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4 Commits

Author SHA1 Message Date
Simon Pilgrim
ffe13960b5 [InstCombine] Fold (A & 2^C1) + A => A & (2^C1 - 1) iff bit C1 in A is a sign bit (PR21929) 
Alive2: https://alive2.llvm.org/ce/z/Ygq26C

This is the final missing fold to handle the modulo2 simplification: https://github.com/llvm/llvm-project/issues/22303

Fixes #22303

Differential Revision: https://reviews.llvm.org/D123374
 2022-04-22 16:59:02 +01:00
Simon Pilgrim
5b45c0b677 [InstCombine] Add various other modulo-by-constant tests for Issue #22303 2022-04-08 10:37:13 +01:00
Simon Pilgrim
5e90224839 [InstCombine] SimplifyDemandedUseBits - remove lshr node if we only demand known sign bit 
This is a lshr equivalent to D122340 - if we don't demand any of the additional sign bits introduced by the ashr, the lshr can be treated as an ashr and we can remove the shift entirely if we only demand already known sign bits.

Another step towards PR21929

https://alive2.llvm.org/ce/z/6f3kjq

Differential Revision: https://reviews.llvm.org/D123118
 2022-04-07 14:33:31 +01:00
Simon Pilgrim
cd47be0c3b [InstCombine] Add PR22303 test case 2022-04-05 11:12:23 +01:00