[Bug tree-optimization/102648] [12 Regression] Dead Code Elimination Regression at -O3 (trunk vs 11.2.0) since r12-2381-g704e8a825c78b9a8
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102648 Andrew Macleod changed: What|Removed |Added Status|NEW |RESOLVED Resolution|--- |FIXED --- Comment #4 from Andrew Macleod --- Should be fixed.
[Bug tree-optimization/102648] [12 Regression] Dead Code Elimination Regression at -O3 (trunk vs 11.2.0) since r12-2381-g704e8a825c78b9a8
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102648 --- Comment #3 from CVS Commits --- The master branch has been updated by Andrew Macleod : https://gcc.gnu.org/g:1598bd47b2a4a5f12b5a987d16d82634644db4b6 commit r12-5524-g1598bd47b2a4a5f12b5a987d16d82634644db4b6 Author: Andrew MacLeod Date: Thu Nov 25 08:58:19 2021 -0500 Add the testcase for this PR to the testsuite. Various ranger-enabled patches like threading and VRP2 can do this now, so add the testcase for posterity. gcc/testsuite/ PR tree-optimization/102648 * gcc.dg/pr102648.c: New.
[Bug tree-optimization/102648] [12 Regression] Dead Code Elimination Regression at -O3 (trunk vs 11.2.0) since r12-2381-g704e8a825c78b9a8
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102648 --- Comment #2 from Andrew Macleod --- This is another case of insufficient range representation in the old value_range. The patch causing the issue allows us to produce better subranges when the source ranges have small numbers of constants in them. We have the sequence: g.8_18 = (unsigned short) _2; _19 = g.8_18 * 4; _20 = (short int) _19; if (_20 > 1) we calculate that g.8_18 has a range of [0,1] before this patch, we calculated: _19 = unsigned short ~[1, 3] _20 = short int [-25536, 0] if (_20 > 1) could then be folded as never taken. With the precision change, we calculate _19 as [0,0][4,4], which when converted to a value range, becomes [0,4]. This then causes _20 be calculated as short int ~[-25535, -1] which can no longer correctly predict that the branch can never be taken. This problem goes away if we run another evrp instance later instead of VRP as this is a non issue with multi-ranges as we get: g.8_18 : unsigned short [0, 1] _19 : unsigned short [0, 0][4, 4] _20 : short int [-25536, -25536][0, 0] and can easily fold away the condition.
[Bug tree-optimization/102648] [12 Regression] Dead Code Elimination Regression at -O3 (trunk vs 11.2.0) since r12-2381-g704e8a825c78b9a8
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102648 Martin Liška changed: What|Removed |Added CC||marxin at gcc dot gnu.org Status|UNCONFIRMED |NEW Summary|[12 Regression] Dead Code |[12 Regression] Dead Code |Elimination Regression at |Elimination Regression at |-O3 (trunk vs 11.2.0) |-O3 (trunk vs 11.2.0) since ||r12-2381-g704e8a825c78b9a8 Ever confirmed|0 |1 Last reconfirmed||2021-10-11 --- Comment #1 from Martin Liška --- Started with r12-2381-g704e8a825c78b9a8.
