Hal Finkel 21c68fac74 [PowerPC] Fix address-offset folding for plain addi
When folding an addi into a memory access that can take an immediate offset, we
were implicitly assuming that the existing offset was zero. This was incorrect.
If we're dealing with an addi with a plain constant, we can add it to the
existing offset (assuming that doesn't overflow the immediate, etc.), but if we
have anything else (i.e. something that will become a relocation expression),
we'll go back to requiring the existing immediate offset to be zero (because we
don't know what the requirements on that relocation expression might be - e.g.
maybe it is paired with some addis in some relevant way).

On the other hand, when dealing with a plain addi with a regular constant
immediate, the alignment restrictions (from the TOC base pointer, etc.) are
irrelevant.

I've added the test case from PR30280, which demonstrated the bug, but also
demonstrates a missed optimization opportunity (i.e. we don't need the memory
accesses at all).

Fixes PR30280.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280789 91177308-0d34-0410-b5e6-96231b3b80d8
2016-09-07 07:36:11 +00:00
..
2016-09-06 19:16:48 +00:00