From de4edf3de7acda2cc7da8764ecdb3ff2e85c7a2d Mon Sep 17 00:00:00 2001 From: Ilya Tocar Date: Thu, 7 Dec 2017 10:56:45 -0600 Subject: [PATCH] cmd/compile/internal/amd64: update popcnt code generation Popcnt has false dependency on output register and generates MOVQ $0, reg to break it. But recently we switched MOVQ $0, reg encoding from xor reg, reg to actual mov $0, reg. This CL updates code generation for popcnt to use actual XOR. Change-Id: I4c1fc11e85758b53ba2679165fa55614ec54b27d Reviewed-on: https://go-review.googlesource.com/82516 Run-TryBot: Ilya Tocar TryBot-Result: Gobot Gobot Reviewed-by: Keith Randall --- src/cmd/compile/internal/amd64/ssa.go | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/src/cmd/compile/internal/amd64/ssa.go b/src/cmd/compile/internal/amd64/ssa.go index e3129edbf1..49ef415e66 100644 --- a/src/cmd/compile/internal/amd64/ssa.go +++ b/src/cmd/compile/internal/amd64/ssa.go @@ -867,10 +867,10 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) { case ssa.OpAMD64POPCNTQ, ssa.OpAMD64POPCNTL: if v.Args[0].Reg() != v.Reg() { // POPCNT on Intel has a false dependency on the destination register. - // Zero the destination to break the dependency. - p := s.Prog(x86.AMOVQ) - p.From.Type = obj.TYPE_CONST - p.From.Offset = 0 + // Xor register with itself to break the dependency. + p := s.Prog(x86.AXORQ) + p.From.Type = obj.TYPE_REG + p.From.Reg = v.Reg() p.To.Type = obj.TYPE_REG p.To.Reg = v.Reg() }