llvm-6502/test/Analysis/ScalarEvolution/2008-08-04-IVOverflow.ll
Eli Friedman b42a626122 PR2621: Improvements to the SCEV AddRec binomial expansion. This
version uses a new algorithm for evaluating the binomial coefficients 
which is significantly more efficient for AddRecs of more than 2 terms 
(see the comments in the code for details on how the algorithm works).  
It also fixes some bugs: it removes the arbitrary length restriction for 
AddRecs, it fixes the silent generation of incorrect code for AddRecs 
which require a wide calculation width, and it fixes an issue where we 
were incorrectly truncating the iteration count too far when evaluating 
an AddRec expression narrower than the induction variable.

There are still a few related issues I know of: I think there's 
still an issue with the SCEVExpander expansion of AddRec in terms of
the width of the induction variable used.  The hack to avoid generating 
too-wide integers shouldn't be necessary; instead, the callers should be 
considering the cost of the expansion before expanding it (in addition 
to not expanding too-wide integers, we might not want to expand 
expressions that are really expensive, especially when optimizing for 
size; calculating an length-17 32-bit AddRec currently generates about 250 
instructions of straight-line code on X86).  Also, for long 32-bit 
AddRecs on X86, CodeGen really sucks at scheduling the code.  I'm planning on 
filing follow-up PRs for these issues.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@54332 91177308-0d34-0410-b5e6-96231b3b80d8
2008-08-04 23:49:06 +00:00

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LLVM

; RUN: llvm-as < %s | opt -analyze -scalar-evolution -disable-output \
; RUN: -scalar-evolution-max-iterations=0 | grep -F "Exits: 20028"
; PR2621
define i32 @a() nounwind {
entry:
br label %bb1
bb:
trunc i32 %i.0 to i16
add i16 %0, %x16.0
add i32 %i.0, 1
br label %bb1
bb1:
%i.0 = phi i32 [ 0, %entry ], [ %2, %bb ]
%x16.0 = phi i16 [ 0, %entry ], [ %1, %bb ]
icmp ult i32 %i.0, 888888
br i1 %3, label %bb, label %bb2
bb2:
zext i16 %x16.0 to i32
ret i32 %4
}