Commit Graph

8 Commits

Author SHA1 Message Date
Chandler Carruth 4b611a896d [x86] Teach the backend to fold more read-modify-write memory operands
to instructions.

These can't be reasonably matched in tablegen due to the handling of
flags, so we have to do this in C++ code. We only did it for `inc` and
`dec` historically, this starts fleshing that out to more interesting
instructions. Notably, this handles transfering operands to `add` and
`sub`.

Currently this forces them into a register. The next patch will add
support for keeping immediate operands as immediates. Then I'll extend
this beyond just `add` and `sub`.

I'm not super thrilled by the repeated switches in the code but
everything else I tried was really ugly or problematic.

Many thanks to Craig Topper for the suggestions about where to even
begin here and how to make this stuff work.

Differential Revision: https://reviews.llvm.org/D37130

llvm-svn: 311806
2017-08-25 22:50:52 +00:00
Amaury Sechet 2127452ff7 [DAGCombine] Make sure we check the ResNo from UADDO before combining
Summary: UADDO has 2 result, and one must check the result no before doing any kind of combine. Without it, the transform is invalid.

Reviewers: joerg

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D34088

llvm-svn: 305162
2017-06-11 11:36:38 +00:00
Amaury Sechet 9c5d1e966b [DAGCombine] Refactor common addcarry pattern.
Summary: This pattern is no very useful per se, but it exposes optimization for toehr patterns that wouldn't kick in otherwize. It's very common and worth optimizing for.

Reviewers: jyknight, nemanjai, mkuper, spatel, RKSimon, zvi, bkramer

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32756

llvm-svn: 304402
2017-06-01 10:48:04 +00:00
Amaury Sechet 2e43cb6d03 [DAGCombine] (add/uaddo X, Carry) -> (addcarry X, 0, Carry)
Summary:
This enables further transforms.

Depends on D32916

Reviewers: jyknight, nemanjai, mkuper, spatel, RKSimon, zvi, bkramer

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32925

llvm-svn: 304401
2017-06-01 10:42:39 +00:00
Amaury Sechet 77cfb4a85f [DAGCombine] (addcarry 0, 0, X) -> (ext/trunc X)
Summary:
While this makes some case better and some case worse - so it's unclear if it is a worthy combine just by itself - this is a useful canonicalisation.

As per discussion in D32756 .

Reviewers: jyknight, nemanjai, mkuper, spatel, RKSimon, zvi, bkramer

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32916

llvm-svn: 303441
2017-05-19 18:20:44 +00:00
Amaury Sechet 841b0907c4 Add more variations of addcarry in the tests. NFC.
llvm-svn: 302252
2017-05-05 16:27:55 +00:00
Amaury Sechet 666c705953 [DAGCombine] (addcarry (add|uaddo X, Y), 0, Carry) -> (addcarry X, Y, Carry)
Summary: Do the transform when the carry isn't used. It's a pattern exposed when legalizing large integers.

Reviewers: jyknight, nemanjai, mkuper, spatel, RKSimon, zvi, bkramer

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32755

llvm-svn: 302047
2017-05-03 16:28:10 +00:00
Amaury Sechet 3847996d74 Add new test case for addcarry. NFC.
llvm-svn: 301932
2017-05-02 16:07:32 +00:00