Fix register subclass handling in PPCInstrInfo::insertSelect

PPCInstrInfo::insertSelect and PPCInstrInfo::canInsertSelect were computing the
common subclass of the true and false inputs, and then selecting either the
32-bit or the 64-bit isel variant based on the result of calling
PPC::GPRCRegClass.hasSubClassEq(RC) and PPC::G8RCRegClass.hasSubClassEq(RC)
(where RC is the common subclass). Unfortunately, this is not quite right: if
we have something like this:

  %vreg8<def> = SELECT_CC_I8 %vreg4<kill>, %vreg7<kill>, %vreg6<kill>, 76;
    G8RC_and_G8RC_NOX0:%vreg8 CRRC:%vreg4 G8RC_NOX0:%vreg7,%vreg6

then the common subclass of G8RC_and_G8RC_NOX0 and G8RC_NOX0 is G8RC_NOX0, and
G8RC_NOX0 is not a subclass of G8RC (because it also contains the ZERO8
pseudo-register). As a result, we also need to check the common subclass
against GPRC_NOR0 and G8RC_NOX0 explicitly.

This had not been a problem for clients of insertSelect that called
canInsertSelect first (because it had a compensating mistake), but insertSelect
is also used by the PPC pseudo-instruction expander, and this error was causing
a problem in that context.

This problem was found by csmith.

llvm-svn: 186343

1 files changed, 10 insertions, 5 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
index 1ad879dd722..375daee59e9 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
@@ -448,7 +448,9 @@ bool PPCInstrInfo::canInsertSelect(const MachineBasicBlock &MBB,
 
   // isel is for regular integer GPRs only.
   if (!PPC::GPRCRegClass.hasSubClassEq(RC) &&
-      !PPC::G8RCRegClass.hasSubClassEq(RC))
+      !PPC::GPRC_NOR0RegClass.hasSubClassEq(RC) &&
+      !PPC::G8RCRegClass.hasSubClassEq(RC) &&
+      !PPC::G8RC_NOX0RegClass.hasSubClassEq(RC))
     return false;
 
   // FIXME: These numbers are for the A2, how well they work for other cores is
@@ -478,12 +480,15 @@ void PPCInstrInfo::insertSelect(MachineBasicBlock &MBB,
   const TargetRegisterClass *RC =
     RI.getCommonSubClass(MRI.getRegClass(TrueReg), MRI.getRegClass(FalseReg));
   assert(RC && "TrueReg and FalseReg must have overlapping register classes");
-  assert((PPC::GPRCRegClass.hasSubClassEq(RC) ||
-          PPC::G8RCRegClass.hasSubClassEq(RC)) &&
+
+  bool Is64Bit = PPC::G8RCRegClass.hasSubClassEq(RC) ||
+                 PPC::G8RC_NOX0RegClass.hasSubClassEq(RC);
+  assert((Is64Bit ||
+          PPC::GPRCRegClass.hasSubClassEq(RC) ||
+          PPC::GPRC_NOR0RegClass.hasSubClassEq(RC)) &&
          "isel is for regular integer GPRs only");
 
-  unsigned OpCode =
-    PPC::GPRCRegClass.hasSubClassEq(RC) ? PPC::ISEL : PPC::ISEL8;
+  unsigned OpCode = Is64Bit ? PPC::ISEL8 : PPC::ISEL;
   unsigned SelectPred = Cond[0].getImm();
 
   unsigned SubIdx;