[Hexagon] Add Hexagon Load Widening Pass (llvm#116330)

Extend existing store widening pass to widen load instructions.

This patch also borrows the alias check algorithm from AMDGPU's load
store widening pass.

Widened load instruction is inserted before the first candidate load
instruction.
Widened store instruction is inserted after the last candidate store
instruction.
This method helps avoid moving uses/defs when replacing load/store
instructions with their widened equivalents.

The pass has also been extended to
* Generate 64-bit widened stores
* Handle 32-bit post increment load/store
* Handle stores of non-immediate values
* Handle stores where the offset is a GlobalValue

Author: yandalur

llvm/lib/Target/Hexagon/CMakeLists.txt

@@ -59,7 +59,7 @@ add_llvm_target(HexagonCodeGen
   HexagonSelectionDAGInfo.cpp
   HexagonSplitConst32AndConst64.cpp
   HexagonSplitDouble.cpp
-  HexagonStoreWidening.cpp
+  HexagonLoadStoreWidening.cpp
   HexagonSubtarget.cpp
   HexagonTargetMachine.cpp
   HexagonTargetObjectFile.cpp