From b1a005ba688397ca360e89cd6c6f51f232d6c25e Mon Sep 17 00:00:00 2001
From: Keno Fischer <keno@juliacomputing.com>
Date: Fri, 19 May 2017 18:42:20 -0400
Subject: [PATCH] [Sink] Fix predicate in legality check

Summary:
isSafeToSpeculativelyExecute is the wrong predicate to use here.
All that checks for is whether it is safe to hoist a value due to
unaligned/un-dereferencable accesses. However, not only are we doing
sinking rather than hoisting, our concern is that the location
we're loading from may have been modified. Instead forbid sinking
any load across a critical edge.

Reviewers: majnemer

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33179
---
 lib/Transforms/Scalar/Sink.cpp      |  2 +-
 test/Transforms/Sink/badloadsink.ll | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 test/Transforms/Sink/badloadsink.ll

diff --git a/lib/Transforms/Scalar/Sink.cpp b/lib/Transforms/Scalar/Sink.cpp
index 102e9ea..5210f16 100644
--- a/lib/Transforms/Scalar/Sink.cpp
+++ b/lib/Transforms/Scalar/Sink.cpp
@@ -114,7 +114,7 @@ static bool IsAcceptableTarget(Instruction *Inst, BasicBlock *SuccToSinkTo,
   if (SuccToSinkTo->getUniquePredecessor() != Inst->getParent()) {
     // We cannot sink a load across a critical edge - there may be stores in
     // other code paths.
-    if (!isSafeToSpeculativelyExecute(Inst))
+    if (isa<LoadInst>(Inst))
       return false;
 
     // We don't want to sink across a critical edge if we don't dominate the
diff --git a/test/Transforms/Sink/badloadsink.ll b/test/Transforms/Sink/badloadsink.ll
new file mode 100644
index 0000000..e3f4884
--- /dev/null
+++ b/test/Transforms/Sink/badloadsink.ll
@@ -0,0 +1,18 @@
+; RUN: opt < %s -basicaa -sink -S | FileCheck %s
+declare void @foo(i64 *)
+define i64 @sinkload(i1 %cmp) {
+; CHECK-LABEL: @sinkload
+top:
+    %a = alloca i64
+; CHECK: call void @foo(i64* %a)
+; CHECK-NEXT: %x = load i64, i64* %a
+    call void @foo(i64* %a)
+    %x = load i64, i64* %a
+    br i1 %cmp, label %A, label %B
+A:
+    store i64 0, i64 *%a
+    br label %B
+B:
+; CHECK-NOT: load i64, i64 *%a
+    ret i64 %x
+}
-- 
2.9.3