Bug 8796 – Optimizer bug on 64bit: *p++=1 where p is a parameter
Status
RESOLVED
Resolution
FIXED
Severity
critical
Priority
P2
Component
dmd
Product
D
Version
D2
Platform
All
OS
All
Creation time
2012-10-10T14:13:00Z
Last change time
2015-06-09T05:11:59Z
Keywords
wrong-code
Assigned to
nobody
Creator
dmitry.olsh
Comments
Comment #0 by dmitry.olsh — 2012-10-10T14:13:18Z
Uncovered while doing a re-write for std.array.insertInPlace.
It got caught by pull auto-tester.
Sample:
import std.conv, std.utf;
void insertInPlace(T, U...)(ref T[] array, size_t pos, U stuff)
{
{// mutable, can do in place
//helper function: re-encode dchar to Ts and store at *ptr
static T* putDChar(T* ptr, dchar ch)
{
static if(is(T == dchar))
{
*ptr++ = ch;
return ptr;
}
else
{
T[dchar.sizeof/T.sizeof] buf;
size_t len = encode(buf, ch);
final switch(len)
{
static if(T.sizeof == char.sizeof)
{
case 4:
ptr[3] = buf[3];
goto case;
case 3:
ptr[2] = buf[2];
goto case;
}
case 2:
ptr[1] = buf[1];
goto case;
case 1:
ptr[0] = buf[0];
}
ptr += len;
return ptr;
}
}
immutable oldLen = array.length;
size_t to_insert = 0;
foreach (i, E; U)
to_insert += codeLength!T(stuff[i]);
array.length += to_insert;
auto ptr = array.ptr + pos;
foreach (i, E; U)
{
static if(is(E : dchar))
{
ptr = putDChar(ptr, stuff[i]);
}
else
{
foreach (dchar ch; stuff[i])
ptr = putDChar(ptr, ch);
}
}
assert(ptr == array.ptr + pos + to_insert, text(ptr - array.ptr, " vs ",pos+ to_insert ));
}
}
void main()
{
auto l = "hello"d.dup;
auto r = " વિશ્વ".dup;
l.insertInPlace(0, r);
}
Compiled as
dmd -O atest.d
It fails with:
[email protected](75): 0 vs 6
Compiled without -O it doesn't fail. It also works fine in 32 bits.
Tested with dmd 2.061 from github. Commit a1287bd0b1931917f4e43b5e2d7b997f0d60adf6.
Comment #1 by clugdbug — 2012-11-05T11:43:22Z
Reduced test case (applies to postfix ++ and --):
int* wrong8796(int* p)
{
*p++ = 1;
return p;
}
// The wrong code is generated in the function above, main() is just to demonstrate
void main()
{
int [3] arr;
int * q = arr.ptr;
q = wrong8796(q);
assert(q != arr.ptr);
}
Without -O, wrong8796() compiles to:
push RBP
mov RBP,RSP
sub RSP,8
mov -8[RBP],RDI
mov RAX,-8[RBP]
add qword ptr -8[RBP],4
mov dword ptr [RAX],1
mov RAX,-8[RBP]
leave
ret
With -O:
push RBP
mov RBP,RSP
mov RAX,RDI
mov qword ptr [RAX],1
add RAX,4
mov RAX,RDI <---- wrong
pop RBP
ret
Comment #2 by github-bugzilla — 2012-12-10T23:45:40Z