llvm-project

Commit Graph

Author	SHA1	Message	Date
David Green	e6f313b380	[Codegen] Alter the default promotion for saturating adds and subs The default promotion for the add_sat/sub_sat nodes currently does: ANY_EXTEND iN to iM SHL by M-N [US][ADD\|SUB]SAT L/ASHR by M-N If the promoted add_sat or sub_sat node is not legal, this can produce code that effectively does a lot of shifting (and requiring large constants to be materialised) just to use the overflow flag. It is simpler to just do the saturation manually, using the higher bitwidth addition and a min/max against the saturating bounds. That is what this patch attempts to do. Differential Revision: https://reviews.llvm.org/D68926 llvm-svn: 375211	2019-10-18 09:47:48 +00:00
David Green	fe2d15b39b	[Codegen] Adjust saturation test. NFC. Add some extra sat tests and adjust some of the existing tests to use signext where it would naturally be. llvm-svn: 375009	2019-10-16 15:50:42 +00:00

Author

SHA1

Message

Date

David Green

e6f313b380

[Codegen] Alter the default promotion for saturating adds and subs

The default promotion for the add_sat/sub_sat nodes currently does:
    ANY_EXTEND iN to iM
    SHL by M-N
    [US][ADD|SUB]SAT
    L/ASHR by M-N

If the promoted add_sat or sub_sat node is not legal, this can produce code
that effectively does a lot of shifting (and requiring large constants to be
materialised) just to use the overflow flag. It is simpler to just do the
saturation manually, using the higher bitwidth addition and a min/max against
the saturating bounds. That is what this patch attempts to do.

Differential Revision: https://reviews.llvm.org/D68926

llvm-svn: 375211

2019-10-18 09:47:48 +00:00

David Green

fe2d15b39b

[Codegen] Adjust saturation test. NFC.

Add some extra sat tests and adjust some of the existing tests to use signext where it would naturally be.

llvm-svn: 375009

2019-10-16 15:50:42 +00:00

2 Commits