mirror of
https://github.com/RPCS3/llvm.git
synced 2025-01-13 07:50:50 +00:00
cc99164448
Summary: MemoryDependenceAnalysis is currently cautious when the QueryInstr is an atomic load or store, but I forgot to check for atomic cmpxchg/atomicrmw. This patch is a way of fixing that, and making it less brittle (i.e. no risk that I forget another possible kind of atomic, even if the IR ends up changing in the future), by adding a fallback checking mayReadOrWriteFromMemory. Thanks to Philip Reames for finding this bug and suggesting this solution in http://reviews.llvm.org/D4845 Sadly, I don't see how to add a test for this, since the passes depending on MemoryDependenceAnalysis won't trigger for an atomic rmw anyway. Does anyone see a way for testing it? Test Plan: none possible at first sight Reviewers: jfb, reames Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D5019 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216940 91177308-0d34-0410-b5e6-96231b3b80d8
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))
//===---------------------------------------------------------------------===//