Commit Graph

23 Commits

Author SHA1 Message Date
Paul Robinson be179b9946 [FastISel] NFC: Remove obsolete -fast-isel-sink-local-values option
This option is not used for anything after #c161665 (D91737).
This commit reapplies #a474657.
2021-01-11 09:32:49 -08:00
David Blaikie 615f63e149 Revert "[FastISel] Flush local value map on ever instruction" and dependent patches
This reverts commit cf1c774d6a.

This change caused several regressions in the gdb test suite - at least
a sample of which was due to line zero instructions making breakpoints
un-lined. I think they're worth investigating/understanding more (&
possibly addressing) before moving forward with this change.

Revert "[FastISel] NFC: Clean up unnecessary bookkeeping"
This reverts commit 3fd39d3694.

Revert "[FastISel] NFC: Remove obsolete -fast-isel-sink-local-values option"
This reverts commit a474657e30.

Revert "Remove static function unused after cf1c774."
This reverts commit dc35368ccf.

Revert "[lldb] Fix TestThreadStepOut.py after "Flush local value map on every instruction""
This reverts commit 53a14a47ee.
2020-12-01 14:26:23 -08:00
Paul Robinson a474657e30 [FastISel] NFC: Remove obsolete -fast-isel-sink-local-values option
This option is not used for anything after #dc35368 (D91734).
2020-11-30 10:55:49 -08:00
Matt Arsenault 89baeaef2f Reapply "RegAllocFast: Rewrite and improve"
This reverts commit 73a6a164b8.
2020-09-30 10:35:25 -04:00
Muhammad Omair Javaid 73a6a164b8 Revert "Reapply Revert "RegAllocFast: Rewrite and improve""
This reverts commit 55f9f87da2.

Breaks following buildbots:
http://lab.llvm.org:8011/builders/lldb-arm-ubuntu/builds/4306
http://lab.llvm.org:8011/builders/lldb-aarch64-ubuntu/builds/9154
2020-09-22 14:40:06 +05:00
Matt Arsenault 55f9f87da2 Reapply Revert "RegAllocFast: Rewrite and improve"
This reverts commit dbd53a1f0c.

Needed lldb test updates
2020-09-21 15:45:27 -04:00
Eric Christopher dbd53a1f0c Temporarily Revert "RegAllocFast: Rewrite and improve"
as it's breaking a few tests in the lldb test suite.

Bot: http://lab.llvm.org:8011/builders/lldb-arm-ubuntu/builds/4226/steps/test/logs/stdio

This reverts commit c8757ff3aa.
2020-09-18 18:11:21 -07:00
Matt Arsenault c8757ff3aa RegAllocFast: Rewrite and improve
This rewrites big parts of the fast register allocator. The basic
strategy of doing block-local allocation hasn't changed but I tweaked
several details:

Track register state on register units instead of physical
registers. This simplifies and speeds up handling of register aliases.
Process basic blocks in reverse order: Definitions are known to end
register livetimes when walking backwards (contrary when walking
forward then uses may or may not be a kill so we need heuristics).

Check register mask operands (calls) instead of conservatively
assuming everything is clobbered.  Enhance heuristics to detect
killing uses: In case of a small number of defs/uses check if they are
all in the same basic block and if so the last one is a killing use.
Enhance heuristic for copy-coalescing through hinting: We check the
first k defs of a register for COPYs rather than relying on there just
being a single definition.  When testing this on the full llvm
test-suite including SPEC externals I measured:

average 5.1% reduction in code size for X86, 4.9% reduction in code on
aarch64. (ranging between 0% and 20% depending on the test) 0.5%
faster compiletime (some analysis suggests the pass is slightly slower
than before, but we more than make up for it because later passes are
faster with the reduced instruction count)

Also adds a few testcases that were broken without this patch, in
particular bug 47278.

Patch mostly by Matthias Braun
2020-09-18 14:05:18 -04:00
Matt Arsenault 870fd53e4f Reapply "RegAllocFast: Record internal state based on register units"
The regressions this caused should be fixed when
https://reviews.llvm.org/D52010 is applied.

This reverts commit a21387c654.
2020-09-18 14:05:18 -04:00
Hans Wennborg a21387c654 Revert "RegAllocFast: Record internal state based on register units"
This seems to have caused incorrect register allocation in some cases,
breaking tests in the Zig standard library (PR47278).

As discussed on the bug, revert back to green for now.

> Record internal state based on register units. This is often more
> efficient as there are typically fewer register units to update
> compared to iterating over all the aliases of a register.
>
> Original patch by Matthias Braun, but I've been rebasing and fixing it
> for almost 2 years and fixed a few bugs causing intermediate failures
> to make this patch independent of the changes in
> https://reviews.llvm.org/D52010.

This reverts commit 66251f7e1d, and
follow-ups 931a68f26b
and 0671a4c508. It also adjust some
test expectations.
2020-09-15 13:25:41 +02:00
Matt Arsenault 66251f7e1d RegAllocFast: Record internal state based on register units
Record internal state based on register units. This is often more
efficient as there are typically fewer register units to update
compared to iterating over all the aliases of a register.

Original patch by Matthias Braun, but I've been rebasing and fixing it
for almost 2 years and fixed a few bugs causing intermediate failures
to make this patch independent of the changes in
https://reviews.llvm.org/D52010.
2020-06-03 16:51:46 -04:00
Matt Arsenault 828b685ebe RegAllocFast: Improve hinting heuristic
Trace through multiple COPYs when looking for a physreg source. Add
hinting for vregs that will be copied into physregs (we only hinted
for vregs getting copied to a physreg previously).  Give hinted a
register a bonus when deciding which value to spill.  This is part of
my rewrite regallocfast series. In fact this one doesn't even have an
effect unless you also flip the allocation to happen from back to
front of a basic block. Nonetheless it helps to split this up to ease
review of D52010

Patch by Matthias Braun

llvm-svn: 360887
2019-05-16 12:50:39 +00:00
Matt Arsenault b6c599afd3 Reapply r359906, "RegAllocFast: Add heuristic to detect values not live-out of a block"
This reverts commit r359912.

This should pass now, since the clang test was made less fragile in
r359918.

llvm-svn: 359919
2019-05-03 19:06:57 +00:00
Nico Weber bb852a9672 Revert r359906, "RegAllocFast: Add heuristic to detect values not live-out of a block"
Makes clang/test/Misc/backend-stack-frame-diagnostics-fallback.cpp fail.

llvm-svn: 359912
2019-05-03 18:08:03 +00:00
Matt Arsenault daf2d653fa RegAllocFast: Add heuristic to detect values not live-out of a block
Add an improved/new heuristic to catch more cases when values are not
live out of a basic block.

Patch by Matthias Braun

llvm-svn: 359906
2019-05-03 17:03:24 +00:00
Matthias Braun 5b7c90b4e2 RegAllocFast: Leave unassigned virtreg entries in map
Set `LiveReg::PhysReg` to zero when freeing a register instead of
removing it from the entry from `LiveRegMap`. This way no iterators get
invalidated and we can avoid passing around and updating iterators all
over the place.

This does not change any allocator decisions. It is not completely NFC
because the arbitrary iteration order through `LiveRegMap` in
`spillAll()` changes so we may get a different order in those spill
sequences (the amount of spills does not change).

This is in preparation of https://reviews.llvm.org/D52010.

llvm-svn: 346298
2018-11-07 06:57:03 +00:00
Reid Kleckner 0828699488 [FastISel] Disable local value sinking by default
This is causing compilation timeouts on code with long sequences of
local values and calls (i.e. foo(1); foo(2); foo(3); ...).  It turns out
that code coverage instrumentation is a great way to create sequences
like this, which how our users ran into the issue in practice.

Intel has a tool that detects these kinds of non-linear compile time
issues, and Andy Kaylor reported it as PR37010.

The current sinking code scans the whole basic block once per local
value sink, which happens before emitting each call. In theory, local
values should only be introduced to be used by instructions between the
current flush point and the last flush point, so we should only need to
scan those instructions.

llvm-svn: 329822
2018-04-11 16:03:07 +00:00
Reid Kleckner 3a7a2e4a0a [FastISel] Sink local value materializations to first use
Summary:
Local values are constants, global addresses, and stack addresses that
can't be folded into the instruction that uses them. For example, when
storing the address of a global variable into memory, we need to
materialize that address into a register.

FastISel doesn't want to materialize any given local value more than
once, so it generates all local value materialization code at
EmitStartPt, which always dominates the current insertion point. This
allows it to maintain a map of local value registers, and it knows that
the local value area will always dominate the current insertion point.

The downside is that local value instructions are always emitted without
a source location. This is done to prevent jumpy line tables, but it
means that the local value area will be considered part of the previous
statement. Consider this C code:
  call1();      // line 1
  ++global;     // line 2
  ++global;     // line 3
  call2(&global, &local); // line 4

Today we end up with assembly and line tables like this:
  .loc 1 1
  callq call1
  leaq global(%rip), %rdi
  leaq local(%rsp), %rsi
  .loc 1 2
  addq $1, global(%rip)
  .loc 1 3
  addq $1, global(%rip)
  .loc 1 4
  callq call2

The LEA instructions in the local value area have no source location and
are treated as being on line 1. Stepping through the code in a debugger
and correlating it with the assembly won't make much sense, because
these materializations are only required for line 4.

This is actually problematic for the VS debugger "set next statement"
feature, which effectively assumes that there are no registers live
across statement boundaries. By sinking the local value code into the
statement and fixing up the source location, we can make that feature
work. This was filed as https://bugs.llvm.org/show_bug.cgi?id=35975 and
https://crbug.com/793819.

This change is obviously not enough to make this feature work reliably
in all cases, but I felt that it was worth doing anyway because it
usually generates smaller, more comprehensible -O0 code. I measured a
0.12% regression in code generation time with LLC on the sqlite3
amalgamation, so I think this is worth doing.

There are some special cases worth calling out in the commit message:
1. local values materialized for phis
2. local values used by no-op casts
3. dead local value code

Local values can be materialized for phis, and this does not show up as
a vreg use in MachineRegisterInfo. In this case, if there are no other
uses, this patch sinks the value to the first terminator, EH label, or
the end of the BB if nothing else exists.

Local values may also be used by no-op casts, which adds the register to
the RegFixups table. Without reversing the RegFixups map direction, we
don't have enough information to sink these instructions.

Lastly, if the local value register has no other uses, we can delete it.
This comes up when fastisel tries two instruction selection approaches
and the first materializes the value but fails and the second succeeds
without using the local value.

Reviewers: aprantl, dblaikie, qcolombet, MatzeB, vsk, echristo

Subscribers: dotdash, chandlerc, hans, sdardis, amccarth, javed.absar, zturner, llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D43093

llvm-svn: 327581
2018-03-14 21:54:21 +00:00
Craig Topper cc342d465e [X86] Remove llvm.x86.avx512.cvt*2mask.* intrinsics and autoupgrade to (icmp slt X, 0)
I had to drop fast-isel-abort from a test because we can't fast isel some of the mask stuff. When we used intrinsics we implicitly fell back to SelectionDAG for the intrinsic call without triggering the abort error. But with native IR that doesn't happen the same way.

llvm-svn: 322050
2018-01-09 00:50:47 +00:00
Francis Visoiu Mistrih 25528d6de7 [CodeGen] Unify MBB reference format in both MIR and debug output
As part of the unification of the debug format and the MIR format, print
MBB references as '%bb.5'.

The MIR printer prints the IR name of a MBB only for block definitions.

* find . \( -name "*.mir" -o -name "*.cpp" -o -name "*.h" -o -name "*.ll" \) -type f -print0 | xargs -0 sed -i '' -E 's/BB#" << ([a-zA-Z0-9_]+)->getNumber\(\)/" << printMBBReference(*\1)/g'
* find . \( -name "*.mir" -o -name "*.cpp" -o -name "*.h" -o -name "*.ll" \) -type f -print0 | xargs -0 sed -i '' -E 's/BB#" << ([a-zA-Z0-9_]+)\.getNumber\(\)/" << printMBBReference(\1)/g'
* find . \( -name "*.txt" -o -name "*.s" -o -name "*.mir" -o -name "*.cpp" -o -name "*.h" -o -name "*.ll" \) -type f -print0 | xargs -0 sed -i '' -E 's/BB#([0-9]+)/%bb.\1/g'
* grep -nr 'BB#' and fix

Differential Revision: https://reviews.llvm.org/D40422

llvm-svn: 319665
2017-12-04 17:18:51 +00:00
Reid Kleckner ab23dace56 [MC] Suppress .Lcfi labels when emitting textual assembly
Summary:
This suppresses the generation of .Lcfi labels in our textual assembler.
It was annoying that this generated cascading .Lcfi labels:
  llc foo.ll -o - | llvm-mc | llvm-mc

After three trips through MCAsmStreamer, we'd have three labels in the
output when none are necessary. We should only bother creating the
labels and frame data when making a real object file.

This supercedes D38605, which moved the entire .seh_ implementation into
MCObjectStreamer.

This has the advantage that we do more checking when emitting textual
assembly, as a minor efficiency cost. Outputting textual assembly is not
performance critical, so this shouldn't matter.

Reviewers: majnemer, MatzeB

Subscribers: qcolombet, nemanjai, javed.absar, eraman, hiraditya, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D38638

llvm-svn: 315259
2017-10-10 00:57:36 +00:00
Craig Topper 619b759a57 [X86] Teach fastisel to handle zext/sext i8->i16 and sext i1->i8/i16/i32/i64
Summary:
ZExt and SExt from i8 to i16 aren't implemented in the autogenerated fast isel table because normal isel does a zext/sext to 32-bits and a subreg extract to avoid a partial register write or false dependency on the upper bits of the destination. This means without handling in fast isel we end up triggering a fast isel abort.

We had no custom sign extend handling at all so while I was there I went ahead and implemented sext i1->i8/i16/i32/i64 which was also missing. This generates an i1->i8 sign extend using a mask with 1, then an 8-bit negate, then continues with a sext from i8. A better sequence would be a wider and/negate, but would require more custom code.

Fast isel tests are a mess and I couldn't find a good home for the tests so I created a new one.

The test pr34381.ll had to have fast-isel removed because it was relying on a fast isel abort to hit the bug. The test case still seems valid with fast-isel disabled though some of the instructions changed.

Reviewers: spatel, zvi, igorb, guyblank, RKSimon

Reviewed By: guyblank

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D37320

llvm-svn: 312422
2017-09-02 18:53:46 +00:00
Igor Breger a2f8ca9a34 [AVX512] Fix v8i1 /v16i1 zext + bitcast lowering pattern. Explicitly zero upper bits.
Differential Revision: http://reviews.llvm.org/D23983

llvm-svn: 280650
2016-09-05 08:26:51 +00:00