[Bug tree-optimization/102738] Failure to optimize (signed) right shift if the range is already known to be [-1, 0]
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102738 Andrew Pinski changed: What|Removed |Added Summary|Failure to optimize right |Failure to optimize |shift of 32-bit int after |(signed) right shift if the |it's already been shifted |range is already known to |by 31 |be [-1, 0] Severity|normal |enhancement
[Bug tree-optimization/102738] Failure to optimize (signed) right shift if the range is already known to be [-1, 0]
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102738
--- Comment #2 from Andrew Pinski ---
So this is interesting, I think clang/LLVM does this optimization late in their
pipeline take:
int a1(int f, int g)
{
if (f == 0 || f == 1)
return (f-1) >> g;
return 0;
}
They don't remove the shift at all. But if you change return 0 to
__builtin_unreachable(), they remove the shift.
Anyways we should be able to do this optimization even in the above case.
And even here where clang/LLVM misses too:
int a1(int f, int g)
{
if (f == 6 || f == 7)
return (f-7) >> g;
__builtin_unreachable();
}
[Bug tree-optimization/102738] Failure to optimize (signed) right shift if the range is already known to be [-1, 0]
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102738 --- Comment #3 from CVS Commits --- The master branch has been updated by Andrew Macleod : https://gcc.gnu.org/g:f0b7d4cc49ddb1c2c7474cc3f61e260aa93a96c0 commit r12-4413-gf0b7d4cc49ddb1c2c7474cc3f61e260aa93a96c0 Author: Andrew MacLeod Date: Thu Oct 14 10:43:58 2021 -0400 Simplification for right shift. When the first operand of a signed right shift is zero or negative one, the RHS doesn't matter and the shift can be converted to a copy. PR tree-optimization/102738 gcc/ * vr-values.c (simplify_using_ranges::simplify): Handle RSHIFT_EXPR. gcc/testsuite * gcc.dg/pr102738.c: New.
[Bug tree-optimization/102738] Failure to optimize (signed) right shift if the range is already known to be [-1, 0]
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102738 Andrew Macleod changed: What|Removed |Added CC||amacleod at redhat dot com Resolution|--- |FIXED Status|NEW |RESOLVED --- Comment #4 from Andrew Macleod --- I added this to the simplifier, so we now get all these cases right in EVRP. I incorporated all 6 into one test.
