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| author | Alexandru Moșoi <brtzsnr@gmail.com> | 2016-04-05 23:32:49 +0200 |
|---|---|---|
| committer | Alexandru Moșoi <alexandru@mosoi.ro> | 2016-04-07 13:28:13 +0000 |
| commit | 8448d3aace7f26bd6eca14e8b89c5a981c2ab9d3 (patch) | |
| tree | 1a01cc1444c82e3e66cd194cefca29b7e02a2471 /src | |
| parent | 121c434f7add815c3147b01a097a8998018bcc6b (diff) | |
| download | go-8448d3aace7f26bd6eca14e8b89c5a981c2ab9d3.tar.xz | |
cmd/compile: fold CMPconst and SHR
Fold the comparison when the SHR result is small.
Useful for:
- murmur mix like hashing where higher bits are desirable, i.e. hash = uint32(i * C) >> 18
- integer log2 via DeBruijn sequence: http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogDeBruijn
Change-Id: If70ae18cb86f4cc83ab6213f88ced03cc4986156
Reviewed-on: https://go-review.googlesource.com/21514
Run-TryBot: Alexandru Moșoi <alexandru@mosoi.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Diffstat (limited to 'src')
| -rw-r--r-- | src/cmd/compile/internal/ssa/gen/AMD64.rules | 2 | ||||
| -rw-r--r-- | src/cmd/compile/internal/ssa/rewriteAMD64.go | 32 |
2 files changed, 34 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/ssa/gen/AMD64.rules b/src/cmd/compile/internal/ssa/gen/AMD64.rules index b37720eb39..d7f361dc2e 100644 --- a/src/cmd/compile/internal/ssa/gen/AMD64.rules +++ b/src/cmd/compile/internal/ssa/gen/AMD64.rules @@ -1101,6 +1101,8 @@ (CMPQconst (MOVBQZX _) [c]) && 0xFF < c -> (FlagLT_ULT) (CMPQconst (MOVWQZX _) [c]) && 0xFFFF < c -> (FlagLT_ULT) (CMPQconst (MOVLQZX _) [c]) && 0xFFFFFFFF < c -> (FlagLT_ULT) +(CMPLconst (SHRLconst _ [c]) [n]) && 0 <= n && 0 < c && c <= 32 && (1<<uint64(32-c)) <= uint64(n) -> (FlagLT_ULT) +(CMPQconst (SHRQconst _ [c]) [n]) && 0 <= n && 0 < c && c <= 64 && (1<<uint64(64-c)) <= uint64(n) -> (FlagLT_ULT) (CMPQconst (ANDQconst _ [m]) [n]) && 0 <= m && m < n -> (FlagLT_ULT) (CMPLconst (ANDLconst _ [m]) [n]) && 0 <= int32(m) && int32(m) < int32(n) -> (FlagLT_ULT) (CMPWconst (ANDWconst _ [m]) [n]) && 0 <= int16(m) && int16(m) < int16(n) -> (FlagLT_ULT) diff --git a/src/cmd/compile/internal/ssa/rewriteAMD64.go b/src/cmd/compile/internal/ssa/rewriteAMD64.go index a1d1e4edd9..34a393bbc5 100644 --- a/src/cmd/compile/internal/ssa/rewriteAMD64.go +++ b/src/cmd/compile/internal/ssa/rewriteAMD64.go @@ -2869,6 +2869,22 @@ func rewriteValueAMD64_OpAMD64CMPLconst(v *Value, config *Config) bool { v.reset(OpAMD64FlagGT_UGT) return true } + // match: (CMPLconst (SHRLconst _ [c]) [n]) + // cond: 0 <= n && 0 < c && c <= 32 && (1<<uint64(32-c)) <= uint64(n) + // result: (FlagLT_ULT) + for { + v_0 := v.Args[0] + if v_0.Op != OpAMD64SHRLconst { + break + } + c := v_0.AuxInt + n := v.AuxInt + if !(0 <= n && 0 < c && c <= 32 && (1<<uint64(32-c)) <= uint64(n)) { + break + } + v.reset(OpAMD64FlagLT_ULT) + return true + } // match: (CMPLconst (ANDLconst _ [m]) [n]) // cond: 0 <= int32(m) && int32(m) < int32(n) // result: (FlagLT_ULT) @@ -3107,6 +3123,22 @@ func rewriteValueAMD64_OpAMD64CMPQconst(v *Value, config *Config) bool { v.reset(OpAMD64FlagLT_ULT) return true } + // match: (CMPQconst (SHRQconst _ [c]) [n]) + // cond: 0 <= n && 0 < c && c <= 64 && (1<<uint64(64-c)) <= uint64(n) + // result: (FlagLT_ULT) + for { + v_0 := v.Args[0] + if v_0.Op != OpAMD64SHRQconst { + break + } + c := v_0.AuxInt + n := v.AuxInt + if !(0 <= n && 0 < c && c <= 64 && (1<<uint64(64-c)) <= uint64(n)) { + break + } + v.reset(OpAMD64FlagLT_ULT) + return true + } // match: (CMPQconst (ANDQconst _ [m]) [n]) // cond: 0 <= m && m < n // result: (FlagLT_ULT) |