cmd/compile: rewrite 2*x+c into LEAx1 on amd64

Rewrite x<<1+c into x+x+c, which can be expressed as a single LEAQ/LEAL.

Bit of a special case, but the single-instruction
LEA is both shorter and faster than SHL then ADD.

Triggers 293 times during make.bash.

Change-Id: I3f09c8e9a8f3859d1eeed336f095fc3ada79c2c1
Reviewed-on: https://go-review.googlesource.com/108938
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

diff --git a/src/cmd/compile/internal/ssa/gen/AMD64.rules b/src/cmd/compile/internal/ssa/gen/AMD64.rules
index 482a1558dcce14f1939c9de054880e1cdb9fae4d..cab0f660799d7ac01488fa05c718ad1d76885dcb 100644 (file)
--- a/src/cmd/compile/internal/ssa/gen/AMD64.rules
+++ b/src/cmd/compile/internal/ssa/gen/AMD64.rules
@@ -925,6 +925,7 @@
 // combine ADDQ/ADDQconst into LEAQ1
 (ADDQconst [c] (ADDQ x y)) -> (LEAQ1 [c] x y)
 (ADDQ (ADDQconst [c] x) y) -> (LEAQ1 [c] x y)
+(ADD(Q|L)const [c] (SHL(Q|L)const [1] x)) -> (LEA(Q|L)1 [c] x x)
 
 // fold ADDQ into LEAQ
 (ADDQconst [c] (LEAQ [d] {s} x)) && is32Bit(c+d) -> (LEAQ [c+d] {s} x)

diff --git a/src/cmd/compile/internal/ssa/rewriteAMD64.go b/src/cmd/compile/internal/ssa/rewriteAMD64.go
index e51a25527c6bcd9264994739fd4b3002f29991f7..313b6bef9c39dfdb2f074b041dae98280cf7a3c6 100644 (file)
--- a/src/cmd/compile/internal/ssa/rewriteAMD64.go
+++ b/src/cmd/compile/internal/ssa/rewriteAMD64.go
@@ -26,7 +26,7 @@ func rewriteValueAMD64(v *Value) bool {
        case OpAMD64ADDQ:
                return rewriteValueAMD64_OpAMD64ADDQ_0(v) || rewriteValueAMD64_OpAMD64ADDQ_10(v) || rewriteValueAMD64_OpAMD64ADDQ_20(v)
        case OpAMD64ADDQconst:
-               return rewriteValueAMD64_OpAMD64ADDQconst_0(v)
+               return rewriteValueAMD64_OpAMD64ADDQconst_0(v) || rewriteValueAMD64_OpAMD64ADDQconst_10(v)
        case OpAMD64ADDQconstmem:
                return rewriteValueAMD64_OpAMD64ADDQconstmem_0(v)
        case OpAMD64ADDQmem:
@@ -1313,6 +1313,25 @@ func rewriteValueAMD64_OpAMD64ADDL_10(v *Value) bool {
        return false
 }
 func rewriteValueAMD64_OpAMD64ADDLconst_0(v *Value) bool {
+       // match: (ADDLconst [c] (SHLLconst [1] x))
+       // cond:
+       // result: (LEAL1 [c] x x)
+       for {
+               c := v.AuxInt
+               v_0 := v.Args[0]
+               if v_0.Op != OpAMD64SHLLconst {
+                       break
+               }
+               if v_0.AuxInt != 1 {
+                       break
+               }
+               x := v_0.Args[0]
+               v.reset(OpAMD64LEAL1)
+               v.AuxInt = c
+               v.AddArg(x)
+               v.AddArg(x)
+               return true
+       }
        // match: (ADDLconst [c] x)
        // cond: int32(c)==0
        // result: x
@@ -2077,6 +2096,25 @@ func rewriteValueAMD64_OpAMD64ADDQconst_0(v *Value) bool {
                v.AddArg(y)
                return true
        }
+       // match: (ADDQconst [c] (SHLQconst [1] x))
+       // cond:
+       // result: (LEAQ1 [c] x x)
+       for {
+               c := v.AuxInt
+               v_0 := v.Args[0]
+               if v_0.Op != OpAMD64SHLQconst {
+                       break
+               }
+               if v_0.AuxInt != 1 {
+                       break
+               }
+               x := v_0.Args[0]
+               v.reset(OpAMD64LEAQ1)
+               v.AuxInt = c
+               v.AddArg(x)
+               v.AddArg(x)
+               return true
+       }
        // match: (ADDQconst [c] (LEAQ [d] {s} x))
        // cond: is32Bit(c+d)
        // result: (LEAQ [c+d] {s} x)
@@ -2240,6 +2278,9 @@ func rewriteValueAMD64_OpAMD64ADDQconst_0(v *Value) bool {
                v.AddArg(x)
                return true
        }
+       return false
+}
+func rewriteValueAMD64_OpAMD64ADDQconst_10(v *Value) bool {
        // match: (ADDQconst [off] x:(SP))
        // cond:
        // result: (LEAQ [off] x)

diff --git a/test/codegen/arithmetic.go b/test/codegen/arithmetic.go
index ce7a7c27f4a98155547a3edeb98098783c48602b..3948ef301d61d9d48d8222189a33ca8523ee5bcd 100644 (file)
--- a/test/codegen/arithmetic.go
+++ b/test/codegen/arithmetic.go
@@ -173,3 +173,8 @@ func CapMod(a []int) int {
        // amd64:"ANDQ\t[$]4095"
        return cap(a) % ((1 << 11) + 2048)
 }
+
+func AddMul(x int) int {
+       // amd64:"LEAQ\t1"
+       return 2*x + 1
+}