[llvm] r278584 - [IndVars] Ignore (s|z)exts that don't extend the induction variable

[Hans Wennborg via llvm-commits]

Yes! r278685.

Cheers,
Hans

On Sun, Aug 14, 2016 at 2:29 PM, David Majnemer
<david.majnemer at gmail.com> wrote:
> Hi Hans,
>
> Can we get this merged in?
>
> Thanks
>
> On Fri, Aug 12, 2016 at 5:58 PM, Sanjoy Das via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>>
>> Author: sanjoy
>> Date: Fri Aug 12 19:58:31 2016
>> New Revision: 278584
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=278584&view=rev
>> Log:
>> [IndVars] Ignore (s|z)exts that don't extend the induction variable
>>
>> `IVVisitor::visitCast` used to have the invariant that if the
>> instruction it was passed was a sext or zext instruction, the result of
>> the instruction would be wider than the induction variable.  This is no
>> longer true after rL275037, so this change teaches `IndVarSimplify` s
>> implementation of `IVVisitor::visitCast` to work with the relaxed
>> invariant.
>>
>> A corresponding change to SimplifyIndVar to preserve the said invariant
>> after rL275037 would also work, but given how `IVVisitor::visitCast` is
>> spelled (no indication of said invariant), I figured the current fix is
>> cleaner.
>>
>> Fixes PR28935.
>>
>> Added:
>>     llvm/trunk/test/Transforms/IndVarSimplify/pr28935.ll
>> Modified:
>>     llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
>>
>> Modified: llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp?rev=278584&r1=278583&r2=278584&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp (original)
>> +++ llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp Fri Aug 12
>> 19:58:31 2016
>> @@ -816,6 +816,14 @@ static void visitIVCast(CastInst *Cast,
>>    if (!Cast->getModule()->getDataLayout().isLegalInteger(Width))
>>      return;
>>
>> +  // Check that `Cast` actually extends the induction variable (we rely
>> on this
>> +  // later).  This takes care of cases where `Cast` is extending a
>> truncation of
>> +  // the narrow induction variable, and thus can end up being narrower
>> than the
>> +  // "narrow" induction variable.
>> +  uint64_t NarrowIVWidth = SE->getTypeSizeInBits(WI.NarrowIV->getType());
>> +  if (NarrowIVWidth >= Width)
>> +    return;
>> +
>>    // Cast is either an sext or zext up to this point.
>>    // We should not widen an indvar if arithmetics on the wider indvar are
>> more
>>    // expensive than those on the narrower indvar. We check only the cost
>> of ADD
>>
>> Added: llvm/trunk/test/Transforms/IndVarSimplify/pr28935.ll
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/pr28935.ll?rev=278584&view=auto
>>
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/IndVarSimplify/pr28935.ll (added)
>> +++ llvm/trunk/test/Transforms/IndVarSimplify/pr28935.ll Fri Aug 12
>> 19:58:31 2016
>> @@ -0,0 +1,20 @@
>> +; RUN: opt -S -indvars < %s | FileCheck %s
>> +
>> +target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
>> +target triple = "x86_64-unknown-linux-gnu"
>> +
>> +declare i16 @fn1(i16 returned, i64)
>> +
>> +define void @fn2() {
>> +; CHECK-LABEL: @fn2(
>> +entry:
>> +  br label %for.cond
>> +
>> +for.cond:
>> +  %f.0 = phi i64 [ undef, %entry ], [ %inc, %for.cond ]
>> +  %conv = trunc i64 %f.0 to i16
>> +  %call = tail call i16 @fn1(i16 %conv, i64 %f.0)
>> +  %conv2 = zext i16 %call to i32
>> +  %inc = add nsw i64 %f.0, 1
>> +  br label %for.cond
>> +}
>>
>>
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