The existing way of creating the predicate in the guard blocks uses
a boolean value per outgoing block. This increases the number of live
booleans as the number of outgoing blocks increases. The new way added
in this change is to store one integer to represent the outgoing block
we want to branch to, then at each guard block, an integer equality
check is performed to decide which a specific outgoing block is taken.
Using an integer reduces the number of live values and decreases
register pressure especially in cases where there are a large number
of outgoing blocks. The integer based approach is used when the
number of outgoing blocks crosses a threshold, which is currently set
to 32.
Patch by Ruiling Song.
Differential review: https://reviews.llvm.org/D127831
The NewDefault was used to simplify the updating of PHI nodes, but it
causes some inefficiency for target that will run structurizer later. For
example, for a simple two-case switch, the extra NewDefault is causing
unstructured CFG like:
O
/ \
O O
/ \ / \
C1 ND C2
\ | /
\ | /
D
The change is to avoid the ND(NewDefault) block, that is we will get a
structured CFG for above example like:
O
/ \
/ \
O O
/ \ / \
C1 \ / C2
\-> D <-/
The IR change introduced by this patch should be trivial to other targets,
so I am doing this unconditionally.
Fall-through among the cases will also cause unstructured CFG, but it need
more work and will be addressed in a separate change.
Reviewed by: arsenm
Differential Revision: https://reviews.llvm.org/D123607
In the NPM, a pass cannot depend on another non-analysis pass. So pin
the test that tests that -lowerswitch is run automatically to legacy PM.
Reviewed By: sameerds
Differential Revision: https://reviews.llvm.org/D89051
Summary:
- Skip unreachable predecessors during header detection in SCC. Those
unreachable blocks would be generated in the switch lowering pass in
the corner cases or other frontends. Even though they could be removed
through the CFG simplification, we should skip them during header
detection.
Reviewers: sameerds
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D83562
Summary:
When an irreducible SCC is converted into a new natural loop, existing
loops included in that SCC now become children of the new loop. The
logic that moves these loops from the parent loop to the new loop
invoked undefined behaviour when it modified the container that it was
iterating over. Fixed this by first extracting all the loops that are
to be removed from the parent.
Fixes bug 45623.
Reviewed By: arsenm
Differential Revision: https://reviews.llvm.org/D78544
An irreducible SCC is one which has multiple "header" blocks, i.e., blocks
with control-flow edges incident from outside the SCC. This pass converts an
irreducible SCC into a natural loop by introducing a single new header
block and redirecting all the edges on the original headers to this
new block.
This is a useful workaround for a limitation in the structurizer
which, which produces incorrect control flow in the presence of
irreducible regions. The AMDGPU backend provides an option to
enable this pass before the structurizer, which may eventually be
enabled by default.
Reviewed By: nhaehnle
Differential Revision: https://reviews.llvm.org/D77198
This restores commit 2ada8e2525dd2653f30c8696a27162a3b1647d66.
Originally reverted with commit 44e09b59b869a91bf47d76e8bc569d9ee91ad145.
This reverts commit 2ada8e2525dd2653f30c8696a27162a3b1647d66.
Buildbots produced compilation errors which I was not able to quickly
reproduce locally. Need more time to investigate.
An irreducible SCC is one which has multiple "header" blocks, i.e., blocks
with control-flow edges incident from outside the SCC. This pass converts an
irreducible SCC into a natural loop by introducing a single new header
block and redirecting all the edges on the original headers to this
new block.
This is a useful workaround for a limitation in the structurizer
which, which produces incorrect control flow in the presence of
irreducible regions. The AMDGPU backend provides an option to
enable this pass before the structurizer, which may eventually be
enabled by default.
Reviewed By: nhaehnle
Differential Revision: https://reviews.llvm.org/D77198
