Fix live variables issues:

1. If part of a register is re-defined, an implicit kill and an implicit def are added to denote read / mod / write. However, this should only be necessary if the register is actually read later. This is a performance issue.
2. If a sub-register is being defined, and it doesn't have a previous use, do not add a implicit kill to the last use of a super-register:
   = EAX, AX<imp-use,kill>
...
AX =
In this case, EAX is live but AX is killed, this is wrong and will cause the coalescer to do bad things.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48521 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 0 deletions

diff --git a/include/llvm/CodeGen/LiveVariables.h b/include/llvm/CodeGen/LiveVariables.h
index aa3b765..977b87a 100644
--- a/include/llvm/CodeGen/LiveVariables.h
+++ b/include/llvm/CodeGen/LiveVariables.h
@@ -165,6 +165,12 @@ private:   // Intermediate data structures
   void HandlePhysRegUse(unsigned Reg, MachineInstr *MI);
   void HandlePhysRegDef(unsigned Reg, MachineInstr *MI);
 
+  /// hasRegisterUseBelow - Return true if the specified register is used after
+  /// the current instruction and before it's next definition.
+  bool hasRegisterUseBelow(unsigned Reg,
+                           MachineBasicBlock::iterator I,
+                           MachineBasicBlock *MBB);
+
   /// analyzePHINodes - Gather information about the PHI nodes in here. In
   /// particular, we want to map the variable information of a virtual
   /// register which is used in a PHI node. We map that to the BB the vreg