On 11/19/23 18:22, Oleg Endo wrote:
On Sun, 2023-11-19 at 17:47 -0700, Jeff Law wrote:
This is work originally started by Joern @ Embecosm.
There's been a long standing sense that we're generating too many
sign/zero extensions on the RISC-V port. REE is useful, but it's really
focused on a relatively narrow part of the extension problem.
What Joern's patch does is introduce a new pass which tracks liveness of
chunks of pseudo regs. Specifically it tracks bits 0..7, 8..15, 16..31
and 32..63.
If it encounters a sign/zero extend that sets bits that are never read,
then it replaces the sign/zero extension with a narrowing subreg. The
narrowing subreg usually gets eliminated by subsequent passes (it's just
a copy after all).
Have you tried it on SH, too? (and if so any numbers?)
Just bootstrap with C regression testing on sh4/sh4eb. No data on
improvements.
Jeff
