A GR8_NOREX virtual register is created when extrating a sub_8bit_hi
sub-register:
%vreg2<def> = COPY %vreg1:sub_8bit_hi; GR8_NOREX:%vreg2 %GR64_ABCD:%vreg1
TEST8ri_NOREX %vreg2, 1, %EFLAGS<imp-def>; GR8_NOREX:%vreg2
If such a live range is ever split, its register class must not be
inflated to GR8. The sub-register copy can only target GR8_NOREX.
I dont have a test case for this theoretical bug.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141500
91177308-0d34-0410-b5e6-
96231b3b80d8
const TargetRegisterClass*
X86RegisterInfo::getLargestLegalSuperClass(const TargetRegisterClass *RC) const{
+ // Don't allow super-classes of GR8_NOREX. This class is only used after
+ // extrating sub_8bit_hi sub-registers. The H sub-registers cannot be copied
+ // to the full GR8 register class in 64-bit mode, so we cannot allow the
+ // reigster class inflation.
+ //
+ // The GR8_NOREX class is always used in a way that won't be constrained to a
+ // sub-class, so sub-classes like GR8_ABCD_L are allowed to expand to the
+ // full GR8 class.
+ if (RC == X86::GR8_NOREXRegisterClass)
+ return RC;
+
const TargetRegisterClass *Super = RC;
TargetRegisterClass::sc_iterator I = RC->getSuperClasses();
do {