Fix PR3149. If an early clobber def is a physical register and it is tied to an input operand, it effectively extends the live range of the physical register. Currently we do not have a good way to represent this.

172     %ECX<def> = MOV32rr %reg1039<kill>
180     INLINEASM <es:subl $5,$1
        sbbl $3,$0>, 10, %EAX<def>, 14, %ECX<earlyclobber,def>, 9, %EAX<kill>,
36, <fi#0>, 1, %reg0, 0, 9, %ECX<kill>, 36, <fi#1>, 1, %reg0, 0
188     %EAX<def> = MOV32rr %EAX<kill>
196     %ECX<def> = MOV32rr %ECX<kill>
204     %ECX<def> = MOV32rr %ECX<kill>
212     %EAX<def> = MOV32rr %EAX<kill>
220     %EAX<def> = MOV32rr %EAX
228     %reg1039<def> = MOV32rr %ECX<kill>

The early clobber operand ties ECX input to the ECX def.

The live interval of ECX is represented as this:
%reg20,inf = [46,47:1)[174,230:0)  0@174-(230) 1@46-(47)

The right way to represent this is something like
%reg20,inf = [46,47:2)[174,182:1)[181:230:0)  0@174-(182) 1@181-230 @2@46-(47)

Of course that won't work since that means overlapping live ranges defined by two val#.

The workaround for now is to add a bit to val# which says the val# is redefined by a early clobber def somewhere. This prevents the move at 228 from being optimized away by SimpleRegisterCoalescing::AdjustCopiesBackFrom.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61259 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 29 insertions, 7 deletions

diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index 52b57d6d2e..1900c1a4d7 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -360,6 +360,7 @@ void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock *mbb,
         mi->getOpcode() == TargetInstrInfo::INSERT_SUBREG ||
         tii_->isMoveInstr(*mi, SrcReg, DstReg))
       CopyMI = mi;
+    // Earlyclobbers move back one.
     ValNo = interval.getNextValue(defIndex, CopyMI, VNInfoAllocator);
 
     assert(ValNo->id == 0 && "First value in interval is not 0?");
@@ -435,9 +436,8 @@ void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock *mbb,
       assert(interval.containsOneValue());
       unsigned DefIndex = getDefIndex(interval.getValNumInfo(0)->def);
       unsigned RedefIndex = getDefIndex(MIIdx);
-      // Earlyclobbers move back one.
-      if (MO.isEarlyClobber())
-        RedefIndex = getUseIndex(MIIdx);
+      // It cannot be an early clobber MO.
+      assert(!MO.isEarlyClobber() && "Unexpected early clobber!");
 
       const LiveRange *OldLR = interval.getLiveRangeContaining(RedefIndex-1);
       VNInfo *OldValNo = OldLR->valno;
@@ -505,9 +505,8 @@ void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock *mbb,
       // live until the end of the block.  We've already taken care of the
       // rest of the live range.
       unsigned defIndex = getDefIndex(MIIdx);
-      // Earlyclobbers move back one.
-      if (MO.isEarlyClobber())
-        defIndex = getUseIndex(MIIdx);
+      // It cannot be an early clobber MO.
+      assert(!MO.isEarlyClobber() && "Unexpected early clobber!");
       
       VNInfo *ValNo;
       MachineInstr *CopyMI = NULL;
@@ -592,8 +591,11 @@ exit:
 
   // Already exists? Extend old live interval.
   LiveInterval::iterator OldLR = interval.FindLiveRangeContaining(start);
-  VNInfo *ValNo = (OldLR != interval.end())
+  bool Extend = OldLR != interval.end();
+  VNInfo *ValNo = Extend
     ? OldLR->valno : interval.getNextValue(start, CopyMI, VNInfoAllocator);
+  if (MO.isEarlyClobber() && Extend)
+    ValNo->redefByEC = true;
   LiveRange LR(start, end, ValNo);
   interval.addRange(LR);
   interval.addKill(LR.valno, end);
diff --git a/lib/CodeGen/SimpleRegisterCoalescing.cpp b/lib/CodeGen/SimpleRegisterCoalescing.cpp
index 41022a6e26..cfac82613f 100644
--- a/lib/CodeGen/SimpleRegisterCoalescing.cpp
+++ b/lib/CodeGen/SimpleRegisterCoalescing.cpp
@@ -119,6 +119,26 @@ bool SimpleRegisterCoalescing::AdjustCopiesBackFrom(LiveInterval &IntA,
   if (ALR == IntA.end()) // Should never happen!
     return false;
   VNInfo *AValNo = ALR->valno;
+  // If it's re-defined by an early clobber somewhere in the live range, then
+  // it's not safe to eliminate the copy. FIXME: This is a temporary workaround.
+  // See PR3149:
+  // 172     %ECX<def> = MOV32rr %reg1039<kill>
+  // 180     INLINEASM <es:subl $5,$1
+  //         sbbl $3,$0>, 10, %EAX<def>, 14, %ECX<earlyclobber,def>, 9, %EAX<kill>,
+  // 36, <fi#0>, 1, %reg0, 0, 9, %ECX<kill>, 36, <fi#1>, 1, %reg0, 0
+  // 188     %EAX<def> = MOV32rr %EAX<kill>
+  // 196     %ECX<def> = MOV32rr %ECX<kill>
+  // 204     %ECX<def> = MOV32rr %ECX<kill>
+  // 212     %EAX<def> = MOV32rr %EAX<kill>
+  // 220     %EAX<def> = MOV32rr %EAX
+  // 228     %reg1039<def> = MOV32rr %ECX<kill>
+  // The early clobber operand ties ECX input to the ECX def.
+  //
+  // The live interval of ECX is represented as this:
+  // %reg20,inf = [46,47:1)[174,230:0)  0@174-(230) 1@46-(47)
+  // The coalescer has no idea there was a def in the middle of [174,230].
+  if (AValNo->redefByEC)
+    return false;
   
   // If AValNo is defined as a copy from IntB, we can potentially process this.  
   // Get the instruction that defines this value number.