[llvm-commits] [llvm] r52258 - in /llvm/trunk: lib/Transforms/Scalar/LoopStrengthReduce.cpp test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness.ll

[Evan Cheng]

On Jun 13, 2008, at 3:48 PM, Dan Gohman wrote:

> No, it's still possible to eliminate an iv when the condition has
> multiple users. But it's complicated when the iv to be used in the

The only time that's possible is if all the other uses are memory  
operations, right?

Evan

>
> new condition is defined later in the block than one of the
> condition's users.
>
> Dan
>
> On Jun 13, 2008, at 3:28 PM, Evan Cheng wrote:
>
>> Ah ok. I think this is not overly conservative. If there are multiple
>> uses, it's probably not profitable to make the transformation anyway
>> since it will not be able to eliminate an iv, right?
>>
>> Evan
>>
>> On Jun 13, 2008, at 2:43 PM, Dan Gohman wrote:
>>
>>> Author: djg
>>> Date: Fri Jun 13 16:43:41 2008
>>> New Revision: 52258
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=52258&view=rev
>>> Log:
>>> Protect ChangeCompareStride from situations in which it is possible
>>> for it to generate use-before-def IR, such as in this testcase.
>>>
>>> Added:
>>>  llvm/trunk/test/Transforms/LoopStrengthReduce/change-compare-
>>> stride-trickiness.ll
>>> Modified:
>>>  llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp
>>>
>>> Modified: llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp?rev=52258&r1=52257&r2=52258&view=diff
>>>
>>> =
>>> =
>>> =
>>> =
>>> =
>>> =
>>> =
>>> =
>>> =
>>> = 
>>> ====================================================================
>>> --- llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp
>>> (original)
>>> +++ llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp Fri Jun
>>> 13 16:43:41 2008
>>> @@ -1529,6 +1529,15 @@
>>> ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst
>>> *Cond,
>>>                                               IVStrideUse* &CondUse,
>>>                                               const SCEVHandle*
>>> &CondStride) {
>>> +  // Forgo this transformation if the condition has multiple uses.
>>> This is
>>> +  // over-conservative, but simpler than alternatives. It guards
>>> against
>>> +  // comparisons with a use that occurs earlier than the add
>>> instruction for the
>>> +  // new stride index.  See
>>> +  // test/Transforms/LoopStrengthReduce/change-compare-stride-
>>> trickiness.ll
>>> +  // for an example of this situation.
>>> +  if (!Cond->hasOneUse())
>>> +    return Cond;
>>> +
>>> if (StrideOrder.size() < 2 ||
>>>     IVUsesByStride[*CondStride].Users.size() != 1)
>>>   return Cond;
>>> @@ -1654,9 +1663,9 @@
>>>     RHS = SCEVExpander::InsertCastOfTo(Instruction::IntToPtr, RHS,
>>> NewCmpTy);
>>>   }
>>>   // Insert new compare instruction.
>>> -    Cond = new ICmpInst(Predicate, NewIncV, RHS);
>>> -    Cond->setName(L->getHeader()->getName() + ".termcond");
>>> -    OldCond->getParent()->getInstList().insert(OldCond, Cond);
>>> +    Cond = new ICmpInst(Predicate, NewIncV, RHS,
>>> +                        L->getHeader()->getName() + ".termcond",
>>> +                        OldCond);
>>>
>>>   // Remove the old compare instruction. The old indvar is
>>> probably dead too.
>>>   DeadInsts.insert(cast<Instruction>(CondUse->OperandValToReplace));
>>>
>>> Added: llvm/trunk/test/Transforms/LoopStrengthReduce/change-compare-
>>> stride-trickiness.ll
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness.ll?rev=52258&view=auto
>>>
>>> =
>>> =
>>> =
>>> =
>>> =
>>> =
>>> =
>>> =
>>> =
>>> = 
>>> ====================================================================
>>> --- llvm/trunk/test/Transforms/LoopStrengthReduce/change-compare-
>>> stride-trickiness.ll (added)
>>> +++ llvm/trunk/test/Transforms/LoopStrengthReduce/change-compare-
>>> stride-trickiness.ll Fri Jun 13 16:43:41 2008
>>> @@ -0,0 +1,20 @@
>>> +; RUN: llvm-as < %s | llc
>>> +target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16- 
>>> i32:32:32-
>>> i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-
>>> s0:64:64-f80:128:128"
>>> +target triple = "x86_64-apple-darwin9"
>>> +
>>> +define void @foo() {
>>> +entry:
>>> +	br label %loop
>>> +
>>> +loop:
>>> +	%indvar = phi i32 [ 0, %entry ], [ %i.2.0.us1534, %loop ]		; <i32>
>>> [#uses=1]
>>> +	%i.2.0.us1534 = add i32 %indvar, 1		; <i32> [#uses=3]
>>> +	%tmp611.us1535 = icmp eq i32 %i.2.0.us1534, 4		; <i1> [#uses=2]
>>> +	%tmp623.us1538 = select i1 %tmp611.us1535, i32 6, i32 0		; <i32>
>>> [#uses=0]
>>> +	%tmp628.us1540 = shl i32 %i.2.0.us1534, 1		; <i32> [#uses=1]
>>> +	%tmp645646647.us1547 = sext i32 %tmp628.us1540 to i64		; <i64>
>>> [#uses=0]
>>> +	br i1 %tmp611.us1535, label %exit, label %loop
>>> +
>>> +exit:
>>> +	ret void
>>> +}
>>>
>>>
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