1 files changed, 19 insertions, 22 deletions

diff --git a/llvm/lib/CodeGen/PeepholeOptimizer.cpp b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
index 4507808..11acbe6 100644
--- a/llvm/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
@@ -719,15 +719,14 @@ bool PeepholeOptimizer::findNextSource(unsigned Reg, unsigned SubReg,
     CurSrcPair = Pair;
     ValueTracker ValTracker(CurSrcPair.Reg, CurSrcPair.SubReg, *MRI,
                             !DisableAdvCopyOpt, TII);
-    ValueTrackerResult Res;
-    bool ShouldRewrite = false;
 
-    do {
-      // Follow the chain of copies until we reach the top of the use-def chain
-      // or find a more suitable source.
-      Res = ValTracker.getNextSource();
+    // Follow the chain of copies until we find a more suitable source, a phi
+    // or have to abort.
+    while (true) {
+      ValueTrackerResult Res = ValTracker.getNextSource();
+      // Abort at the end of a chain (without finding a suitable source).
       if (!Res.isValid())
-        break;
+        return false;
 
       // Insert the Def -> Use entry for the recently found source.
       ValueTrackerResult CurSrcRes = RewriteMap.lookup(CurSrcPair);
@@ -763,24 +762,19 @@ bool PeepholeOptimizer::findNextSource(unsigned Reg, unsigned SubReg,
       if (TargetRegisterInfo::isPhysicalRegister(CurSrcPair.Reg))
         return false;
 
+      // Keep following the chain if the value isn't any better yet.
       const TargetRegisterClass *SrcRC = MRI->getRegClass(CurSrcPair.Reg);
-      ShouldRewrite = TRI->shouldRewriteCopySrc(DefRC, SubReg, SrcRC,
-                                                CurSrcPair.SubReg);
-    } while (!ShouldRewrite);
-
-    // Continue looking for new sources...
-    if (Res.isValid())
-      continue;
+      if (!TRI->shouldRewriteCopySrc(DefRC, SubReg, SrcRC, CurSrcPair.SubReg))
+        continue;
 
-    // Do not continue searching for a new source if the there's at least
-    // one use-def which cannot be rewritten.
-    if (!ShouldRewrite)
-      return false;
-  }
+      // We currently cannot deal with subreg operands on PHI instructions
+      // (see insertPHI()).
+      if (PHICount > 0 && CurSrcPair.SubReg != 0)
+        continue;
 
-  if (PHICount >= RewritePHILimit) {
-    DEBUG(dbgs() << "findNextSource: PHI limit reached\n");
-    return false;
+      // We found a suitable source, and are done with this chain.
+      break;
+    }
   }
 
   // If we did not find a more suitable source, there is nothing to optimize.
@@ -799,6 +793,9 @@ insertPHI(MachineRegisterInfo *MRI, const TargetInstrInfo *TII,
   assert(!SrcRegs.empty() && "No sources to create a PHI instruction?");
 
   const TargetRegisterClass *NewRC = MRI->getRegClass(SrcRegs[0].Reg);
+  // NewRC is only correct if no subregisters are involved. findNextSource()
+  // should have rejected those cases already.
+  assert(SrcRegs[0].SubReg == 0 && "should not have subreg operand");
   unsigned NewVR = MRI->createVirtualRegister(NewRC);
   MachineBasicBlock *MBB = OrigPHI->getParent();
   MachineInstrBuilder MIB = BuildMI(*MBB, OrigPHI, OrigPHI->getDebugLoc(),