1 files changed, 34 insertions, 30 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 77a8037623a..c7a199bf2e0 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -503,6 +503,40 @@ bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
     Fn.getContext().diagnose(DiagFallback);
   }
 
+  // Replace forward-declared registers with the registers containing
+  // the desired value.
+  // Note: it is important that this happens **before** the call to
+  // EmitLiveInCopies, since implementations can skip copies of unused
+  // registers. If we don't apply the reg fixups before, some registers may
+  // appear as unused and will be skipped, resulting in bad MI.
+  MachineRegisterInfo &MRI = MF->getRegInfo();
+  for (DenseMap<unsigned, unsigned>::iterator I = FuncInfo->RegFixups.begin(),
+                                              E = FuncInfo->RegFixups.end();
+       I != E; ++I) {
+    unsigned From = I->first;
+    unsigned To = I->second;
+    // If To is also scheduled to be replaced, find what its ultimate
+    // replacement is.
+    while (true) {
+      DenseMap<unsigned, unsigned>::iterator J = FuncInfo->RegFixups.find(To);
+      if (J == E)
+        break;
+      To = J->second;
+    }
+    // Make sure the new register has a sufficiently constrained register class.
+    if (TargetRegisterInfo::isVirtualRegister(From) &&
+        TargetRegisterInfo::isVirtualRegister(To))
+      MRI.constrainRegClass(To, MRI.getRegClass(From));
+    // Replace it.
+
+    // Replacing one register with another won't touch the kill flags.
+    // We need to conservatively clear the kill flags as a kill on the old
+    // register might dominate existing uses of the new register.
+    if (!MRI.use_empty(To))
+      MRI.clearKillFlags(From);
+    MRI.replaceRegWith(From, To);
+  }
+
   // If the first basic block in the function has live ins that need to be
   // copied into vregs, emit the copies into the top of the block before
   // emitting the code for the block.
@@ -622,36 +656,6 @@ bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
   // Determine if floating point is used for msvc
   computeUsesMSVCFloatingPoint(TM.getTargetTriple(), Fn, MF->getMMI());
 
-  // Replace forward-declared registers with the registers containing
-  // the desired value.
-  MachineRegisterInfo &MRI = MF->getRegInfo();
-  for (DenseMap<unsigned, unsigned>::iterator
-       I = FuncInfo->RegFixups.begin(), E = FuncInfo->RegFixups.end();
-       I != E; ++I) {
-    unsigned From = I->first;
-    unsigned To = I->second;
-    // If To is also scheduled to be replaced, find what its ultimate
-    // replacement is.
-    while (true) {
-      DenseMap<unsigned, unsigned>::iterator J = FuncInfo->RegFixups.find(To);
-      if (J == E) break;
-      To = J->second;
-    }
-    // Make sure the new register has a sufficiently constrained register class.
-    if (TargetRegisterInfo::isVirtualRegister(From) &&
-        TargetRegisterInfo::isVirtualRegister(To))
-      MRI.constrainRegClass(To, MRI.getRegClass(From));
-    // Replace it.
-
-
-    // Replacing one register with another won't touch the kill flags.
-    // We need to conservatively clear the kill flags as a kill on the old
-    // register might dominate existing uses of the new register.
-    if (!MRI.use_empty(To))
-      MRI.clearKillFlags(From);
-    MRI.replaceRegWith(From, To);
-  }
-
   TLI->finalizeLowering(*MF);
 
   // Release function-specific state. SDB and CurDAG are already cleared