arch-gcn3: Fix sign extension for branches with multiplied offset

Certain branch instructions specify that the result of (simm16 * 4)
gets sign-extended before being added to the PC.

Previously, that result was being sign extended as if it was still a
16-bit number. This patch fixes that by having the result be sign
extended as an 18-bit number.

Change-Id: Id4d430f8daa71ca7910b570e7e39790626f1decf
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/41053
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Reviewed-by: Matthew Poremba <matthew.poremba@amd.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed