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0e7b9505a4
Summary: This is an extension of the fix in r271424. That fix dealt with builder insert points being moved by SCEV expansion, but only for the lifetime of the expand call. This change modifies the interface so that LSR can safely call expand multiple times at the same insert point and do the right thing if one of the expansions decides to move the original insert point. This is a fix for PR28719. Reviewers: sanjoy Subscribers: llvm-commits, mcrosier, mzolotukhin Differential Revision: https://reviews.llvm.org/D23342 llvm-svn: 278413
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))
//===---------------------------------------------------------------------===//