Hello, all Can gatekeeper review the patch to bug #544 for me please? Thank you.
Bug #544 is caused by bitwise dead code elimniation (BDCE) in WOPT. It
happens with -m32 -O2 (or -O3 but not -O0). The test case looks like
follows:
int sy(unsigned long a)
{
unsigned long j4;
long tmp;
j4=a+(a&0x5555555555555555)>>0x1;
return j4&0x44;
}
Before BDCE, the expression a&0x5555555555555555 is converted into:
> LDID U8 U8 sym5v2 50 ty=502 <u=2 cr17> flags:0x0 b=-1
> LDC I8 6148914691236517205 <u=0 cr5> flags:0x0 b=-1
> I8BAND <u=1 cr18> isop_flags:0xc0040 flags:0x1 b=E1
Now, the expression j4&0x44 causes BDCE to mark only the 2nd and 6th
bit being live for j4. Going backward,
j4=(a+a&0x5555555555555555)>>0x1 causes BDCE think only the first byte
of a&0x5555555555555555 is live. Based on this information, BDCE think
we can use converted the I8BAND (with both operand type and result
type being 64-bit long) to I4BAND (with both operand type and result
type being 32-bit long). However, in this case, both of the result
type of I8BAND's children can not be shortened to 32-bit long. So, we
can not do this I8BAND -> I4BAND transformation in this case.
-- Feng
bug544.patch
Description: Binary data
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