Kenneth Graunke
26bb81f3f6
This expression accidentally performs a 32-bit sign-extension when
processing the second half of the expression (the low 16 bits).
Consider -7W, which is represented as 0xfff9fff9 in our encoding (the
16-bit word is replicated to both halves of the 32-bit dword).
Tigerlake's compaction stores the low 11-bits of an immediate as-is,
and replicates the 12th bit. So here, compacted_imm will be 0xff9.
( (int)(0xff9 << 20) >> 4) |
((short)(0xff9 << 4) >> 4))
0xfff90000 | (0xff90 >> 4)
0xfff90000 | 0xfffffff9 ...oops...
0xfffffff9
By casting the second line of the expression to unsigned short, we
prevent the sign-extension when it combines both parts, so we get:
0xfff90000 | 0x0000fff9
0xfff9fff9
Fixes: 12d3b11908 ("intel/compiler: Add instruction compaction support on Gen12")
Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16833>
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