Summary:
Converting outermost zext(a) to sext(a) causes worse code when the
computation of zext(a) could be reused. For example, after converting
... = array[zext(a)]
... = array[zext(a) + 1]
to
... = array[sext(a)]
... = array[zext(a) + 1],
the program computes sext(a), which is actually unnecessary. I added one
test in split-gep-and-gvn.ll to illustrate this scenario.
Also, with r211281 and r211084, we annotate more "nuw" tags to
computation involving CUDA intrinsics such as threadIdx.x. These
annotations help with splitting GEP a lot, rendering the benefit we get
from this reverted optimization only marginal.
Test Plan: make check-all
Reviewers: eliben, meheff
Reviewed By: meheff
Subscribers: jholewinski, llvm-commits
Differential Revision: http://reviews.llvm.org/D4542
llvm-svn: 213209
For each array index that is in the form of zext(a), convert it to sext(a)
if we can prove zext(a) <= max signed value of typeof(a). The conversion
helps to split zext(x + y) into sext(x) + sext(y).
Reviewed in http://reviews.llvm.org/D4060
llvm-svn: 210444
Most issues are on mishandling s/zext.
Fixes:
1. When rebuilding new indices, s/zext should be distributed to
sub-expressions. e.g., sext(a +nsw (b +nsw 5)) = sext(a) + sext(b) + 5 but not
sext(a + b) + 5. This also affects the logic of recursively looking for a
constant offset, we need to include s/zext into the context of the searching.
2. Function find should return the bitwidth of the constant offset instead of
always sign-extending it to i64.
3. Stop shortcutting zext'ed GEP indices. LLVM conceptually sign-extends GEP
indices to pointer-size before computing the address. Therefore, gep base,
zext(a + b) != gep base, a + b
Improvements:
1. Add an optimization for splitting sext(a + b): if a + b is proven
non-negative (e.g., used as an index of an inbound GEP) and one of a, b is
non-negative, sext(a + b) = sext(a) + sext(b)
2. Function Distributable checks whether both sext and zext can be distributed
to operands of a binary operator. This helps us split zext(sext(a + b)) to
zext(sext(a) + zext(sext(b)) when a + b does not signed or unsigned overflow.
Refactoring:
Merge some common logic of handling add/sub/or in find.
Testing:
Add many tests in split-gep.ll and split-gep-and-gvn.ll to verify the changes
we made.
llvm-svn: 210291
This is an enhancement to SeparateConstOffsetFromGEP. With this patch, we can
extract a constant offset from "s/zext and/or/xor A, B".
Added a new test @ext_or to verify this enhancement.
Refactoring the code, I also extracted some common logic to function
Distributable.
llvm-svn: 209670
Fixed a TODO in r207783.
Add the extracted constant offset using GEP instead of ugly
ptrtoint+add+inttoptr. Using GEP simplifies future optimizations and makes IR
easier to understand.
Updated all affected tests, and added a new test in split-gep.ll to cover a
corner case where emitting uglygep is necessary.
llvm-svn: 209537
This optimization merges the common part of a group of GEPs, so we can compute
each pointer address by adding a simple offset to the common part.
The optimization is currently only enabled for the NVPTX backend, where it has
a large payoff on some benchmarks.
Review: http://reviews.llvm.org/D3462
Patch by Jingyue Wu.
llvm-svn: 207783
Jingyue Wu