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ed504111e8
function to every defined function known to LLVM as a library function. LLVM can introduce calls to these functions either by replacing other library calls or by recognizing patterns (such as memset_pattern or vector math patterns) and replacing those with calls. When these library functions are actually defined in the module, we need to have reference edges to them initially so that we visit them during the CGSCC walk in the right order and can effectively rebuild the call graph afterward. This was discovered when building code with Fortify enabled as that is a common case of both inline definitions of library calls and simplifications of code into calling them. This can in extreme cases of LTO-ing with libc introduce *many* more reference edges. I discussed a bunch of different options with folks but all of them are unsatisfying. They either make the graph operations substantially more complex even when there are *no* defined libfuncs, or they introduce some other complexity into the callgraph. So this patch goes with the simplest possible solution of actual synthetic reference edges. If this proves to be a memory problem, I'm happy to implement one of the clever techniques to save memory here. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@308088 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))
//===---------------------------------------------------------------------===//