[flang] Inline hlfir.dot_product. (#123143)

Some good results for induct2, where dot_product is applied
to a vector of unknow size and a known 3-element vector:
the inlining ends up generating a 3-iteration loop, which
is then fully unrolled. With late FIR simplification
it is not happening even when the simplified intrinsics
implementation is inlined by LLVM (because the loop bounds
are not known).

This change just follows the current approach to expose
the loops for later worksharing application.

Author: vzakhari

flang/include/flang/Optimizer/Builder/HLFIRTools.h

@@ -513,6 +513,12 @@ genTypeAndKindConvert(mlir::Location loc, fir::FirOpBuilder &builder,
 Entity loadElementAt(mlir::Location loc, fir::FirOpBuilder &builder,
                      Entity entity, mlir::ValueRange oneBasedIndices);
 
+/// Return a vector of extents for the given entity.
+/// The function creates new operations, but tries to clean-up
+/// after itself.
+llvm::SmallVector<mlir::Value>
+genExtentsVector(mlir::Location loc, fir::FirOpBuilder &builder, Entity entity);
+
 } // namespace hlfir
 
 #endif // FORTRAN_OPTIMIZER_BUILDER_HLFIRTOOLS_H

flang/lib/Optimizer/Builder/HLFIRTools.cpp

@@ -1421,3 +1421,15 @@ hlfir::Entity hlfir::loadElementAt(mlir::Location loc,
   return loadTrivialScalar(loc, builder,
                            getElementAt(loc, builder, entity, oneBasedIndices));
 }
+
+llvm::SmallVector<mlir::Value>
+hlfir::genExtentsVector(mlir::Location loc, fir::FirOpBuilder &builder,
+                        hlfir::Entity entity) {
+  entity = hlfir::derefPointersAndAllocatables(loc, builder, entity);
+  mlir::Value shape = hlfir::genShape(loc, builder, entity);
+  llvm::SmallVector<mlir::Value, Fortran::common::maxRank> extents =
+      hlfir::getExplicitExtentsFromShape(shape, builder);
+  if (shape.getUses().empty())
+    shape.getDefiningOp()->erase();
+  return extents;
+}