cmd/compile: handle more cases in isNonNegative

The gains from this aren't particularly impressive.
Still, it is cheap and easy, and
it will keep me from wondering about whether it
might help to add X every time I look at this function.

This updated function is pretty exhaustive;
I examined every op encountered in a call to isNonNegative
when compiling all the stuff hanging around in my GOPATH,
for both 386 and amd64.

(32 bit architectures were somewhat neglected before.)

Object file size impact, 64 bit:

file                       before    after     Δ       %       
archive/zip.a              359352    359284    -68     -0.019% 
cmd/compile/internal/ssa.a 30715960  30717526  +1566   +0.005% 
cmd/internal/obj/arm64.a   2972532   2972440   -92     -0.003% 
cmd/internal/obj/riscv.a   297714    297672    -42     -0.014% 
debug/dwarf.a              656336    655346    -990    -0.151% 
debug/gosym.a              183352    183122    -230    -0.125% 
encoding/gob.a             901130    900798    -332    -0.037% 
image/gif.a                171884    171890    +6      +0.003% 
internal/trace.a           506930    507270    +340    +0.067% 
math.a                     233506    233490    -16     -0.007% 
reflect.a                  1431740   1431476   -264    -0.018% 
runtime.a                  3854480   3854332   -148    -0.004% 
unicode/utf16.a            8920      8980      +60     +0.673% 
total                      133000610 133000400 -210    -0.000% 

Object file size impact, 32 bit:

file                                          before    after     Δ       %       
archive/zip.a                                 330794    329640    -1154   -0.349% 
cmd/compile/internal/gc.a                     8090204   8090026   -178    -0.002% 
cmd/compile/internal/ssa.a                    29392460  29393890  +1430   +0.005% 
cmd/internal/goobj2.a                         189512    189492    -20     -0.011% 
cmd/internal/obj/arm64.a                      2444942   2444860   -82     -0.003% 
cmd/internal/obj/riscv.a                      272848    272806    -42     -0.015% 
cmd/link/internal/loader.a                    388548    388544    -4      -0.001% 
cmd/link/internal/loadpe.a                    158776    158684    -92     -0.058% 
cmd/vendor/golang.org/x/arch/ppc64/ppc64asm.a 511824    511316    -508    -0.099% 
cmd/vendor/golang.org/x/arch/x86/x86asm.a     512812    512704    -108    -0.021% 
cmd/vendor/golang.org/x/sys/unix.a            942422    942218    -204    -0.022% 
compress/bzip2.a                              88768     88680     -88     -0.099% 
crypto/tls.a                                  1655542   1655396   -146    -0.009% 
debug/dwarf.a                                 608520    605822    -2698   -0.443% 
debug/gosym.a                                 168282    168276    -6      -0.004% 
debug/pe.a                                    173146    173108    -38     -0.022% 
encoding/gob.a                                797978    797724    -254    -0.032% 
encoding/hex.a                                44080     44020     -60     -0.136% 
image/gif.a                                   152142    152148    +6      +0.004% 
internal/xcoff.a                              186480    185834    -646    -0.346% 
math.a                                        257866    257854    -12     -0.005% 
net/http.a                                    3588246   3588150   -96     -0.003% 
net/textproto.a                               162384    162120    -264    -0.163% 
reflect.a                                     1316204   1316058   -146    -0.011% 
regexp.a                                      373346    373248    -98     -0.026% 
runtime/pprof.a                               345318    345088    -230    -0.067% 
runtime.a                                     3513902   3513714   -188    -0.005% 
syscall.a                                     781406    781018    -388    -0.050% 
time.a                                        483814    483750    -64     -0.013% 
unicode/utf16.a                               8394      8364      -30     -0.357% 
vendor/golang.org/x/crypto/cryptobyte.a       287100    286706    -394    -0.137% 
vendor/golang.org/x/net/route.a               175042    174724    -318    -0.182% 
total                                         121677354 121670234 -7120   -0.006% 

Change-Id: Ie672752feb5e94dd151836f852181980710e820d
Reviewed-on: https://go-review.googlesource.com/c/go/+/212777
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/ssa/prove.go

@@ -1296,6 +1296,13 @@ func removeBranch(b *Block, branch branch) {
 
 // isNonNegative reports whether v is known to be greater or equal to zero.
 func isNonNegative(v *Value) bool {
+	if !v.Type.IsInteger() {
+		panic("isNonNegative bad type")
+	}
+	if !v.Type.IsSigned() {
+		return true
+	}
+
 	switch v.Op {
 	case OpConst64:
 		return v.AuxInt >= 0
@@ -1303,16 +1310,37 @@ func isNonNegative(v *Value) bool {
 	case OpConst32:
 		return int32(v.AuxInt) >= 0
 
+	case OpConst16:
+		return int16(v.AuxInt) >= 0
+
+	case OpConst8:
+		return int8(v.AuxInt) >= 0
+
 	case OpStringLen, OpSliceLen, OpSliceCap,
-		OpZeroExt8to64, OpZeroExt16to64, OpZeroExt32to64:
+		OpZeroExt8to64, OpZeroExt16to64, OpZeroExt32to64,
+		OpZeroExt8to32, OpZeroExt16to32, OpZeroExt8to16,
+		OpCtz64, OpCtz32, OpCtz16, OpCtz8:
 		return true
 
-	case OpRsh64Ux64:
+	case OpRsh64Ux64, OpRsh32Ux64:
 		by := v.Args[1]
 		return by.Op == OpConst64 && by.AuxInt > 0
 
-	case OpRsh64x64:
+	case OpRsh64x64, OpRsh32x64, OpRsh8x64, OpRsh16x64, OpRsh32x32, OpRsh64x32,
+		OpSignExt32to64, OpSignExt16to64, OpSignExt8to64, OpSignExt16to32, OpSignExt8to32:
 		return isNonNegative(v.Args[0])
+
+	case OpAnd64, OpAnd32, OpAnd16, OpAnd8:
+		return isNonNegative(v.Args[0]) || isNonNegative(v.Args[1])
+
+	case OpMod64, OpMod32, OpMod16, OpMod8,
+		OpDiv64, OpDiv32, OpDiv16, OpDiv8,
+		OpOr64, OpOr32, OpOr16, OpOr8,
+		OpXor64, OpXor32, OpXor16, OpXor8:
+		return isNonNegative(v.Args[0]) && isNonNegative(v.Args[1])
+
+		// We could handle OpPhi here, but the improvements from doing
+		// so are very minor, and it is neither simple nor cheap.
 	}
 	return false
 }