Don't check liveness of unallocatable registers.

This includes registers like EFLAGS and ST0-ST7. We don't check for
liveness issues in the verifier and scavenger because registers will
never be allocated from these classes.

While in SSA form, we do care about the liveness of unallocatable
unreserved registers. Liveness of EFLAGS and ST0 neds to be correct for
MachineDCE and MachineSinking.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@136541 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 2 deletions

diff --git a/lib/CodeGen/MachineVerifier.cpp b/lib/CodeGen/MachineVerifier.cpp
index 8541d18ef3..f798c1346e 100644
--- a/lib/CodeGen/MachineVerifier.cpp
+++ b/lib/CodeGen/MachineVerifier.cpp
@@ -664,8 +664,15 @@ MachineVerifier::visitMachineOperand(const MachineOperand *MO, unsigned MONum) {
       // Use of a dead register.
       if (!regsLive.count(Reg)) {
         if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
-          // Reserved registers may be used even when 'dead'.
-          if (!isReserved(Reg))
+          // Reserved registers may be used even when 'dead', but allocatable
+          // registers can't.
+          // We track the liveness of unreserved, unallocatable registers while
+          // the machine function is still in SSA form. That lets us check for
+          // bad EFLAGS uses. After register allocation, the unallocatable
+          // registers are probably quite wrong. For example, the x87 ST0-ST7
+          // registers don't track liveness at all.
+          if (!isReserved(Reg) &&
+              (MRI->isSSA() || TRI->isInAllocatableClass(Reg)))
             report("Using an undefined physical register", MO, MONum);
         } else {
           BBInfo &MInfo = MBBInfoMap[MI->getParent()];