1
0
mirror of https://github.com/golang/go synced 2024-11-21 13:14:40 -07:00

6g, 8g: divide corner case

Fixes #1772.

R=ken2
CC=golang-dev
https://golang.org/cl/4798062
This commit is contained in:
Russ Cox 2011-07-28 14:18:22 -04:00
parent fe206e63ca
commit 08bfb39515
3 changed files with 160 additions and 17 deletions

View File

@ -436,9 +436,6 @@ samereg(Node *a, Node *b)
/*
* generate division.
* caller must set:
* ax = allocated AX register
* dx = allocated DX register
* generates one of:
* res = nl / nr
* res = nl % nr
@ -447,17 +444,35 @@ samereg(Node *a, Node *b)
void
dodiv(int op, Node *nl, Node *nr, Node *res)
{
int a;
Node n3, n4;
int a, check;
Node n3, n4, n5;
Type *t;
Node ax, dx, oldax, olddx;
Prog *p1, *p2, *p3;
// Have to be careful about handling
// most negative int divided by -1 correctly.
// The hardware will trap.
// Also the byte divide instruction needs AH,
// which we otherwise don't have to deal with.
// Easiest way to avoid for int8, int16: use int32.
// For int32 and int64, use explicit test.
// Could use int64 hw for int32.
t = nl->type;
if(t->width == 1) {
check = 0;
if(issigned[t->etype]) {
check = 1;
if(isconst(nl, CTINT) && mpgetfix(nl->val.u.xval) != -1LL<<(t->width*8-1))
check = 0;
else if(isconst(nr, CTINT) && mpgetfix(nr->val.u.xval) != -1)
check = 0;
}
if(t->width < 4) {
if(issigned[t->etype])
t = types[TINT32];
else
t = types[TUINT32];
check = 0;
}
a = optoas(op, t);
@ -473,6 +488,31 @@ dodiv(int op, Node *nl, Node *nr, Node *res)
savex(D_AX, &ax, &oldax, res, t);
cgen(nl, &ax);
}
p3 = P;
if(check) {
nodconst(&n4, t, -1);
gins(optoas(OCMP, t), &n3, &n4);
p1 = gbranch(optoas(ONE, t), T);
nodconst(&n4, t, -1LL<<(t->width*8-1));
if(t->width == 8) {
n5 = n4;
regalloc(&n4, t, N);
gins(AMOVQ, &n5, &n4);
}
gins(optoas(OCMP, t), &ax, &n4);
p2 = gbranch(optoas(ONE, t), T);
if(op == ODIV)
gmove(&n4, res);
if(t->width == 8)
regfree(&n4);
if(op == OMOD) {
nodconst(&n4, t, 0);
gmove(&n4, res);
}
p3 = gbranch(AJMP, T);
patch(p1, pc);
patch(p2, pc);
}
savex(D_DX, &dx, &olddx, res, t);
if(!issigned[t->etype]) {
nodconst(&n4, t, 0);
@ -481,13 +521,14 @@ dodiv(int op, Node *nl, Node *nr, Node *res)
gins(optoas(OEXTEND, t), N, N);
gins(a, &n3, N);
regfree(&n3);
if(op == ODIV)
gmove(&ax, res);
else
gmove(&dx, res);
restx(&ax, &oldax);
restx(&dx, &olddx);
if(check)
patch(p3, pc);
restx(&ax, &oldax);
}
/*

View File

@ -480,12 +480,40 @@ samereg(Node *a, Node *b)
* according to op.
*/
void
dodiv(int op, Type *t, Node *nl, Node *nr, Node *res, Node *ax, Node *dx)
dodiv(int op, Node *nl, Node *nr, Node *res, Node *ax, Node *dx)
{
Node n1, t1, t2, nz;
int check;
Node n1, t1, t2, n4, nz;
Type *t;
Prog *p1, *p2, *p3;
tempname(&t1, nl->type);
tempname(&t2, nr->type);
// Have to be careful about handling
// most negative int divided by -1 correctly.
// The hardware will trap.
// Also the byte divide instruction needs AH,
// which we otherwise don't have to deal with.
// Easiest way to avoid for int8, int16: use int32.
// For int32 and int64, use explicit test.
// Could use int64 hw for int32.
t = nl->type;
check = 0;
if(issigned[t->etype]) {
check = 1;
if(isconst(nl, CTINT) && mpgetfix(nl->val.u.xval) != -1LL<<(t->width*8-1))
check = 0;
else if(isconst(nr, CTINT) && mpgetfix(nr->val.u.xval) != -1)
check = 0;
}
if(t->width < 4) {
if(issigned[t->etype])
t = types[TINT32];
else
t = types[TUINT32];
check = 0;
}
tempname(&t1, t);
tempname(&t2, t);
cgen(nl, &t1);
cgen(nr, &t2);
@ -495,6 +523,24 @@ dodiv(int op, Type *t, Node *nl, Node *nr, Node *res, Node *ax, Node *dx)
regalloc(&n1, t, N);
gmove(&t2, &n1);
gmove(&t1, ax);
p3 = P;
if(check) {
nodconst(&n4, t, -1);
gins(optoas(OCMP, t), &n1, &n4);
p1 = gbranch(optoas(ONE, t), T);
nodconst(&n4, t, -1LL<<(t->width*8-1));
gins(optoas(OCMP, t), ax, &n4);
p2 = gbranch(optoas(ONE, t), T);
if(op == ODIV)
gmove(&n4, res);
if(op == OMOD) {
nodconst(&n4, t, 0);
gmove(&n4, res);
}
p3 = gbranch(AJMP, T);
patch(p1, pc);
patch(p2, pc);
}
if(!issigned[t->etype]) {
nodconst(&nz, t, 0);
gmove(&nz, dx);
@ -507,6 +553,8 @@ dodiv(int op, Type *t, Node *nl, Node *nr, Node *res, Node *ax, Node *dx)
gmove(ax, res);
else
gmove(dx, res);
if(check)
patch(p3, pc);
}
static void
@ -553,13 +601,13 @@ cgen_div(int op, Node *nl, Node *nr, Node *res)
if(is64(nl->type))
fatal("cgen_div %T", nl->type);
t = nl->type;
if(t->width == 1)
t = types[t->etype+2]; // int8 -> int16, uint8 -> uint16
if(issigned[nl->type->etype])
t = types[TINT32];
else
t = types[TUINT32];
savex(D_AX, &ax, &oldax, res, t);
savex(D_DX, &dx, &olddx, res, t);
dodiv(op, t, nl, nr, res, &ax, &dx);
dodiv(op, nl, nr, res, &ax, &dx);
restx(&dx, &olddx);
restx(&ax, &oldax);
}

54
test/divide.go Normal file
View File

@ -0,0 +1,54 @@
// $G $D/$F.go && $L $F.$A && ./$A.out
// Copyright 2011 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.
// divide corner cases
package main
import "fmt"
func f8(x, y, q, r int8) {
if t := x / y; t != q {
fmt.Printf("%d/%d = %d, want %d\n", x, y, t, q)
}
if t := x % y; t != r {
fmt.Printf("%d%%%d = %d, want %d\n", x, y, t, r)
}
}
func f16(x, y, q, r int16) {
if t := x / y; t != q {
fmt.Printf("%d/%d = %d, want %d\n", x, y, t, q)
}
if t := x % y; t != r {
fmt.Printf("%d%%%d = %d, want %d\n", x, y, t, r)
}
}
func f32(x, y, q, r int32) {
if t := x / y; t != q {
fmt.Printf("%d/%d = %d, want %d\n", x, y, t, q)
}
if t := x % y; t != r {
fmt.Printf("%d%%%d = %d, want %d\n", x, y, t, r)
}
}
func f64(x, y, q, r int64) {
if t := x / y; t != q {
fmt.Printf("%d/%d = %d, want %d\n", x, y, t, q)
}
if t := x % y; t != r {
fmt.Printf("%d%%%d = %d, want %d\n", x, y, t, r)
}
}
func main() {
f8(-1<<7, -1, -1<<7, 0)
f16(-1<<15, -1, -1<<15, 0)
f32(-1<<31, -1, -1<<31, 0)
f64(-1<<63, -1, -1<<63, 0)
}