[TwoAddressInstruction] Recompute live intervals for partial defs (#74431)

Force live interval recomputation for a register if its definition is
narrowed to become partial. The live interval repair process cannot
otherwise detect these changes.

1 files changed, 11 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp b/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
index 526cb84..74d7904 100644
--- a/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
+++ b/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
@@ -1936,13 +1936,16 @@ eliminateRegSequence(MachineBasicBlock::iterator &MBBI) {
   }
 
   bool DefEmitted = false;
+  bool DefIsPartial = false;
   for (unsigned i = 1, e = MI.getNumOperands(); i < e; i += 2) {
     MachineOperand &UseMO = MI.getOperand(i);
     Register SrcReg = UseMO.getReg();
     unsigned SubIdx = MI.getOperand(i+1).getImm();
     // Nothing needs to be inserted for undef operands.
-    if (UseMO.isUndef())
+    if (UseMO.isUndef()) {
+      DefIsPartial = true;
       continue;
+    }
 
     // Defer any kill flag to the last operand using SrcReg. Otherwise, we
     // might insert a COPY that uses SrcReg after is was killed.
@@ -1987,8 +1990,14 @@ eliminateRegSequence(MachineBasicBlock::iterator &MBBI) {
     for (int j = MI.getNumOperands() - 1, ee = 0; j > ee; --j)
       MI.removeOperand(j);
   } else {
-    if (LIS)
+    if (LIS) {
+      // Force interval recomputation if we moved from full definition
+      // of register to partial.
+      if (DefIsPartial && LIS->hasInterval(DstReg) &&
+          MRI->shouldTrackSubRegLiveness(DstReg))
+        LIS->removeInterval(DstReg);
       LIS->RemoveMachineInstrFromMaps(MI);
+    }
 
     LLVM_DEBUG(dbgs() << "Eliminated: " << MI);
     MI.eraseFromParent();