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de92dc3fe2
Add an option to enable the analysis of MachineFunction register usage to extract the list of clobbered registers. When enabled, the CodeGen order is changed to be bottom up on the Call Graph. The analysis is split in two parts, RegUsageInfoCollector is the MachineFunction Pass that runs post-RA and collect the list of clobbered registers to produce a register mask. An immutable pass, RegisterUsageInfo, stores the RegMask produced by RegUsageInfoCollector, and keep them available. A future tranformation pass will use this information to update every call-sites after instruction selection. Patch by Vivek Pandya <vivekvpandya@gmail.com> Differential Revision: http://reviews.llvm.org/D20769 llvm-svn: 272403
Analysis Opportunities:
//===---------------------------------------------------------------------===//
In test/Transforms/LoopStrengthReduce/quadradic-exit-value.ll, the
ScalarEvolution expression for %r is this:
{1,+,3,+,2}<loop>
Outside the loop, this could be evaluated simply as (%n * %n), however
ScalarEvolution currently evaluates it as
(-2 + (2 * (trunc i65 (((zext i64 (-2 + %n) to i65) * (zext i64 (-1 + %n) to i65)) /u 2) to i64)) + (3 * %n))
In addition to being much more complicated, it involves i65 arithmetic,
which is very inefficient when expanded into code.
//===---------------------------------------------------------------------===//
In formatValue in test/CodeGen/X86/lsr-delayed-fold.ll,
ScalarEvolution is forming this expression:
((trunc i64 (-1 * %arg5) to i32) + (trunc i64 %arg5 to i32) + (-1 * (trunc i64 undef to i32)))
This could be folded to
(-1 * (trunc i64 undef to i32))
//===---------------------------------------------------------------------===//