[llvm-commits] [llvm] r146458 - /llvm/trunk/lib/Target/ARM/ARMConstantIslandPass.cpp

[Jakob Stoklund Olesen]

Author: stoklund
Date: Mon Dec 12 18:44:30 2011
New Revision: 146458

URL: http://llvm.org/viewvc/llvm-project?rev=146458&view=rev
Log:
Account for CPE alignment when searching for new water.

Constant pool entries with different alignment may cause more alignment
padding to be inserted. Compute the amount of padding needed, and try to
pick the location that requires the least amount of padding.

Also take the extra padding into account when the water is above the
use.

Modified:
    llvm/trunk/lib/Target/ARM/ARMConstantIslandPass.cpp

Modified: llvm/trunk/lib/Target/ARM/ARMConstantIslandPass.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMConstantIslandPass.cpp?rev=146458&r1=146457&r2=146458&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMConstantIslandPass.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMConstantIslandPass.cpp Mon Dec 12 18:44:30 2011
@@ -293,7 +293,7 @@
                       MachineInstr *CPEMI, unsigned Disp, bool NegOk,
                       bool DoDump = false);
     bool WaterIsInRange(unsigned UserOffset, MachineBasicBlock *Water,
-                        CPUser &U);
+                        CPUser &U, unsigned &Growth);
     bool BBIsInRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned Disp);
     bool FixUpImmediateBr(ImmBranch &Br);
     bool FixUpConditionalBr(ImmBranch &Br);
@@ -967,15 +967,42 @@
 
 /// WaterIsInRange - Returns true if a CPE placed after the specified
 /// Water (a basic block) will be in range for the specific MI.
-
+///
+/// Compute how much the function will grow by inserting a CPE after Water.
 bool ARMConstantIslands::WaterIsInRange(unsigned UserOffset,
-                                        MachineBasicBlock* Water, CPUser &U) {
-  unsigned CPEOffset = BBInfo[Water->getNumber()].postOffset();
+                                        MachineBasicBlock* Water, CPUser &U,
+                                        unsigned &Growth) {
+  unsigned CPELogAlign = getCPELogAlign(U.CPEMI);
+  unsigned CPEOffset = BBInfo[Water->getNumber()].postOffset(CPELogAlign);
+  unsigned NextBlockOffset, NextBlockAlignment;
+  MachineFunction::const_iterator NextBlock = Water;
+  if (++NextBlock == MF->end()) {
+    NextBlockOffset = BBInfo[Water->getNumber()].postOffset();
+    NextBlockAlignment = 0;
+  } else {
+    NextBlockOffset = BBInfo[NextBlock->getNumber()].Offset;
+    NextBlockAlignment = NextBlock->getAlignment();
+  }
+  unsigned Size = U.CPEMI->getOperand(2).getImm();
+  unsigned CPEEnd = CPEOffset + Size;
 
-  // If the CPE is to be inserted before the instruction, that will raise
-  // the offset of the instruction.
-  if (CPEOffset < UserOffset)
-    UserOffset += U.CPEMI->getOperand(2).getImm();
+  // The CPE may be able to hide in the alignment padding before the next
+  // block. It may also cause more padding to be required if it is more aligned
+  // that the next block.
+  if (CPEEnd > NextBlockOffset) {
+    Growth = CPEEnd - NextBlockOffset;
+    // Compute the padding that would go at the end of the CPE to align the next
+    // block.
+    Growth += OffsetToAlignment(CPEEnd, 1u << NextBlockAlignment);
+
+    // If the CPE is to be inserted before the instruction, that will raise
+    // the offset of the instruction.  Also account for unknown alignment padding
+    // in blocks between CPE and the user.
+    if (CPEOffset < UserOffset)
+      UserOffset += Growth + UnknownPadding(MF->getAlignment(), CPELogAlign);
+  } else
+    // CPE fits in existing padding.
+    Growth = 0;
 
   return OffsetIsInRange(UserOffset, CPEOffset, U);
 }
@@ -1130,10 +1157,9 @@
   if (WaterList.empty())
     return false;
 
-  bool FoundWaterThatWouldPad = false;
-  water_iterator IPThatWouldPad;
-  for (water_iterator IP = prior(WaterList.end()),
-         B = WaterList.begin();; --IP) {
+  unsigned BestGrowth = ~0u;
+  for (water_iterator IP = prior(WaterList.end()), B = WaterList.begin();;
+       --IP) {
     MachineBasicBlock* WaterBB = *IP;
     // Check if water is in range and is either at a lower address than the
     // current "high water mark" or a new water block that was created since
@@ -1143,30 +1169,24 @@
     // should be relatively uncommon and when it does happen, we want to be
     // sure to take advantage of it for all the CPEs near that block, so that
     // we don't insert more branches than necessary.
-    if (WaterIsInRange(UserOffset, WaterBB, U) &&
+    unsigned Growth;
+    if (WaterIsInRange(UserOffset, WaterBB, U, Growth) &&
         (WaterBB->getNumber() < U.HighWaterMark->getNumber() ||
-         NewWaterList.count(WaterBB))) {
-      unsigned WBBId = WaterBB->getNumber();
-      if (isThumb && BBInfo[WBBId].postOffset()%4 != 0) {
-        // This is valid Water, but would introduce padding.  Remember
-        // it in case we don't find any Water that doesn't do this.
-        if (!FoundWaterThatWouldPad) {
-          FoundWaterThatWouldPad = true;
-          IPThatWouldPad = IP;
-        }
-      } else {
-        WaterIter = IP;
+         NewWaterList.count(WaterBB)) && Growth < BestGrowth) {
+      // This is the least amount of required padding seen so far.
+      BestGrowth = Growth;
+      WaterIter = IP;
+      DEBUG(dbgs() << "Found water after BB#" << WaterBB->getNumber()
+                   << " Growth=" << Growth << '\n');
+
+      // Keep looking unless it is perfect.
+      if (BestGrowth == 0)
         return true;
-      }
     }
     if (IP == B)
       break;
   }
-  if (FoundWaterThatWouldPad) {
-    WaterIter = IPThatWouldPad;
-    return true;
-  }
-  return false;
+  return BestGrowth != ~0u;
 }
 
 /// CreateNewWater - No existing WaterList entry will work for