[mips][FastISel] Specify which types we handle for integer extension.

[vkalintiris]

Summary

Perform integer extension only when the destination type is one of
i8, i16 & i32 and when the source type is i1, i8 or i16. For other
combinations we fall back to SelectionDAG.

[vkalintiris]

This patch is part of the revision D6765 which I will not be able to commit for the next few days. However, because this fixes some failures in our out-of-tree MIPS buildbots, I created a new review request that contains only the fix.

[dsanders]

LGTM

[dsanders]

Please say which test-suite test it fixes in the commit message though.

lib/Target/Mips/MipsFastISel.cpp

case MVT::i16:
     emitInst(Mips::ANDi, DestReg).addReg(SrcReg).addImm(0xffff);
     break;
   }
   return true;
 }
 
 bool MipsFastISel::emitIntExt(MVT SrcVT, unsigned SrcReg, MVT DestVT,
                               unsigned DestReg, bool IsZExt) {
+  // FastISel does not have plumbing to deal with extensions where the SrcVT or
+  // DestVT are odd things, so test to make sure that they are both types we can
+  // handle (i1/i8/i16/i32 for SrcVT and i8/i16/i32/i64 for DestVT), otherwise
+  // bail out to SelectionDAG.
+  if (((DestVT != MVT::i8) && (DestVT != MVT::i16) && (DestVT != MVT::i32)) ||
+      ((SrcVT != MVT::i1) && (SrcVT != MVT::i8) && (SrcVT != MVT::i16)))
+    return false;
   if (IsZExt)
     return emitIntZExt(SrcVT, SrcReg, DestVT, DestReg);
   return emitIntSExt(SrcVT, SrcReg, DestVT, DestReg);
 }
 
 unsigned MipsFastISel::emitIntExt(MVT SrcVT, unsigned SrcReg, MVT DestVT,
                                   bool isZExt) {
   unsigned DestReg = createResultReg(&Mips::GPR32RegClass);