Rename ExpandISelPseudo->FinalizeISel, delay register reservation

This allows targets to make more decisions about reserved registers
after isel. For example, now it should be certain there are calls or
stack objects in the frame or not, which could have been introduced by
legalization.

Patch by Matthias Braun

llvm-svn: 363757

1 files changed, 29 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index c7a199bf2e0..5c41e6a72a5 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -656,6 +656,35 @@ 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.
+  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