Reuse lowered phi nodes.
Tail duplication produces lots of identical phi nodes in different basic
blocks. Teach PHIElimination to reuse the join registers when lowering a phi
node that is identical to an already lowered node. This saves virtual
registers, and more importantly it avoids creating copies the the coalescer
doesn't know how to eliminate.
Teach LiveIntervalAnalysis about the phi joins with multiple uses.
This patch significantly reduces code size produced by -pre-regalloc-taildup.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91549 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/PHIElimination.h b/lib/CodeGen/PHIElimination.h
index b0b71ce..1bcc9dc 100644
--- a/lib/CodeGen/PHIElimination.h
+++ b/lib/CodeGen/PHIElimination.h
@@ -16,8 +16,6 @@
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/Target/TargetInstrInfo.h"
-#include <map>
-
namespace llvm {
/// Lower PHI instructions to copies.
@@ -120,8 +118,8 @@
return I;
}
- typedef std::pair<const MachineBasicBlock*, unsigned> BBVRegPair;
- typedef std::map<BBVRegPair, unsigned> VRegPHIUse;
+ typedef std::pair<unsigned, unsigned> BBVRegPair;
+ typedef DenseMap<BBVRegPair, unsigned> VRegPHIUse;
VRegPHIUse VRegPHIUseCount;
PHIDefMap PHIDefs;
@@ -129,6 +127,17 @@
// Defs of PHI sources which are implicit_def.
SmallPtrSet<MachineInstr*, 4> ImpDefs;
+
+ // Lowered PHI nodes may be reused. We provide special DenseMap traits to
+ // match PHI nodes with identical arguments.
+ struct PHINodeTraits : public DenseMapInfo<MachineInstr*> {
+ static unsigned getHashValue(const MachineInstr *PtrVal);
+ static bool isEqual(const MachineInstr *LHS, const MachineInstr *RHS);
+ };
+
+ // Map reusable lowered PHI node -> incoming join register.
+ typedef DenseMap<MachineInstr*, unsigned, PHINodeTraits> LoweredPHIMap;
+ LoweredPHIMap LoweredPHIs;
};
}