[PATCH] Sink: Don't sink allocas

[Tom Stellard]

On Mon, Jan 20, 2014 at 02:58:26PM -0600, Hal Finkel wrote:
> Tom,
> 
> Do we never want to sink allocas, or just never want to sink non-dynamic ones out of the entry block? I think it is the latter, and that we still want to sink dynamic allocas. Am I missing something?

All I know for sure is that we don't want to sink non-dynamic allocas
out of the entry block.  I can modify the patch to handle only
this case, so that the we retain the old behavior in the other cases.

-Tom



> 
>  -Hal
> 
> ----- Original Message -----
> > From: "Tom Stellard" <tom at stellard.net>
> > To: "Matt Arsenault" <Matthew.Arsenault at amd.com>
> > Cc: llvm-commits at cs.uiuc.edu, "Tom Stellard" <thomas.stellard at amd.com>
> > Sent: Monday, January 20, 2014 2:53:24 PM
> > Subject: Re: [PATCH] Sink: Don't sink allocas
> > 
> > Looks like I forgot the patch...
> > 
> > On Mon, Jan 20, 2014 at 12:49:23PM -0800, Tom Stellard wrote:
> > > Hi,
> > > 
> > > Attached is an updated patch.
> > > 
> > > -Tom
> > > 
> > > On Mon, Dec 16, 2013 at 10:21:25AM -0800, Matt Arsenault wrote:
> > > > On 12/16/2013 07:17 AM, Tom Stellard wrote:
> > > > >From: Tom Stellard <thomas.stellard at amd.com>
> > > > >
> > > > >CodeGen treats allocas outside the entry block as dynamically
> > > > >sized
> > > > >stack objects.
> > > > >---
> > > > >  lib/Transforms/Scalar/Sink.cpp |  6 ++++++
> > > > >  test/Transforms/Sink/basic.ll  | 23 +++++++++++++++++++++++
> > > > >  2 files changed, 29 insertions(+)
> > > > >
> > > > >diff --git a/lib/Transforms/Scalar/Sink.cpp
> > > > >b/lib/Transforms/Scalar/Sink.cpp
> > > > >index d4595bb..c7f9e97 100644
> > > > >--- a/lib/Transforms/Scalar/Sink.cpp
> > > > >+++ b/lib/Transforms/Scalar/Sink.cpp
> > > > >@@ -218,6 +218,12 @@ bool
> > > > >Sinking::IsAcceptableTarget(Instruction *Inst,
> > > > >  /// instruction out of its current block into a successor.
> > > > >  bool Sinking::SinkInstruction(Instruction *Inst,
> > > > >                                SmallPtrSet<Instruction *, 8>
> > > > >                                &Stores) {
> > > > >+
> > > > >+  // Don't sink alloca instructions.  CodeGen assumes allocas
> > > > >outside the
> > > > >+  // entry block are dynamically sized stack objects.
> > > > >+  if (dyn_cast<AllocaInst>(Inst))
> > > > >+    return false;
> > > > >+
> > > > You don't use the value of dyn_cast, so just use isa
> > > > 
> > > > >    // Check if it's safe to move the instruction.
> > > > >    if (!isSafeToMove(Inst, AA, Stores))
> > > > >      return false;
> > > > >diff --git a/test/Transforms/Sink/basic.ll
> > > > >b/test/Transforms/Sink/basic.ll
> > > > >index 85ab376..740e5a8 100644
> > > > >--- a/test/Transforms/Sink/basic.ll
> > > > >+++ b/test/Transforms/Sink/basic.ll
> > > > >@@ -62,3 +62,26 @@ X:                                     ;
> > > > >preds = %5, %3
> > > > >    ret i32 %R
> > > > >  }
> > > > >+; We shouldn't sink allocas, since CodeGen interprets allocas
> > > > >outside the
> > > > >+; entry block as dynamically sized stack objects.
> > > > >+
> > > > >+; CHECK-LABEL: @alloca_sink
> > > > >+; CHECK: entry:
> > > > >+; CHECK-NEXT: alloca
> > > > >+define i32 @alloca_sink(i32 %a, i32 %b) {
> > > > >+entry:
> > > > >+  %0 = alloca i32
> > > > >+  %1 = icmp ne i32 %a, 0
> > > > >+  br i1 %1, label %if, label %endif
> > > > >+
> > > > >+if:
> > > > >+  %2 = getelementptr i32* %0, i32 1
> > > > >+  store i32 0, i32* %0
> > > > >+  store i32 1, i32* %2
> > > > >+  %3 = getelementptr i32* %0, i32 %b
> > > > >+  %4 = load i32* %3
> > > > >+  ret i32 %4
> > > > >+
> > > > >+endif:
> > > > >+  ret i32 0
> > > > >+}
> > > > 
> > > > 
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> > 
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> 
> -- 
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory