Fix a bug in IfConverter with nested predicates.

Prior to this patch, IfConverter may widen the cases where a sequence of
instructions were executed because of the way it uses nested predicates. This
result in incorrect execution.

For instance, Let A be a basic block that flows conditionally into B and B be a
predicated block.
B can be predicated with A.BrToBPredicate into A iff B.Predicate is less
"permissive" than A.BrToBPredicate, i.e., iff A.BrToBPredicate subsumes
B.Predicate.

The IfConverter was checking the opposite: B.Predicate subsumes
A.BrToBPredicate.

<rdar://problem/14379453>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187071 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 3 insertions, 3 deletions

diff --git a/lib/CodeGen/IfConversion.cpp b/lib/CodeGen/IfConversion.cpp
index f4485d5d9a..1ae7e3b5ca 100644
--- a/lib/CodeGen/IfConversion.cpp
+++ b/lib/CodeGen/IfConversion.cpp
@@ -720,9 +720,9 @@ bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
   if (BBI.IsDone || BBI.IsUnpredicable)
     return false;
 
-  // If it is already predicated, check if its predicate subsumes the new
-  // predicate.
-  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
+  // If it is already predicated, check if the new predicate subsumes
+  // its predicate.
+  if (BBI.Predicate.size() && !TII->SubsumesPredicate(Pred, BBI.Predicate))
     return false;
 
   if (BBI.BrCond.size()) {