[PATCH] Keep TBAA info when rewriting load and store DAG nodes

[Richard Sandiford]

Most SelectionDAG code drops the TBAA info when creating a new form of a load and store (e.g. during legalisation, or when converting a plain load to an extending one).  This patch tries to catch all cases where the TBAA information can legitimately be carried over.

There is nice getTruncStore() function that allows the original MachineMemOperand to be passed instead of the individual fields.  The patch adds a similar thing for getLoad() and getExtLoad().

The idea is to use the MachineMemOperand forms when all fields are carried over (size, pointer info, isVolatile, isNonTemporal, alignment and TBAA info).  If some adjustment is being made, e.g. to narrow the load, then we still pass the individual fields but also pass the TBAA info.

This is trying to update all uses in SelectionDAG/, so I don't have a testcase for all of them.  But the patch includes an example where the change helps for SystemZ.  (I'm hoping to make useAA() the default for SystemZ if this goes in, but that's a separate change.  I'll drop the explicit -combiner-* flags when that happens.)


http://llvm-reviews.chandlerc.com/D1894

Files:
  include/llvm/CodeGen/SelectionDAG.h
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
  lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp
  lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
  lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp
  lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
  lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp
  lib/CodeGen/SelectionDAG/SelectionDAG.cpp
  test/CodeGen/SystemZ/alias-01.ll
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