[llvm] r200919 - Yet another patch to reduce compile time for small programs:

[Puyan Lotfi]

Author: zer0
Date: Thu Feb  6 03:57:39 2014
New Revision: 200919

URL: http://llvm.org/viewvc/llvm-project?rev=200919&view=rev
Log:
Yet another patch to reduce compile time for small programs:

The aim in this patch is to reduce work that VirtRegRewriter needs to do when
telling MachineRegisterInfo which physregs are in use. Up until now
VirtRegRewriter::rewrite has been doing rewriting and populating def info and
then proceeding to set whether a physreg is used based this info for every
physreg that the target provides. This can be expensive when a target has an
unusually high number of supported physregs, and is a noticeable chunk of
compile time for small programs on such targets.

So to reduce compile time, this patch simply adds the use of a SparseSet to the
rewrite function that is used to flag each physreg that is encountered in a
MachineFunction. Afterward, rather than iterating over the set of all physregs
for a given target to set the physregs used in MachineRegisterInfo, the new way
is to iterate over the set of physregs that were actually encountered and set
in the SparseSet. This improves compile time because the existing rewrite
function was iterating over all MachineOperands already, and because the
iterations afterward to setPhysRegUsed is reduced by use of the SparseSet data.


Modified:
    llvm/trunk/lib/CodeGen/VirtRegMap.cpp

Modified: llvm/trunk/lib/CodeGen/VirtRegMap.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/VirtRegMap.cpp?rev=200919&r1=200918&r2=200919&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/VirtRegMap.cpp (original)
+++ llvm/trunk/lib/CodeGen/VirtRegMap.cpp Thu Feb  6 03:57:39 2014
@@ -21,6 +21,7 @@
 #include "LiveDebugVariables.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/SparseSet.h"
 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
 #include "llvm/CodeGen/LiveStackAnalysis.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
@@ -160,6 +161,7 @@ class VirtRegRewriter : public MachineFu
   SlotIndexes *Indexes;
   LiveIntervals *LIS;
   VirtRegMap *VRM;
+  SparseSet<unsigned> PhysRegs;
 
   void rewrite();
   void addMBBLiveIns();
@@ -267,6 +269,15 @@ void VirtRegRewriter::rewrite() {
   SmallVector<unsigned, 8> SuperKills;
   SmallPtrSet<const MachineInstr *, 4> NoReturnInsts;
 
+  // Here we have a SparseSet to hold which PhysRegs are actually encountered
+  // in the MF we are about to iterate over so that later when we call
+  // setPhysRegUsed, we are only doing it for physRegs that were actually found
+  // in the program and not for all of the possible physRegs for the given
+  // target architecture. If the target has a lot of physRegs, then for a small
+  // program there will be a significant compile time reduction here.
+  PhysRegs.clear();
+  PhysRegs.setUniverse(TRI->getNumRegs());
+
   for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end();
        MBBI != MBBE; ++MBBI) {
     DEBUG(MBBI->print(dbgs(), Indexes));
@@ -303,6 +314,15 @@ void VirtRegRewriter::rewrite() {
         if (MO.isRegMask())
           MRI->addPhysRegsUsedFromRegMask(MO.getRegMask());
 
+        // If we encounter a VirtReg or PhysReg then get at the PhysReg and add
+        // it to the physreg bitset.  Later we use only the PhysRegs that were
+        // actually encountered in the MF to populate the MRI's used physregs.
+        if (MO.isReg() && MO.getReg())
+          PhysRegs.insert(
+              TargetRegisterInfo::isVirtualRegister(MO.getReg()) ?
+              VRM->getPhys(MO.getReg()) :
+              MO.getReg());
+
         if (!MO.isReg() || !TargetRegisterInfo::isVirtualRegister(MO.getReg()))
           continue;
         unsigned VirtReg = MO.getReg();
@@ -376,11 +396,14 @@ void VirtRegRewriter::rewrite() {
 
   // Tell MRI about physical registers in use.
   if (NoReturnInsts.empty()) {
-    for (unsigned Reg = 1, RegE = TRI->getNumRegs(); Reg != RegE; ++Reg)
-      if (!MRI->reg_nodbg_empty(Reg))
-        MRI->setPhysRegUsed(Reg);
+    for (SparseSet<unsigned>::iterator
+        RegI = PhysRegs.begin(), E = PhysRegs.end(); RegI != E; ++RegI)
+      if (!MRI->reg_nodbg_empty(*RegI))
+        MRI->setPhysRegUsed(*RegI);
   } else {
-    for (unsigned Reg = 1, RegE = TRI->getNumRegs(); Reg != RegE; ++Reg) {
+    for (SparseSet<unsigned>::iterator
+        I = PhysRegs.begin(), E = PhysRegs.end(); I != E; ++I) {
+      unsigned Reg = *I;
       if (MRI->reg_nodbg_empty(Reg))
         continue;
       // Check if this register has a use that will impact the rest of the
@@ -397,3 +420,4 @@ void VirtRegRewriter::rewrite() {
     }
   }
 }
+