On 10/8/20 4:39 PM, Jakub Jelinek wrote:
On Thu, Oct 08, 2020 at 04:28:37PM +0200, Aldy Hernandez wrote:
On 10/8/20 3:54 PM, Jakub Jelinek wrote:
On Thu, Oct 08, 2020 at 12:22:11PM +0200, Jakub Jelinek via Gcc-patches wrote:
Perhaps another way out of this would be document and enforce that
__builtin_c[lt]z{,l,ll} etc calls are undefined at zero, but C[TL]Z ifn
calls are defined there based on *_DEFINED_VALUE_AT_ZERO (*) == 2
Huh, that magic 2 is not obvious. I guess we should document the values of
this macro in the source somewhere:
The 2 is documented in gccint documentation.
BTW. There's no reason why the vr-values can't just call the
gimple_ranger::range_of_builtin_call. In the original implementation we had
vr-values call the ranger version and trap if they differed. I'm pretty
sure you can have vr-values call range_of_builtin_call with a value_range,
and things will get squashed down appropriately. We should really only have
one version of this. I'm not suggesting you do it, but I wouldn't object to
it ;-).
Will defer that to you or Andrew ;).
I can do it once the dust settles.
--- gcc/gimple-range.cc.jj 2020-10-08 11:55:25.498313173 +0200
+++ gcc/gimple-range.cc 2020-10-08 15:36:14.926945183 +0200
@@ -714,8 +730,14 @@ gimple_ranger::range_of_builtin_call (ir
// the maximum.
wide_int max = r.upper_bound ();
if (max == 0)
- break;
- maxi = wi::floor_log2 (max);
+ {
+ if (mini == -1)
+ maxi = -1;
+ else if (maxi == prec)
+ mini = prec;
+ }
+ else if (maxi != prec)
+ maxi = wi::floor_log2 (max);
Hmmm, if max == 0, that means the range is [0, 0], because if the highest
bound of r is 0, there's nothing left on the bottom but another 0 since R is
unsigned. Is that what you meant?
Yes, for max == 0 aka [0, 0] I wanted:
1) if mini == -1, i.e. the DEFINED_VALUE_AT_ZERO == 2 VALUE is -1, return [-1,
-1]
2) if maxi == prec, i.e. DEFINED_VALUE_AT_ZERO == 2 VALUE is prec, return
[prec, prec]
Ah, I see. Do you mind commenting that? Or perhaps you could spell it
out obviously like:
if (max == 0) {
...
if (DEFINED_VALUE_AT_ZERO)
// do special things
...
}
But whatever is fine. I hope to never look at these bits ever again :).
Aldy
