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cmd/compile/internal/ssa: emit IMUL3{L/Q} for MUL{L/Q}const on x86

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cmd/asm now supports three-operand form of IMUL,
so instead of using IMUL with resultInArg0, emit IMUL3 instruction.

This results in less redundant MOVs where SSA assigns
different registers to input[0] and dst arguments.

Note: these have exactly the same encoding when reg0=reg1:
      IMUL3x $const, reg0, reg1
      IMULx $const, reg
Two-operand IMULx is like a crippled IMUL3x, with dst fixed to input[0].
This is why we don't bother to generate IMULx for the case where
dst is the same as input[0].

Change-Id: I4becda475b3dffdd07b6fdf1c75bacc82af654e4
Reviewed-on: https://go-review.googlesource.com/99656
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Giovanni Bajo <rasky@develer.com>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
isharipo 2018-03-09 23:09:46 +03:00 • committed by Ilya Tocar
parent 080187f4f7
commit 85a8d25d53
6 changed files with 14 additions and 31 deletions
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9
src/cmd/compile/internal/x86/ssa.go
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@ -335,19 +335,12 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
case ssa.Op386MULLconst:
r := v.Reg()
if r != v.Args[0].Reg() {
v.Fatalf("input[0] and output not in same register %s", v.LongString())
}
p := s.Prog(v.Op.Asm())
p.From.Type = obj.TYPE_CONST
p.From.Offset = v.AuxInt
p.To.Type = obj.TYPE_REG
p.To.Reg = r
// TODO: Teach doasm to compile the three-address multiply imul $c, r1, r2
// then we don't need to use resultInArg0 for these ops.
//p.From3 = new(obj.Addr)
//p.From3.Type = obj.TYPE_REG
//p.From3.Reg = v.Args[0].Reg()
p.SetFrom3(obj.Addr{Type: obj.TYPE_REG, Reg: v.Args[0].Reg()})
case ssa.Op386SUBLconst,
ssa.Op386ADCLconst,