cmd/compile: ppc64 fold (x+x)<<c into x<<(c+1)

On ppc64/ppc64le, rewrite (x + x) << c to x << (c+1) for constant shifts. This removes an ADD, shortens the dependency chain, and reduces code size.

Add rules for both 64-bit (SLDconst) and 32-bit (SLWconst), and extend
test/codegen/shift.go with ppc64x checks to assert a single SLD/SLW and
forbid ADD. Aligns ppc64 with other architectures that already assert
similar codegen in shift.go.

Change-Id: Ie564afbb029a5bd48887b82b0c455ca1dddd5508
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/+/712000
Reviewed-by: Archana Ravindar <aravinda@redhat.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/test/codegen/shift.go b/test/codegen/shift.go
index 4222b0b845..9ae113d9d7 100644
--- a/test/codegen/shift.go
+++ b/test/codegen/shift.go
@@ -123,6 +123,7 @@ func lshConst32x1Add(x int32) int32 {
 	// amd64:"SHLL [$]2"
 	// loong64:"SLL [$]2"
 	// riscv64:"SLLI [$]2"
+	// ppc64x:"SLW [$]2" -"ADD"
 	return (x + x) << 1
 }
 
@@ -130,6 +131,7 @@ func lshConst64x1Add(x int64) int64 {
 	// amd64:"SHLQ [$]2"
 	// loong64:"SLLV [$]2"
 	// riscv64:"SLLI [$]2"
+	// ppc64x:"SLD [$]2" -"ADD"
 	return (x + x) << 1
 }
 
@@ -137,6 +139,7 @@ func lshConst32x2Add(x int32) int32 {
 	// amd64:"SHLL [$]3"
 	// loong64:"SLL [$]3"
 	// riscv64:"SLLI [$]3"
+	// ppc64x:"SLW [$]3" -"ADD"
 	return (x + x) << 2
 }
 
@@ -144,12 +147,14 @@ func lshConst64x2Add(x int64) int64 {
 	// amd64:"SHLQ [$]3"
 	// loong64:"SLLV [$]3"
 	// riscv64:"SLLI [$]3"
+	// ppc64x:"SLD [$]3" -"ADD"
 	return (x + x) << 2
 }
 
 func lshConst32x31Add(x int32) int32 {
 	// loong64:-"SLL " "MOVV R0"
 	// riscv64:-"SLLI" "MOV [$]0"
+	// ppc64x:"ADD" "SLW [$]31" -"SLW [$]32"
 	return (x + x) << 31
 }