[llvm-commits] [llvm] r52258 - in /llvm/trunk: lib/Transforms/Scalar/LoopStrengthReduce.cpp test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness.ll
Dan Gohman
gohman at apple.com
Fri Jun 13 16:34:16 PDT 2008
On Jun 13, 2008, at 3:58 PM, Evan Cheng wrote:
>
> 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?
No; it's the condition that's important here. In the testcase,
the icmp has two users: the conditional branch at the end of the
block, and also a select instruction in the middle of the block.
The select precedes the add that LSR wants to use for the new
stride.
I'll look into the compile-time impact of traversing the block
to detect this condition.
Dan
>
>
> 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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