Commit Graph

5 Commits

Author SHA1 Message Date
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