cmd/compile: improve uint8/uint16 logical immediates on PPC64

Logical ops on uint8/uint16 (AND/OR/XOR) with constants sometimes
materialized the mask via MOVD (often as a negative immediate), even
when the value fit in the UI-immediate range. This prevented the backend
from selecting andi. / ori / xori forms.

This CL makes:
UI-immediate truncation is performed only at the use-site of
logical-immediate ops, and only when the constant does not fit in the
8- or 16-bit unsigned domain (m != uint8(m) / m != uint16(m)).

This avoids negative-mask materialization and enables correct emission of
UI-form logical instructions. Arithmetic SI-immediate instructions (addi, subfic, etc.) and other
use-patterns are unchanged.

Codegen tests are added to ensure the expected andi./ori/xori
patterns appear and that MOVD is not emitted for valid 8/16-bit masks.

Change-Id: I9fcdf4498c4e984c7587814fb9019a75865c4a0d
Cq-Include-Trybots: luci.golang.try:gotip-linux-ppc64_power10,gotip-linux-ppc64_power8,gotip-linux-ppc64le_power8,gotip-linux-ppc64le_power9,gotip-linux-ppc64le_power10
Reviewed-on: https://go-review.googlesource.com/c/go/+/704015
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Paul Murphy <paumurph@redhat.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Mark Freeman <markfreeman@google.com>

1 files changed, 31 insertions, 0 deletions

diff --git a/test/codegen/arithmetic.go b/test/codegen/arithmetic.go
index f8a2fc5400..a5a317b2d1 100644
--- a/test/codegen/arithmetic.go
+++ b/test/codegen/arithmetic.go
@@ -789,3 +789,34 @@ func Uint64Max(a, b uint64) uint64 {
 	// riscv64/rva22u64,riscv64/rva23u64:"MAXU"
 	return max(a, b)
 }
+
+// PPC64x: Canonicalization of uint8/uint16 logical immediates
+func U16And(v uint16) uint16 {
+	// ppc64x:"ANDCC [$]32768" -"MOVD"
+	return v & (1 << 15)
+}
+
+func U16Or(v uint16) uint16 {
+	// ppc64x:"OR[I]? [$]32768" -"MOVD"
+	return v | (1 << 15)
+}
+
+func U16Xor(v uint16) uint16 {
+	// ppc64x:"XOR[I]? [$]32768" -"MOVD"
+	return v ^ (1 << 15)
+}
+
+func U8And(v uint8) uint8 {
+	// ppc64x:"ANDCC [$]128" -"MOVD"
+	return v & (1 << 7)
+}
+
+func U8Or(v uint8) uint8 {
+	// ppc64x:"OR[I]? [$]128" -"MOVD"
+	return v | (1 << 7)
+}
+
+func U8Xor(v uint8) uint8 {
+	// ppc64x:"XOR[I]? [$]128" -"MOVD"
+	return v ^ (1 << 7)
+}