[DAGCombine] Fix alignment for offset loads/stores
The alignment parameter to getExtLoad is treated as a base alignment,
not the alignment of the load (base + offset). When we infer a better
alignment for a Ptr we need to ensure that it applies to the base to
prevent the alignment on the load from being wrong.
This fixes a bug where the alignment could then be used to incorrectly
prove noalias between a load and a store, leading to a miscompile.
Differential Revision: https://reviews.llvm.org/D48029
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@335210 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed
