[PATCH] Sink: Don't sink allocas

[Tom Stellard]

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
> >+}
> 
>