cmd/gc: faster code, mainly for rotate

* Eliminate bounds check on known small shifts.
* Rewrite x<<s | x>>(32-s) as a rotate (constant s).
* More aggressive (but still minimal) range analysis.

R=ken, dave, iant
CC=golang-dev
https://golang.org/cl/6209077

1 files changed, 141 insertions, 0 deletions

diff --git a/test/rotate.go b/test/rotate.go
new file mode 100644
index 0000000000..67d32d7ac2
--- /dev/null
+++ b/test/rotate.go
@@ -0,0 +1,141 @@
+// $G $D/$F.go && $L $F.$A &&
+// ./$A.out >tmp.go && $G tmp.go && $L -o $A.out1 tmp.$A && ./$A.out1
+// rm -f tmp.go $A.out1
+
+// Copyright 2012 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Generate test of shift and rotate by constants.
+// The output is compiled and run.
+//
+// The output takes around a minute to compile, link, and run
+// but it is only done during ./run, not in normal builds using run.go.
+
+package main
+
+import (
+	"bufio"
+	"flag"
+	"fmt"
+	"os"
+)
+
+func main() {
+	flag.Parse()
+
+	b := bufio.NewWriter(os.Stdout)
+	defer b.Flush()
+
+	fmt.Fprintf(b, "%s\n", prolog)
+
+	for logBits := uint(3); logBits <= 6; logBits++ {
+		for mode := 0; mode < 1<<2; mode++ {
+			gentest(b, 1<<logBits, mode&1 != 0, mode&2 != 0)
+		}
+	}
+}
+
+const prolog = `
+
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+var (
+	i8 int8 = 0x12
+	i16 int16 = 0x1234
+	i32 int32 = 0x12345678
+	i64 int64 = 0x123456789abcdef0
+	ui8 uint8 = 0x12
+	ui16 uint16 = 0x1234
+	ui32 uint32 = 0x12345678
+	ui64 uint64 = 0x123456789abcdef0
+
+	ni8 = ^i8
+	ni16 = ^i16
+	ni32 = ^i32
+	ni64 = ^i64
+	nui8 = ^ui8
+	nui16 = ^ui16
+	nui32 = ^ui32
+	nui64 = ^ui64
+)
+
+var nfail = 0
+
+func check(desc string, have, want interface{}) {
+	if have != want {
+		nfail++
+		fmt.Printf("%s = %T(%#x), want %T(%#x)\n", desc, have, have, want, want)
+		if nfail >= 100 {
+			fmt.Printf("BUG: stopping after 100 failures\n")
+			os.Exit(0)
+		}
+	}
+}
+
+func main() {
+	if nfail > 0 {
+		fmt.Printf("BUG\n")
+	}
+}
+
+`
+
+func gentest(b *bufio.Writer, bits uint, unsigned, inverted bool) {
+	fmt.Fprintf(b, "func init() {\n")
+	defer fmt.Fprintf(b, "}\n")
+	n := 0
+
+	// Generate tests for left/right and right/left.
+	for l := uint(0); l <= bits; l++ {
+		for r := uint(0); r <= bits; r++ {
+			typ := fmt.Sprintf("int%d", bits)
+			v := fmt.Sprintf("i%d", bits)
+			if unsigned {
+				typ = "u" + typ
+				v = "u" + v
+			}
+			v0 := int64(0x123456789abcdef0)
+			if inverted {
+				v = "n" + v
+				v0 = ^v0
+			}
+			expr1 := fmt.Sprintf("%s<<%d | %s>>%d", v, l, v, r)
+			expr2 := fmt.Sprintf("%s>>%d | %s<<%d", v, r, v, l)
+			
+			var result string
+			if unsigned {
+				v := uint64(v0) >> (64 - bits)
+				v = v<<l | v>>r
+				v <<= 64 - bits
+				v >>= 64 - bits
+				result = fmt.Sprintf("%#x", v)
+			} else {
+				v := int64(v0) >> (64 - bits)
+				v = v<<l | v>>r
+				v <<= 64 - bits
+				v >>= 64 - bits
+				result = fmt.Sprintf("%#x", v)
+			}
+
+			fmt.Fprintf(b, "\tcheck(%q, %s, %s(%s))\n", expr1, expr1, typ, result)
+			fmt.Fprintf(b, "\tcheck(%q, %s, %s(%s))\n", expr2, expr2, typ, result)
+
+			// Chop test into multiple functions so that there's not one
+			// enormous function to compile/link.
+			// All the functions are named init so we don't have to do
+			// anything special to call them.  ☺
+			if n++; n >= 100 {
+				fmt.Fprintf(b, "}\n")
+				fmt.Fprintf(b, "func init() {\n")
+				n = 0
+			}
+		}
+	}
+}
+