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[oota-llvm.git] / lib / CodeGen / RegisterCoalescer.cpp

diff --git a/lib/CodeGen/RegisterCoalescer.cpp b/lib/CodeGen/RegisterCoalescer.cpp
index 9b52d9b126b4f29a2f36323351df37157d73a021..1e1a42451485223c9ef68087ca05d31eab73d2f4 100644 (file)
--- a/lib/CodeGen/RegisterCoalescer.cpp
+++ b/lib/CodeGen/RegisterCoalescer.cpp
@@ -16,9 +16,6 @@
 #define DEBUG_TYPE "regalloc"
 #include "RegisterCoalescer.h"
 #include "LiveDebugVariables.h"
-
-#include "llvm/Pass.h"
-#include "llvm/Value.h"
 #include "llvm/ADT/OwningPtr.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallSet.h"
@@ -33,6 +30,7 @@
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/CodeGen/RegisterClassInfo.h"
 #include "llvm/CodeGen/VirtRegMap.h"
+#include "llvm/Pass.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -42,6 +40,7 @@
 #include "llvm/Target/TargetOptions.h"
 #include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
+#include "llvm/Value.h"
 #include <algorithm>
 #include <cmath>
 using namespace llvm;
@@ -887,8 +886,17 @@ void RegisterCoalescer::updateRegDefsUses(unsigned SrcReg,
   // Update LiveDebugVariables.
   LDV->renameRegister(SrcReg, DstReg, SubIdx);
 
+  SmallPtrSet<MachineInstr*, 8> Visited;
   for (MachineRegisterInfo::reg_iterator I = MRI->reg_begin(SrcReg);
        MachineInstr *UseMI = I.skipInstruction();) {
+    // Each instruction can only be rewritten once because sub-register
+    // composition is not always idempotent. When SrcReg != DstReg, rewriting
+    // the UseMI operands removes them from the SrcReg use-def chain, but when
+    // SrcReg is DstReg we could encounter UseMI twice if it has multiple
+    // operands mentioning the virtual register.
+    if (SrcReg == DstReg && !Visited.insert(UseMI))
+      continue;
+
     SmallVector<unsigned,8> Ops;
     bool Reads, Writes;
     tie(Reads, Writes) = UseMI->readsWritesVirtualRegister(SrcReg, &Ops);