Prevent potential NOREX bug.

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

1 files changed, 11 insertions, 0 deletions

diff --git a/lib/Target/X86/X86RegisterInfo.cpp b/lib/Target/X86/X86RegisterInfo.cpp
index 23242e3edf..c1ac9f3431 100644
--- a/lib/Target/X86/X86RegisterInfo.cpp
+++ b/lib/Target/X86/X86RegisterInfo.cpp
@@ -246,6 +246,17 @@ X86RegisterInfo::getMatchingSuperRegClass(const TargetRegisterClass *A,
 
 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 {