RegAlloc: Use new approach to handling failed allocations (#128469)

This fixes an assert after allocation failure.

Rather than collecting failed virtual registers and hacking
on the uses after the fact, directly hack on the uses and rewrite
the registers to the dummy assignment immediately.

Previously we were bypassing LiveRegMatrix and directly assigning
in the VirtRegMap. This resulted in inconsistencies where illegal
overlapping assignments were missing. Rather than try to hack in
some system to manage these in LiveRegMatrix (i.e. hacking around
cases with invalid iterators), avoid this by directly using the
physreg. This should also allow removal of special casing in
virtregrewriter for failed allocations.

1 files changed, 3 insertions, 16 deletions

diff --git a/llvm/lib/CodeGen/VirtRegMap.cpp b/llvm/lib/CodeGen/VirtRegMap.cpp
index 4e4c89e..0fc3e5d 100644
--- a/llvm/lib/CodeGen/VirtRegMap.cpp
+++ b/llvm/lib/CodeGen/VirtRegMap.cpp
@@ -88,9 +88,7 @@ void VirtRegMap::assignVirt2Phys(Register virtReg, MCRegister physReg) {
   assert(!Virt2PhysMap[virtReg] &&
          "attempt to assign physical register to already mapped "
          "virtual register");
-  assert((!getRegInfo().isReserved(physReg) ||
-          MF->getProperties().hasProperty(
-              MachineFunctionProperties::Property::FailedRegAlloc)) &&
+  assert(!getRegInfo().isReserved(physReg) &&
          "Attempt to map virtReg to a reserved physReg");
   Virt2PhysMap[virtReg] = physReg;
 }
@@ -598,9 +596,6 @@ void VirtRegRewriter::rewrite() {
   SmallVector<Register, 8> SuperDefs;
   SmallVector<Register, 8> SuperKills;
 
-  const bool IsValidAlloc = !MF->getProperties().hasProperty(
-      MachineFunctionProperties::Property::FailedRegAlloc);
-
   for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end();
        MBBI != MBBE; ++MBBI) {
     LLVM_DEBUG(MBBI->print(dbgs(), Indexes));
@@ -620,8 +615,7 @@ void VirtRegRewriter::rewrite() {
         assert(Register(PhysReg).isPhysical());
 
         RewriteRegs.insert(PhysReg);
-        assert((!MRI->isReserved(PhysReg) || !IsValidAlloc) &&
-               "Reserved register assignment");
+        assert(!MRI->isReserved(PhysReg) && "Reserved register assignment");
 
         // Preserve semantics of sub-register operands.
         unsigned SubReg = MO.getSubReg();
@@ -696,14 +690,7 @@ void VirtRegRewriter::rewrite() {
         // Rewrite. Note we could have used MachineOperand::substPhysReg(), but
         // we need the inlining here.
         MO.setReg(PhysReg);
-
-        // Defend against generating invalid flags in allocation failure
-        // scenarios. We have have assigned a register which was undefined, or a
-        // reserved register which cannot be renamable.
-        if (LLVM_LIKELY(IsValidAlloc))
-          MO.setIsRenamable(true);
-        else if (MO.isUse())
-          MO.setIsUndef(true);
+        MO.setIsRenamable(true);
       }
 
       // Add any missing super-register kills after rewriting the whole