[llvm-commits] [llvm] r157701 - in /llvm/trunk: include/llvm/Analysis/ScalarEvolution.h lib/Analysis/ScalarEvolution.cpp test/Transforms/IndVarSimplify/ult-sub-to-eq.ll

[Benjamin Kramer]

On 30.05.2012, at 20:39, Eli Friedman wrote:

> On Wed, May 30, 2012 at 11:32 AM, Benjamin Kramer
> <benny.kra at googlemail.com> wrote:
>> Author: d0k
>> Date: Wed May 30 13:32:23 2012
>> New Revision: 157701
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=157701&view=rev
>> Log:
>> Teach SCEV's icmp simplification logic that a-b == 0 is equivalent to a == b.
>> 
>> This also required making recursive simplifications until
>> nothing changes or a hard limit (currently 3) is hit.
>> 
>> With the simplification in place indvars can canonicalize
>> loops of the form
>> for (unsigned i = 0; i < a-b; ++i)
>> into
>> for (unsigned i = 0; i != a-b; ++i)
>> which used to fail because SCEV created a weird umax expr
>> for the backedge taken count.
>> 
>> Added:
>>    llvm/trunk/test/Transforms/IndVarSimplify/ult-sub-to-eq.ll
>> Modified:
>>    llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
>>    llvm/trunk/lib/Analysis/ScalarEvolution.cpp
>> 
>> Modified: llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/ScalarEvolution.h?rev=157701&r1=157700&r2=157701&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm/Analysis/ScalarEvolution.h (original)
>> +++ llvm/trunk/include/llvm/Analysis/ScalarEvolution.h Wed May 30 13:32:23 2012
>> @@ -837,7 +837,8 @@
>>     ///
>>     bool SimplifyICmpOperands(ICmpInst::Predicate &Pred,
>>                               const SCEV *&LHS,
>> -                              const SCEV *&RHS);
>> +                              const SCEV *&RHS,
>> +                              unsigned Depth = 0);
>> 
>>     /// getLoopDisposition - Return the "disposition" of the given SCEV with
>>     /// respect to the given loop.
>> 
>> Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=157701&r1=157700&r2=157701&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
>> +++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Wed May 30 13:32:23 2012
>> @@ -5605,9 +5605,14 @@
>>  /// predicate Pred. Return true iff any changes were made.
>>  ///
>>  bool ScalarEvolution::SimplifyICmpOperands(ICmpInst::Predicate &Pred,
>> -                                           const SCEV *&LHS, const SCEV *&RHS) {
>> +                                           const SCEV *&LHS, const SCEV *&RHS,
>> +                                           unsigned Depth) {
>>   bool Changed = false;
>> 
>> +  // If we hit the max recursion limit bail out.
>> +  if (Depth >= 3)
>> +    return false;
>> +
>>   // Canonicalize a constant to the right side.
>>   if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS)) {
>>     // Check for both operands constant.
>> @@ -5645,6 +5650,15 @@
>>     default: llvm_unreachable("Unexpected ICmpInst::Predicate value!");
>>     case ICmpInst::ICMP_EQ:
>>     case ICmpInst::ICMP_NE:
>> +      // Fold ((-1) * %a) + %b == 0 (equivalent to %b-%a == 0) into %a == %b.
>> +      if (!RA)
>> +        if (const SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(LHS))
>> +          if (const SCEVMulExpr *ME = dyn_cast<SCEVMulExpr>(AE->getOperand(0)))
>> +            if (ME->getOperand(0)->isAllOnesValue()) {
>> +              RHS = AE->getOperand(1);
>> +              LHS = ME->getOperand(1);
>> +              Changed = true;
> 
> Err, SCEVAddExpr can have more than 2 operands...

Sigh, I wish SCEV would match IR more closely. Limited it to 2 operands in r157704.

- Ben