Alex Richardson d1ff003fbb [SelectionDAGBuilder] Stop setting alignment to one for hidden sret values ...

We allocated a suitably aligned frame index so we know that all the values
have ABI alignment.
For MIPS this avoids using pair of lwl + lwr instructions instead of a
single lw. I found this when compiling CHERI pure capability code where
we can't use the lwl/lwr unaligned loads/stores and and were to falling
back to a byte load + shift + or sequence.

This should save a few instructions for MIPS and possibly other backends
that don't have fast unaligned loads/stores.
It also improves code generation for CodeGen/X86/pr34653.ll and
CodeGen/WebAssembly/offset.ll since they can now use aligned loads.

Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D78999

2020-05-04 14:44:39 +01:00

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