[AggressiveAntiDepBreaker] Check for EarlyClobber on defining instruction

AggressiveAntiDepBreaker was doing some EarlyClobber checking, but was not
checking that the register being potentially renamed was defined by an
early-clobber def where there was also a use, in that instruction, of the
register being considered as the target of the rename. Fixes PR24014.

llvm-svn: 246423

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/AggressiveAntiDepBreaker.cpp b/llvm/lib/CodeGen/AggressiveAntiDepBreaker.cpp
index 3ac5a440094..7ba67687922 100644
--- a/llvm/lib/CodeGen/AggressiveAntiDepBreaker.cpp
+++ b/llvm/lib/CodeGen/AggressiveAntiDepBreaker.cpp
@@ -689,6 +689,20 @@ bool AggressiveAntiDepBreaker::FindSuitableFreeRegisters(
         }
       }
 
+      // Also, we cannot rename 'Reg' to 'NewReg' if the instruction defining
+      // 'Reg' is an early-clobber define and that instruction also uses
+      // 'NewReg'.
+      for (const auto &Q : make_range(RegRefs.equal_range(Reg))) {
+        if (!Q.second.Operand->isDef() || !Q.second.Operand->isEarlyClobber())
+          continue;
+
+        MachineInstr *DefMI = Q.second.Operand->getParent();
+        if (DefMI->readsRegister(NewReg, TRI)) {
+          DEBUG(dbgs() << "(ec)");
+          goto next_super_reg;
+        }
+      }
+
       // Record that 'Reg' can be renamed to 'NewReg'.
       RenameMap.insert(std::pair<unsigned, unsigned>(Reg, NewReg));
     }