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cc3d0eb483
the example in GCC PR16799 to: LBB1_2: ## %bb1 movl %eax, %eax subq %rax, %rdi movq %rdi, (%rcx) movl (%rdi), %eax testl %eax, %eax je LBB1_2 instead of: LBB1_2: ## %bb1 movl (%rdi), %ecx subq %rcx, %rdi movq %rdi, (%rax) cmpl $0, (%rdi) je LBB1_2 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89978 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.
//===---------------------------------------------------------------------===//