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

Authored by dmgreen on Oct 18 2019, 2:47 AM.

Description

[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

Details

Committed
dmgreenOct 18 2019, 2:47 AM
Differential Revision
D68926: [Codegen] Alter the default promotion for add_sat and sub_sat
Parents
rG0c7cc383e5b8: [AArch64][SVE] Implement unpack intrinsics
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