[flang][NFC] Unify getIfConstantIntValue helpers (#87633)

There were different helpers for attempting to fetch compile time
constants from MLIR: one in fir::getIntIfConstant and one in CodeGen.
Unify the two.

Author: tblah

flang/include/flang/Optimizer/Dialect/FIROpsSupport.h

@@ -155,13 +155,7 @@ bool valueMayHaveFirAttributes(mlir::Value value,
 bool anyFuncArgsHaveAttr(mlir::func::FuncOp func, llvm::StringRef attr);
 
 /// Unwrap integer constant from an mlir::Value.
-inline std::optional<std::int64_t> getIntIfConstant(mlir::Value value) {
-  if (auto *definingOp = value.getDefiningOp())
-    if (auto cst = mlir::dyn_cast<mlir::arith::ConstantOp>(definingOp))
-      if (auto intAttr = cst.getValue().dyn_cast<mlir::IntegerAttr>())
-        return intAttr.getInt();
-  return {};
-}
+std::optional<std::int64_t> getIntIfConstant(mlir::Value value);
 
 static constexpr llvm::StringRef getAdaptToByRefAttrName() {
   return "adapt.valuebyref";

flang/lib/Optimizer/CodeGen/CodeGen.cpp

@@ -92,27 +92,10 @@ static mlir::Block *createBlock(mlir::ConversionPatternRewriter &rewriter,
                               mlir::Region::iterator(insertBefore));
 }
 
-/// Extract constant from a value if it is a result of one of the
-/// ConstantOp operations, otherwise, return std::nullopt.
-static std::optional<int64_t> getIfConstantIntValue(mlir::Value val) {
-  if (!val || !val.dyn_cast<mlir::OpResult>())
-    return {};
-
-  mlir::Operation *defop = val.getDefiningOp();
-
-  if (auto constOp = mlir::dyn_cast<mlir::arith::ConstantIntOp>(defop))
-    return constOp.value();
-  if (auto llConstOp = mlir::dyn_cast<mlir::LLVM::ConstantOp>(defop))
-    if (auto attr = llConstOp.getValue().dyn_cast<mlir::IntegerAttr>())
-      return attr.getValue().getSExtValue();
-
-  return {};
-}
-
 /// Extract constant from a value that must be the result of one of the
 /// ConstantOp operations.
 static int64_t getConstantIntValue(mlir::Value val) {
-  if (auto constVal = getIfConstantIntValue(val))
+  if (auto constVal = fir::getIntIfConstant(val))
     return *constVal;
   fir::emitFatalError(val.getLoc(), "must be a constant");
 }
@@ -664,7 +647,7 @@ struct ConvertOpConversion : public fir::FIROpConversion<fir::ConvertOp> {
                << " -> " << toTy;
 
       // Do folding for constant inputs.
-      if (auto constVal = getIfConstantIntValue(op0)) {
+      if (auto constVal = fir::getIntIfConstant(op0)) {
         mlir::Value normVal =
             genConstantIndex(loc, toTy, rewriter, *constVal ? 1 : 0);
         rewriter.replaceOp(convert, normVal);

flang/lib/Optimizer/Dialect/FIROps.cpp

@@ -3834,6 +3834,18 @@ bool fir::anyFuncArgsHaveAttr(mlir::func::FuncOp func, llvm::StringRef attr) {
   return false;
 }
 
+std::optional<std::int64_t> fir::getIntIfConstant(mlir::Value value) {
+  if (auto *definingOp = value.getDefiningOp()) {
+    if (auto cst = mlir::dyn_cast<mlir::arith::ConstantOp>(definingOp))
+      if (auto intAttr = cst.getValue().dyn_cast<mlir::IntegerAttr>())
+        return intAttr.getInt();
+    if (auto llConstOp = mlir::dyn_cast<mlir::LLVM::ConstantOp>(definingOp))
+      if (auto attr = llConstOp.getValue().dyn_cast<mlir::IntegerAttr>())
+        return attr.getValue().getSExtValue();
+  }
+  return {};
+}
+
 mlir::Type fir::applyPathToType(mlir::Type eleTy, mlir::ValueRange path) {
   for (auto i = path.begin(), end = path.end(); eleTy && i < end;) {
     eleTy = llvm::TypeSwitch<mlir::Type, mlir::Type>(eleTy)