cmd/internal/obj/riscv: simplify addition with constant

This CL simplifies riscv addition (add r, imm) to
(ADDI (ADDI r, imm/2), imm-imm/2) if imm is in specific ranges.
(-4096 <= imm <= -2049 or 2048 <= imm <= 4094)

There is little impact to the go1 benchmark, while the total
size of pkg/linux_riscv64 decreased by about 11KB.

Change-Id: I236eb8af3b83bb35ce9c0b318fc1d235e8ab9a4e
GitHub-Last-Rev: a2f56a07635344a40d6b8a9571f236743122be34
GitHub-Pull-Request: golang/go#48110
Reviewed-on: https://go-review.googlesource.com/c/go/+/346689
Run-TryBot: Ben Shi <powerman1st@163.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Joel Sing <joel@sing.id.au>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Michael Munday <mike.munday@lowrisc.org>

diff --git a/src/cmd/internal/obj/riscv/obj.go b/src/cmd/internal/obj/riscv/obj.go
index 73f62c007dd8ac7a4008f809f7877a2332b4a52e..6de967319c4615b1c2344b9cb307031ef339901d 100644 (file)
--- a/src/cmd/internal/obj/riscv/obj.go
+++ b/src/cmd/internal/obj/riscv/obj.go
@@ -774,6 +774,27 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
                                break // no need to split
                        }
 
+                       // Split into two additions if possible.
+                       imm := q.From.Offset
+                       const minInt12, maxInt12 = -(1 << 11), (1 << 11) - 1
+                       if q.As == AADDI && 2*minInt12 <= imm && imm <= 2*maxInt12 {
+                               imm0, imm1 := imm/2, imm-imm/2
+                               // ADDI $(imm/2), REG, TO
+                               p.Spadj = 0 // needed if TO is SP
+                               p.As = AADDI
+                               p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: imm0}
+                               p.Reg = q.Reg
+                               p.To = q.To
+                               p = obj.Appendp(p, newprog)
+                               // ADDI $(imm-imm/2), TO, TO
+                               p.Spadj = q.Spadj
+                               p.As = AADDI
+                               p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: imm1}
+                               p.Reg = q.To.Reg
+                               p.To = q.To
+                               break
+                       }
+
                        p.As = ALUI
                        p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: high}
                        p.Reg = 0

diff --git a/test/codegen/arithmetic.go b/test/codegen/arithmetic.go
index eb95416b6aabe38725a79ad3daf4615c4fc31991..754c5c9bc97da7aa65bde19311e2d6d0274b73a8 100644 (file)
--- a/test/codegen/arithmetic.go
+++ b/test/codegen/arithmetic.go
@@ -575,3 +575,11 @@ func constantFold3(i, j int) int {
        r := (5 * i) * (6 * j)
        return r
 }
+
+func addConst(i int64) (int64, int64) {
+       // riscv64:`ADDI`,-`LUI`
+       a := i + 3001
+       // riscv64:`LUI`,`ADDIW`
+       b := i + 5009
+       return a, b
+}