[Bug target/108004] x-form logical operations with dot instructions are not emitted.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108004 Segher Boessenkool changed: What|Removed |Added Ever confirmed|0 |1 Resolution|INVALID |--- Status|RESOLVED|SUSPENDED Last reconfirmed||2023-01-09 --- Comment #7 from Segher Boessenkool --- It's not really invalid, but it won't happen any time soon. The upper bits *are* defined for argument passing, in all our 64-bit ABIs: for signed type (like here the value is passed sign-extended. But the code has "(a & b) > 0" which does the comparison as an int. In combine we get Trying 11 -> 14: 11: r124:SI=r129:DI#4:DI#4 REG_DEAD r130:DI REG_DEAD r129:DI 14: r125:CC=cmp(r124:SI,0) REG_DEAD r124:SI Failed to match this instruction: (set (reg:CC 125) (compare:CC (and:SI (subreg:SI (reg:DI 129) 4) (subreg:SI (reg:DI 130) 4)) (const_int 0 [0]))) If we upgraded some stuff to DImode instead of SImode, sometimes we can make better code, like we could here. But in other cases the opposite is true. I think it is likely it helps more often than it would hurt, and we can upgrade the mode only sometimes as well of course. In any case, this is just a special case of a much more generic problem (in all ports, not just rs6000!), that has been known for a very long time, and no real progress has been made yet. But it definitely should be doable. To simplify the problem a lot it probably is okay to only consider upgrading the mode of a pseudo everywhere (so not do it in some insns but not others), and then assign a score to it. Probably a higher score inside loops, that is the case where we see this most / where we see it as a shortcoming most. Where rs6000 is special here is that we have "w" and "d" (32-bit and 64-bit) variants of many insns (but no smaller versions most of the time fwiw).
[Bug target/108004] x-form logical operations with dot instructions are not emitted.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108004 Andrew Pinski changed: What|Removed |Added Resolution|--- |INVALID Status|UNCONFIRMED |RESOLVED --- Comment #6 from Andrew Pinski --- Using long instead of int gives: and. 4,3,4 isel 3,5,6,1 blr Which is what you want there. and. is incorrect for int as the upper bits are not defined for argument passing ...
[Bug target/108004] x-form logical operations with dot instructions are not emitted.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108004 Segher Boessenkool changed: What|Removed |Added CC||segher at gcc dot gnu.org --- Comment #5 from Segher Boessenkool --- (In reply to HaoChen Gui from comment #0) > and 3,3,4 > cmpwi 0,3,0 > isel 5,5,6,1 > extsw 3,5 > > The "and" and "cmpwi" can be optimized to "and." instruction. The same as > "or" and "xor". It cannot be "and.", that would do "cmpdi 3,0", and we want "cmpwi" here.
[Bug target/108004] x-form logical operations with dot instructions are not emitted.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108004
--- Comment #4 from HaoChen Gui ---
$cat asm_test.c
#include
unsigned long foo() {
unsigned long res;
__asm__ ("li 3,0x\n\t"
"li 4,0xfff1\n\t"
"and. 3,3,4\n\t"
"mfcr %0"
: "=r" (res));
return res;
}
void
main()
{
printf ("%lx\n", foo());
}
$ gcc -O1 -o asm_test asm_test.c && ./asm_test
82000482
Use the assembly to test the "and.". The bit32 (cr0 LT bit) is set when the
result is less than 0.
[Bug target/108004] x-form logical operations with dot instructions are not emitted.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108004 --- Comment #3 from HaoChen Gui --- (In reply to Andrew Pinski from comment #2) > Especially when it comes to signed comparisons. >From the ISA, For all fixed-point instructions in which Rc=1, and for addic., andi., and andis., the first three bits of CR Field 0 (bits 32:34 of the Condition Register) are set by signed comparison of the result to zero, and the fourth bit of CR Field 0 (bit 35 of the Condition Register) is copied from the SO field of the XER.
[Bug target/108004] x-form logical operations with dot instructions are not emitted.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108004 --- Comment #2 from Andrew Pinski --- Especially when it comes to signed comparisons.
[Bug target/108004] x-form logical operations with dot instructions are not emitted.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108004 --- Comment #1 from Andrew Pinski --- >From what I remember and. Only sets eq bit correctly.
