The low-overhead branch extension provides a loop-end 'LE' instruction
that performs no decrement nor compare, it just jumps backwards. This
patch modifies the constant islands pass to try to insert LE
instructions in place of a Thumb2 conditional branch, instead of
shrinking it. This only happens if a cmp can be converted to a cbn/z
and used to exit the loop.
Differential Revision: https://reviews.llvm.org/D67404
llvm-svn: 372085
rL369567 reverted a couple of recent changes made to ARMParallelDSP
because of a miscompilation error: PR43073.
The issue stemmed from an underlying bug that was caused by adding
muls into a reduction before it was proved that they could be executed
in parallel with another mul.
Most of the changes here are from the previously reverted commits.
The additional changes have been made area:
1) The Search function now doesn't insert any muls into the Reduction
object. That now happens once the search has successfully finished.
2) For any muls added into the reduction but that weren't paired, we
accumulate their values as an input into the smlad.
Differential Revision: https://reviews.llvm.org/D66660
llvm-svn: 370171
Summary:
Current PRE hoists common computations into
CMBB = DT->findNearestCommonDominator(MBB, MBB1).
However, if CMBB is in a hot loop body, we might get performance
degradation.
Differential Revision: https://reviews.llvm.org/D64394
llvm-svn: 366570
This allows later passes (in particular InstCombine) to optimize more
cases.
One that's important to us is `memcmp(p, q, constant) < 0` and memcmp(p, q, constant) > 0.
llvm-svn: 364412
Introduce three pseudo instructions to be used during DAG ISel to
represent v8.1-m low-overhead loops. One maps to set_loop_iterations
while loop_decrement_reg is lowered to two, so that we can separate
the decrement and branching operations. The pseudo instructions are
expanded pre-emission, where we can still decide whether we actually
want to generate a low-overhead loop, in a new pass:
ARMLowOverheadLoops. The pass currently bails, reverting to an sub,
icmp and br, in the cases where a call or stack spill/restore happens
between the decrement and branching instructions, or if the loop is
too large.
Differential Revision: https://reviews.llvm.org/D63476
llvm-svn: 364288
This allows targets to make more decisions about reserved registers
after isel. For example, now it should be certain there are calls or
stack objects in the frame or not, which could have been introduced by
legalization.
Patch by Matthias Braun
llvm-svn: 363757
Initial commit of a new pass to create vector predication blocks, called VPT
blocks, that are supported by the Armv8.1-M MVE architecture.
This is a first naive implementation. I.e., for 2 consecutive predicated
instructions I1 and I2, for example, it will generate 2 VPT blocks:
VPST
I1
VPST
I2
A more optimal implementation would obviously put instructions in the same VPT
block when they are predicated on the same condition and when it is allowed to
do this:
VPTT
I1
I2
We will address this optimisation with follow up patches when the groundwork is
in. Creating VPT Blocks is very similar to IT Blocks, which is the reason I
added this to Thumb2ITBlocks.cpp. This allows reuse of the def use analysis
that we need for the more optimal implementation.
VPT blocks cannot be nested in IT blocks, and vice versa, and so these 2 passes
cannot interact with each other. Instructions allowed in VPT blocks must
be MVE instructions that are marked as VPT compatible.
Differential Revision: https://reviews.llvm.org/D63247
llvm-svn: 363370
Sam Parker