[PATCH] D33179: [Sink] Fix predicate in legality check

[Keno Fischer via Phabricator via llvm-commits]

loladiro created this revision.

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.


https://reviews.llvm.org/D33179

Files:
  lib/Transforms/Scalar/Sink.cpp
  test/Transforms/Sink/badloadsink.ll


Index: test/Transforms/Sink/badloadsink.ll
===================================================================
--- /dev/null
+++ 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
+}
Index: lib/Transforms/Scalar/Sink.cpp
===================================================================
--- lib/Transforms/Scalar/Sink.cpp
+++ lib/Transforms/Scalar/Sink.cpp
@@ -114,7 +114,7 @@
   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


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