[Bug tree-optimization/95433] Failure to completely optimize simple compare after operations
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95433 Andrew Pinski changed: What|Removed |Added Resolution|--- |FIXED Target Milestone|--- |11.0 Status|NEW |RESOLVED --- Comment #8 from Andrew Pinski --- Fixed in GCC 11 by the commits.
[Bug tree-optimization/95433] Failure to completely optimize simple compare after operations
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95433 --- Comment #7 from CVS Commits --- The master branch has been updated by Marc Glisse : https://gcc.gnu.org/g:287522613d661b4c5ba8403b051eb470c1674cba commit r11-2629-g287522613d661b4c5ba8403b051eb470c1674cba Author: Marc Glisse Date: Mon Aug 10 12:50:42 2020 +0200 Simplify X * C1 == C2 with wrapping overflow Odd numbers are invertible in Z / 2^n Z, so X * C1 == C2 can be rewritten as X == C2 * inv(C1) when overflow wraps. mod_inv should probably be updated to better match the other wide_int functions, but that's a separate issue. 2020-08-10 Marc Glisse PR tree-optimization/95433 * match.pd (X * C1 == C2): Handle wrapping overflow. * expr.c (maybe_optimize_mod_cmp): Qualify call to mod_inv. (mod_inv): Move... * wide-int.cc (mod_inv): ... here. * wide-int.h (mod_inv): Declare it. * gcc.dg/tree-ssa/pr95433-2.c: New file.
[Bug tree-optimization/95433] Failure to completely optimize simple compare after operations
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95433 --- Comment #6 from CVS Commits --- The master branch has been updated by Marc Glisse : https://gcc.gnu.org/g:ca2b8c082c4f16919071c9f8de8db0b33b54c405 commit r11-2550-gca2b8c082c4f16919071c9f8de8db0b33b54c405 Author: Marc Glisse Date: Tue Aug 4 17:30:16 2020 +0200 Simplify X * C1 == C2 with undefined overflow this transformation is quite straightforward, without overflow, 3*X==15 is the same as X==5 and 3*X==5 cannot happen. Adding a single_use restriction for the first case didn't seem necessary, although of course it can slightly increase register pressure in some cases. 2020-08-04 Marc Glisse PR tree-optimization/95433 * match.pd (X * C1 == C2): New transformation. * gcc.c-torture/execute/pr23135.c: Add -fwrapv to avoid undefined behavior. * gcc.dg/tree-ssa/pr95433.c: New file.
[Bug tree-optimization/95433] Failure to completely optimize simple compare after operations
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95433 --- Comment #5 from Marc Glisse --- Patch posted at https://gcc.gnu.org/pipermail/gcc-patches/2020-August/551154.html for the original testcase. Note that solving univariate polynomial equations *in the integers* (the rationals are not much harder) is actually rather simple, just enumerate the divisors of the constant term and evaluate the polynomial on each of them to check which ones are roots. If someone wants to implement that...
[Bug tree-optimization/95433] Failure to completely optimize simple compare after operations
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95433 Eric Botcazou changed: What|Removed |Added CC||ebotcazou at gcc dot gnu.org --- Comment #4 from Eric Botcazou --- > Hmm, are we supposed to solve/simplify arbitrary linear equations? > > 3 * x * x * x + 5 == 8 > > is equal to x == 1. > > 3 * x * x + 5 == 8 > > is equal to abs(x) == 1. Solving linear equations is at least tractable, which is not the case of general polynomial equations, especially if the degree is greater than 4. ;-)
[Bug tree-optimization/95433] Failure to completely optimize simple compare after operations
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95433 --- Comment #3 from joseph at codesourcery dot com --- This is of course only valid because signed overflow is undefined; it wouldn't be a valid optimization with -fwrapv (unless x were narrower than int so no overflow could occur).
[Bug tree-optimization/95433] Failure to completely optimize simple compare after operations
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95433 --- Comment #2 from Richard Biener --- Hmm, are we supposed to solve/simplify arbitrary linear equations? 3 * x * x * x + 5 == 8 is equal to x == 1. 3 * x * x + 5 == 8 is equal to abs(x) == 1. But sure, simple cases. I wonder if something more "general" can be done by reassoc rather than dealing with this in pattern matching.
[Bug tree-optimization/95433] Failure to completely optimize simple compare after operations
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95433 Marc Glisse changed: What|Removed |Added Ever confirmed|0 |1 Status|UNCONFIRMED |NEW Last reconfirmed||2020-05-30 --- Comment #1 from Marc Glisse --- It is 2*x==-2 that we fail to simplify. match.pd has code for x*2==y*2 or x*2==0 or even x*2.==-2. for floats, but apparently not for the special case of other constants for integers.
