http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52876
Bug #: 52876
Summary: [x32] - Sign extend 32 to 64bit then clear upper
32bits fails O1 or higher
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: steffen-schm...@siemens.com
Created attachment 27096
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27096
Example code v1
This function sign extends an x32 32bit void* into a 64bit long long global
variable. Afterwards it zeros upper 32bits using binary AND.
long long li;
long long testfunc(void* addr) __attribute__ ((noinline));
long long testfunc(void* addr)
{
li = (long long)(int)addr;
// next line is important, if the address from pv
// has been sign extended with leading ONEs
li &= 0xffffffff;
return li;
}
int main (void)
{
volatile long long rv_test;
rv_test = testfunc((void*)0x87651234);
return 0;
}
The following examples are called with parameter (void*)0x87651234
Compiled with gcc 4.7.0 -mx32 -O0 produces:
movq %rdi, %rax
movl %eax, -4(%rbp)
movl -4(%rbp), %eax
cltq #sign extend EAX to RAX, e.g. 0x87651234 to 0xffffffff87651234
movq %rax, li(%rip)
movq li(%rip), %rax
andl $4294967295, %eax #the AND 0xffffffff, producing 0x0000000087651234
movq %rax, li(%rip)
movq li(%rip), %rax
Compiled with gcc 4.7.0 -mx32 -O1 produces:
movslq %edi, %rax #this is only a sign extend producing 0xffffffff87651234
#the zero-ing of the upper 32bits is missing.
movq %rax, li(%rip)
Compiled with gcc 4.6.3 (x32 branch) -mx32 -O1 produces:
movq %rdi, %rax #Here the sign extend and the AND are combined to a mov
#the results in 0x0000000087651234 which is correct.
movq %rdi, li(%rip)
It seems that somehow gcc 4.7.0 "forgets" to clear the upper bits, which gcc
4.6.3 branch x32 did correctly.
The effect only happens in a stand-alone function and using a global variable,
when inlining, the result is correct.
I've attached 3 versions of the test, all failing in O1 or higher. The first
using a global variable, the second a union and a local variable, the third
using a variadic function.
