[llvm] r256338 - [SCEV] Fix getLoopBackedgeTakenCounts

[Bill Seurer via llvm-commits]

I agree it looks broken.  Several of the buildbots are failing here:

/home/buildbots/ppc64be-llvm-quick/llvm-ppc64-2/llvm.src/lib/Analysis/ScalarEvolution.cpp: 
In function ‘void getLoopBackedgeTakenCounts(llvm::Loop*, VerifyMap&, 
llvm::ScalarEvolution&)’:
/home/buildbots/ppc64be-llvm-quick/llvm-ppc64-2/llvm.src/lib/Analysis/ScalarEvolution.cpp:9456:27: 
error: use of ‘L’ before deduction of ‘auto’
    for (auto *L : reverse(*L))
                            ^


On 12/23/15 12:22, JF Bastien via llvm-commits wrote:
> Seems broken, I think r256338 fixes it.
>
> On Wed, Dec 23, 2015 at 9:48 AM, Sanjoy Das via llvm-commits
> <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
>
>     Author: sanjoy
>     Date: Wed Dec 23 11:48:14 2015
>     New Revision: 256338
>
>     URL: http://llvm.org/viewvc/llvm-project?rev=256338&view=rev
>     Log:
>     [SCEV] Fix getLoopBackedgeTakenCounts
>
>     The way `getLoopBackedgeTakenCounts` is written right now isn't
>     correct. It will try to compute and store the BE counts of a Loop
>       #{child loop} number of times (which may be zero).
>
>     Modified:
>          llvm/trunk/lib/Analysis/ScalarEvolution.cpp
>
>     Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
>     URL:
>     http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=256338&r1=256337&r2=256338&view=diff
>     ==============================================================================
>     --- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
>     +++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Wed Dec 23 11:48:14 2015
>     @@ -9439,23 +9439,22 @@ static void replaceSubString(std::string
>       /// getLoopBackedgeTakenCounts - Helper method for verifyAnalysis.
>       static void
>       getLoopBackedgeTakenCounts(Loop *L, VerifyMap &Map,
>     ScalarEvolution &SE) {
>     -  for (Loop::reverse_iterator I = L->rbegin(), E = L->rend(); I !=
>     E; ++I) {
>     -    getLoopBackedgeTakenCounts(*I, Map, SE); // recurse.
>     +  std::string &S = Map[L];
>     +  if (S.empty()) {
>     +    raw_string_ostream OS(S);
>     +    SE.getBackedgeTakenCount(L)->print(OS);
>
>     -    std::string &S = Map[L];
>     -    if (S.empty()) {
>     -      raw_string_ostream OS(S);
>     -      SE.getBackedgeTakenCount(L)->print(OS);
>     -
>     -      // false and 0 are semantically equivalent. This can happen
>     in dead loops.
>     -      replaceSubString(OS.str(), "false", "0");
>     -      // Remove wrap flags, their use in SCEV is highly fragile.
>     -      // FIXME: Remove this when SCEV gets smarter about them.
>     -      replaceSubString(OS.str(), "<nw>", "");
>     -      replaceSubString(OS.str(), "<nsw>", "");
>     -      replaceSubString(OS.str(), "<nuw>", "");
>     -    }
>     +    // false and 0 are semantically equivalent. This can happen in
>     dead loops.
>     +    replaceSubString(OS.str(), "false", "0");
>     +    // Remove wrap flags, their use in SCEV is highly fragile.
>     +    // FIXME: Remove this when SCEV gets smarter about them.
>     +    replaceSubString(OS.str(), "<nw>", "");
>     +    replaceSubString(OS.str(), "<nsw>", "");
>     +    replaceSubString(OS.str(), "<nuw>", "");
>         }
>     +
>     +  for (auto *L : reverse(*L))
>     +    getLoopBackedgeTakenCounts(L, Map, SE); // recurse.
>       }
>
>       void ScalarEvolution::verify() const {
>
>
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-- 

-Bill Seurer