[BranchRelaxation] Correct JumpToFT value

Toggle true/false values of the JumpToFallThrough
parameter to simplify code and make it consistent
with the documentation for the `getFallThrough(..)`
method.

Reviewed By: bcahoon

Differential Revision: https://reviews.llvm.org/D148139

Author: gandhi56

llvm/include/llvm/CodeGen/MachineBasicBlock.h

@@ -796,12 +796,12 @@ class MachineBasicBlock
   /// it. If an explicit branch to the fallthrough block is not allowed,
   /// set JumpToFallThrough to be false. Non-null return is a conservative
   /// answer.
-  MachineBasicBlock *getFallThrough(bool JumpToFallThrough = false);
+  MachineBasicBlock *getFallThrough(bool JumpToFallThrough = true);
 
   /// Return the fallthrough block if the block can implicitly
   /// transfer control to it's successor, whether by a branch or
   /// a fallthrough. Non-null return is a conservative answer.
-  MachineBasicBlock *getLogicalFallThrough() { return getFallThrough(true); }
+  MachineBasicBlock *getLogicalFallThrough() { return getFallThrough(false); }
 
   /// Return true if the block can implicitly transfer control to the
   /// block after it by falling off the end of it.  This should return

llvm/lib/CodeGen/MachineBasicBlock.cpp

@@ -975,8 +975,8 @@ MachineBasicBlock *MachineBasicBlock::getFallThrough(bool JumpToFallThrough) {
 
   // If there is some explicit branch to the fallthrough block, it can obviously
   // reach, even though the branch should get folded to fall through implicitly.
-  if (!JumpToFallThrough && (MachineFunction::iterator(TBB) == Fallthrough ||
-                           MachineFunction::iterator(FBB) == Fallthrough))
+  if (JumpToFallThrough && (MachineFunction::iterator(TBB) == Fallthrough ||
+                            MachineFunction::iterator(FBB) == Fallthrough))
     return &*Fallthrough;
 
   // If it's an unconditional branch to some block not the fall through, it