[MachineCSE] Add new callback for is caller preserved or constant physregs

The instructions addis,addi, bl are used to calculate the address of TLS thread
local variables. These TLS access code sequences are generated repeatedly every
time the thread local variable is accessed. By communicating to Machine CSE that
X2 is guaranteed to have the same value within the same function call (so called
Caller Preserved Physical Register), the redundant TLS access code sequences are
cleaned up.

Differential Revision: https://reviews.llvm.org/D39173

llvm-svn: 318661

2 files changed, 9 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/MachineCSE.cpp b/llvm/lib/CodeGen/MachineCSE.cpp
index 32e57a9f938..aaac6ad9336 100644
--- a/llvm/lib/CodeGen/MachineCSE.cpp
+++ b/llvm/lib/CodeGen/MachineCSE.cpp
@@ -250,8 +250,8 @@ bool MachineCSE::hasLivePhysRegDefUses(const MachineInstr *MI,
       continue;
     if (TargetRegisterInfo::isVirtualRegister(Reg))
       continue;
-    // Reading constant physregs is ok.
-    if (!MRI->isConstantPhysReg(Reg))
+    // Reading either caller preserved or constant physregs is ok.
+    if (!MRI->isCallerPreservedOrConstPhysReg(Reg))
       for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
         PhysRefs.insert(*AI);
   }
diff --git a/llvm/lib/CodeGen/MachineRegisterInfo.cpp b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
index 84d130fae3c..dfa0a4af334 100644
--- a/llvm/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
@@ -487,6 +487,13 @@ bool MachineRegisterInfo::isConstantPhysReg(unsigned PhysReg) const {
   return true;
 }
 
+bool
+MachineRegisterInfo::isCallerPreservedOrConstPhysReg(unsigned PhysReg) const {
+  const TargetRegisterInfo *TRI = getTargetRegisterInfo();
+  return isConstantPhysReg(PhysReg) ||
+      TRI->isCallerPreservedPhysReg(PhysReg, *MF);
+}
+
 /// markUsesInDebugValueAsUndef - Mark every DBG_VALUE referencing the
 /// specified register as undefined which causes the DBG_VALUE to be
 /// deleted during LiveDebugVariables analysis.