On 9/5/24 12:38 PM, Raphael Zinsly wrote:
On Thu, Sep 5, 2024 at 3:10 PM Jeff Law <jeffreya...@gmail.com> wrote:
On 9/5/24 6:16 AM, Raphael Zinsly wrote:
On Wed, Sep 4, 2024 at 8:32 PM Jeff Law <j...@ventanamicro.com> wrote:
On 9/2/24 2:01 PM, Raphael Moreira Zinsly wrote:
...
+ bool bit31 = (hival & 0x80000000) != 0;
+ int trailing_shift = ctz_hwi (loval) - ctz_hwi (hival);
+ int leading_shift = clz_hwi (loval) - clz_hwi (hival);
+ int shiftval = 0;
+
+ /* Adjust the shift into the high half accordingly. */
+ if ((trailing_shift > 0 && hival == (loval >> trailing_shift))
+ || (trailing_shift < 0 && hival == (loval << trailing_shift)))
+ shiftval = 32 - trailing_shift;
+ else if ((leading_shift < 0 && hival == (loval >> leading_shift))
+ || (leading_shift > 0 && hival == (loval << leading_shift)))
Don't these trigger undefined behavior when tailing_shift or
leading_shift is < 0? We shouldn't ever generate negative shift counts.
The value of trailing/leading_shift is added to 32, we will never have
negative shift counts.
In the IF you have this conditional:
(trailing_shift < 0 && hival == (loval << trailing_shift))
How could that not be undefined behvaior? You first test that the value
is less than zero and if it is less than zero you use it as a shift count.
I'm not using trailing_shift as the shift count, I'm using shiftval:
+ /* Now we want to shift the previously generated constant into the
+ high half. */
+ alt_codes[alt_cost - 2].code = ASHIFT;
+ alt_codes[alt_cost - 2].value = shiftval;
+ alt_codes[alt_cost - 2].use_uw = false;
+ alt_codes[alt_cost - 2].save_temporary = false;
I'm not referring to the generated code. The compiler itself will
exhibit undefined behavior due to the negative shift count in that test.
jeff
