Summary:
We should never outline the first basic block.
Also add an option to accept a file with the list of
functions to optimize.
(cherry picked from FBD2868184)
Summary:
We could split functions with exceptions even without creating
a new exception handling table. This limits us to only move
basic blocks that never throw, and are not a start of a
landing pad.
(cherry picked from FBD2862937)
Summary:
After basic block reordering, it may be possible that the reordered
function is now larger than the original because of the following reasons:
- jump offsets may change, forcing some jump instructions to use 4-byte
immediate operand instead of the 1-byte, shorter version.
- fall-throughs change, forcing us to emit an extra jump instruction to jump
to the original fall-through at the end of a basic block.
Since we currently do not change function addresses, we need to rewrite the
function back in the binary in the original location. If it doesn't fit, we were
dropping the function.
This patch adds a flag -split-functions that tells llvm-flo to split hot
functions into hot and cold separate regions. The hot region is written back
in the original function location, while the cold region is written in a
separate, far-away region reserved to flo via a linker script.
This patch also adds the logic to create and extra FDE to supply unwinding
information to the cold part of the function. Owing to this, we now need to
rewrite .eh_frame_hdr to another location and patch the EH_FRAME ELF segment
to point to this new .eh_frame_hdr.
(cherry picked from FBD2677996)
Summary:
This patch introduces logic to check how the CFI instructions define a
table to help during stack unwinding at exception run time and attempts to fix
any problem in this table that may have been introduced by reordering the basic
blocks. If it fails to fix this problem, the function is marked as not simple
and not eligible for rewriting.
(cherry picked from FBD2633696)
Summary:
Pettis' paper on block layout (PLDI'90) suggests we should order
clusters (or chains, using the paper terminology) using a specific criterion.
This patch implements two distinct ideas for cluster layout that can be
activated using different command-line flags. The first one reflects Pettis'
ideas on minimizing branch mispredictions and the second one is targeted at
reducing I-cache misses, described in the Ispike paper (CGO'04).
(cherry picked from FBD2588693)
Summary:
Nop instructions are primarily used for alignment purposes on the input.
We remove all nops when we build CFG and derive alignment of basic blocks
based on existing alignment and a presence of nops before it. This
will not always work as some basic blocks will be naturally aligned
without necessity for nops. However, it's better than random alignment.
We would also add heuristics for BB alignment based on execution profile.
(cherry picked from FBD2561740)
Summary:
Adds logic in BinaryFunction to be able to fix branches (invert
its condition, delete or add a branch), making the new function work with the
new layout proposed by the layout pass. All the architecture-specific content
was designed to live in the LLVM Target library, in the MCInstrAnalysis pass.
For now, we only introduce such logic to the X86 backend.
(cherry picked from FBD2551479)
Summary:
The LBR only has information about taken branches and does not record
information when a branch is not taken. In our CFG, we call these edges
"fall-through" edges. This patch teaches llvm-flo how to infer fall-through
edge frequencies.
(cherry picked from FBD2536633)
