttr>(*op.getInitialValue());
+      initialValue = elementsAttr.getSplatValue<Attribute>();
+    }
     if (isa_and_present<UnitAttr>(initialValue))
       initialValue = {};
 
@@ -132,11 +150,23 @@ struct ConvertGetGlobal final
   matchAndRewrite(memref::GetGlobalOp op, OpAdaptor operands,
                   ConversionPatternRewriter &rewriter) const override {
 
-    auto resultTy = getTypeConverter()->convertType(op.getType());
+    MemRefType opTy = op.getType();
+    Type resultTy = convertMemRefType(opTy, getTypeConverter());
+
     if (!resultTy) {
       return rewriter.notifyMatchFailure(op.getLoc(),
                                          "cannot convert result type");
     }
+
+    if (opTy.getRank() == 0) {
+      emitc::LValueType lvalueType = emitc::LValueType::get(resultTy);
+      emitc::GetGlobalOp globalLValue = rewriter.create<emitc::GetGlobalOp>(
+          op.getLoc(), lvalueType, operands.getNameAttr());
+      emitc::PointerType pointerType = emitc::PointerType::get(resultTy);
+      rewriter.replaceOpWithNewOp<emitc::ApplyOp>(
+          op, pointerType, rewriter.getStringAttr("&"), globalLValue);
+      return success();
+    }
     rewriter.replaceOpWithNewOp<emitc::GetGlobalOp>(op, resultTy,
                                                     operands.getNameAttr());
     return success();
diff --git a/mlir/test/Conversion/MemRefToEmitC/memref-to-emitc.mlir b/mlir/test/Conversion/MemRefToEmitC/memref-to-emitc.mlir
index d37fd1d..2b4eda3 100644
--- a/mlir/test/Conversion/MemRefToEmitC/memref-to-emitc.mlir
+++ b/mlir/test/Conversion/MemRefToEmitC/memref-to-emitc.mlir
@@ -41,6 +41,8 @@ func.func @memref_load(%buff : memref<4x8xf32>, %i: index, %j: index) -> f32 {
 module @globals {
   memref.global "private" constant @internal_global : memref<3x7xf32> = dense<4.0>
   // CHECK-NEXT: emitc.global static const @internal_global : !emitc.array<3x7xf32> = dense<4.000000e+00>
+  memref.global "private" constant @__constant_xi32 : memref<i32> = dense<-1>
+  // CHECK-NEXT: emitc.global static const @__constant_xi32 : i32 = -1
   memref.global @public_global : memref<3x7xf32>
   // CHECK-NEXT: emitc.global extern @public_global : !emitc.array<3x7xf32>
   memref.global @uninitialized_global : memref<3x7xf32> = uninitialized
@@ -50,6 +52,9 @@ module @globals {
   func.func @use_global() {
     // CHECK-NEXT: emitc.get_global @public_global : !emitc.array<3x7xf32>
     %0 = memref.get_global @public_global : memref<3x7xf32>
+    // CHECK-NEXT: emitc.get_global @__constant_xi32 : !emitc.lvalue<i32>
+    // CHECK-NEXT: emitc.apply "&"(%1) : (!emitc.lvalue<i32>) -> !emitc.ptr<i32>
+    %1 = memref.get_global @__constant_xi32 : memref<i32>
     return
   }
 }