cmd/compile: remove redundant calls to cmpstring
The results of cmpstring are reuseable if the second call has the
same arguments and memory.
Note that this gets rid of cmpstring, but we still generate a
redundant </<= test and branch afterwards, because the compiler
doesn't know that cmpstring only ever returns -1,0,1.
Update #61725
Change-Id: I93a0d1ccca50d90b1e1a888240ffb75a3b10b59b
Reviewed-on: https://go-review.googlesource.com/c/go/+/578835
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
diff --git a/src/cmd/compile/internal/ssa/_gen/generic.rules b/src/cmd/compile/internal/ssa/_gen/generic.rules
index 4c475d3..398601e 100644
--- a/src/cmd/compile/internal/ssa/_gen/generic.rules
+++ b/src/cmd/compile/internal/ssa/_gen/generic.rules
@@ -2794,3 +2794,12 @@
(Load <t> (OffPtr [off] (Convert (Addr {sym} _) _) ) _) && t.IsInteger() && t.Size() == 4 && isFixed32(config, sym, off) => (Const32 [fixed32(config, sym, off)])
(Load <t> (OffPtr [off] (ITab (IMake (Addr {sym} _) _))) _) && t.IsInteger() && t.Size() == 4 && isFixed32(config, sym, off) => (Const32 [fixed32(config, sym, off)])
(Load <t> (OffPtr [off] (ITab (IMake (Convert (Addr {sym} _) _) _))) _) && t.IsInteger() && t.Size() == 4 && isFixed32(config, sym, off) => (Const32 [fixed32(config, sym, off)])
+
+// Calling cmpstring a second time with the same arguments in the
+// same memory state can reuse the results of the first call.
+// See issue 61725.
+// Note that this could pretty easily generalize to any pure function.
+(StaticLECall {f} x y m:(SelectN [1] c:(StaticLECall {g} x y mem)))
+ && isSameCall(f, "runtime.cmpstring")
+ && isSameCall(g, "runtime.cmpstring")
+=> (MakeResult (SelectN [0] <typ.Int> c) m)
diff --git a/src/cmd/compile/internal/ssa/rewritegeneric.go b/src/cmd/compile/internal/ssa/rewritegeneric.go
index 468e9fa..98c94bc 100644
--- a/src/cmd/compile/internal/ssa/rewritegeneric.go
+++ b/src/cmd/compile/internal/ssa/rewritegeneric.go
@@ -29311,6 +29311,36 @@
v.AddArg2(v0, mem)
return true
}
+ // match: (StaticLECall {f} x y m:(SelectN [1] c:(StaticLECall {g} x y mem)))
+ // cond: isSameCall(f, "runtime.cmpstring") && isSameCall(g, "runtime.cmpstring")
+ // result: (MakeResult (SelectN [0] <typ.Int> c) m)
+ for {
+ if len(v.Args) != 3 {
+ break
+ }
+ f := auxToCall(v.Aux)
+ _ = v.Args[2]
+ x := v.Args[0]
+ y := v.Args[1]
+ m := v.Args[2]
+ if m.Op != OpSelectN || auxIntToInt64(m.AuxInt) != 1 {
+ break
+ }
+ c := m.Args[0]
+ if c.Op != OpStaticLECall || len(c.Args) != 3 {
+ break
+ }
+ g := auxToCall(c.Aux)
+ if x != c.Args[0] || y != c.Args[1] || !(isSameCall(f, "runtime.cmpstring") && isSameCall(g, "runtime.cmpstring")) {
+ break
+ }
+ v.reset(OpMakeResult)
+ v0 := b.NewValue0(v.Pos, OpSelectN, typ.Int)
+ v0.AuxInt = int64ToAuxInt(0)
+ v0.AddArg(c)
+ v.AddArg2(v0, m)
+ return true
+ }
return false
}
func rewriteValuegeneric_OpStore(v *Value) bool {
diff --git a/src/cmp/cmp.go b/src/cmp/cmp.go
index 4d1af6a..a13834c 100644
--- a/src/cmp/cmp.go
+++ b/src/cmp/cmp.go
@@ -40,13 +40,19 @@
func Compare[T Ordered](x, y T) int {
xNaN := isNaN(x)
yNaN := isNaN(y)
- if xNaN && yNaN {
- return 0
- }
- if xNaN || x < y {
+ if xNaN {
+ if yNaN {
+ return 0
+ }
return -1
}
- if yNaN || x > y {
+ if yNaN {
+ return +1
+ }
+ if x < y {
+ return -1
+ }
+ if x > y {
return +1
}
return 0
diff --git a/test/codegen/comparisons.go b/test/codegen/comparisons.go
index 4edf930..e585045 100644
--- a/test/codegen/comparisons.go
+++ b/test/codegen/comparisons.go
@@ -6,7 +6,10 @@
package codegen
-import "unsafe"
+import (
+ "cmp"
+ "unsafe"
+)
// This file contains code generation tests related to the comparison
// operators.
@@ -801,3 +804,24 @@
// arm64:`CMP`,`CSET`,`CSEL`
return (p1.X-p3.X)*(p2.Y-p3.Y)-(p2.X-p3.X)*(p1.Y-p3.Y) < 0
}
+
+func cmpstring1(x, y string) int {
+ // amd64:".*cmpstring"
+ if x < y {
+ return -1
+ }
+ // amd64:-".*cmpstring"
+ if x > y {
+ return +1
+ }
+ return 0
+}
+func cmpstring2(x, y string) int {
+ // We want to fail if there are two calls to cmpstring.
+ // They will both have the same line number, so a test
+ // like in cmpstring1 will not work. Instead, we
+ // look for spill/restore instructions, which only
+ // need to exist if there are 2 calls.
+ //amd64:-`MOVQ\t.*\(SP\)`
+ return cmp.Compare(x, y)
+}
