[PATCH] D26000: [InstCombine] Folding of shifts by the sum of positive values

[Simon Pilgrim via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: majnemer, nadav, spatel, filcab, andreadb.
RKSimon added subscribers: llvm-commits, nadav.
RKSimon set the repository for this revision to rL LLVM.

This patch introduces the combine:

(C1 shift (A add C2)) -> ((C1 shift C2) shift A)
iff A and C2 are both positive

If both A and C2 are know to be positive then we can safely split into 2 shifts, permitting the folding of the Inner shift.

Fix for the spec benchmark case mentioned by @nadav on PR15141 (assuming we can prove that the inputs as positive).


Repository:
  rL LLVM

https://reviews.llvm.org/D26000

Files:
  lib/Transforms/InstCombine/InstCombineShifts.cpp
  test/Transforms/InstCombine/shift-add.ll

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