diff options
| author | Ilya Tocar <ilya.tocar@intel.com> | 2017-12-07 10:56:45 -0600 |
|---|---|---|
| committer | Ilya Tocar <ilya.tocar@intel.com> | 2018-02-14 19:56:57 +0000 |
| commit | de4edf3de7acda2cc7da8764ecdb3ff2e85c7a2d (patch) | |
| tree | 6151cc9d479bc3d684577b3a87c704d6c3aba7b0 /src | |
| parent | 9c4fd4626caefa0566e2d853c02912d559c01f62 (diff) | |
| download | go-de4edf3de7acda2cc7da8764ecdb3ff2e85c7a2d.tar.xz | |
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 <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Diffstat (limited to 'src')
| -rw-r--r-- | src/cmd/compile/internal/amd64/ssa.go | 8 |
1 files 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() } |