When SimpleRegisterCoalescing is trimming kill flags on a physical register

operand, also check if subregisters are killed.

Add <imp-def> operands for subregisters that remain alive after a super register
is killed.

I don't have a testcase for this that reproduces on trunk. <rdar://problem/8441758>

llvm-svn: 116940

1 files changed, 11 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SimpleRegisterCoalescing.cpp b/llvm/lib/CodeGen/SimpleRegisterCoalescing.cpp
index 41be8d551f5..2f73551aa6d 100644
--- a/llvm/lib/CodeGen/SimpleRegisterCoalescing.cpp
+++ b/llvm/lib/CodeGen/SimpleRegisterCoalescing.cpp
@@ -1767,8 +1767,18 @@ bool SimpleRegisterCoalescing::runOnMachineFunction(MachineFunction &fn) {
         if (!MO.isReg() || !MO.isKill()) continue;
         unsigned reg = MO.getReg();
         if (!reg || !li_->hasInterval(reg)) continue;
-        if (!li_->getInterval(reg).killedAt(DefIdx))
+        if (!li_->getInterval(reg).killedAt(DefIdx)) {
           MO.setIsKill(false);
+          continue;
+        }
+        // When leaving a kill flag on a physreg, check if any subregs should
+        // remain alive.
+        if (!TargetRegisterInfo::isPhysicalRegister(reg))
+          continue;
+        for (const unsigned *SR = tri_->getSubRegisters(reg);
+             unsigned S = *SR; ++SR)
+          if (li_->hasInterval(S) && li_->getInterval(S).liveAt(DefIdx))
+            MI->addRegisterDefined(S, tri_);
       }
     }
   }