Add R_HEX_8_X relocation support

[sidneym]

Summary

Another relocation with a non-uniform relocation mask, but just 3 in this case.

[ruiu]

LGTM

lld/trunk/ELF/Arch/Hexagon.cpp

for (InstructionMask I : R6)
     if ((0xff000000 & Insn) == I.CmpMask)
       return I.RelocMask;
 
   error("unrecognized instruction for R_HEX_6 relocation: 0x" +
         utohexstr(Insn));
   return 0;
 }
 
+static uint32_t findMaskR8(uint32_t Insn) {
+  if ((0xff000000 & Insn) == 0xde000000)
+    return 0x00e020e8;
+  if ((0xff000000 & Insn) == 0x3c000000)
+    return 0x0000207f;
+  return 0x00001fe0;
+}
+
 static void or32le(uint8_t *P, int32_t V) { write32le(P, read32le(P) | V); }
 
 void Hexagon::relocateOne(uint8_t *Loc, RelType Type, uint64_t Val) const {
   switch (Type) {
   case R_HEX_NONE:
     break;
   case R_HEX_6_PCREL_X:
   case R_HEX_6_X:
     or32le(Loc, applyMask(findMaskR6(read32le(Loc)), Val));
     break;
+  case R_HEX_8_X:
+    or32le(Loc, applyMask(findMaskR8(read32le(Loc)), Val));
+    break;
   case R_HEX_12_X:
     or32le(Loc, applyMask(0x000007e0, Val));
     break;
   case R_HEX_32_6_X:
     or32le(Loc, applyMask(0x0fff3fff, Val >> 6));
     break;
   case R_HEX_B15_PCREL:
     or32le(Loc, applyMask(0x00df20fe, Val >> 2));

lld/trunk/test/ELF/hexagon.s

 
 # R_HEX_HI16
 r0.h = #HI(_start)
 # CHECK: r0.h = #1
 
 # R_HEX_LO16
 r0.l = #LO(_start)
 # CHECK: r0.l = #4096
+
+# R_HEX_8_X has 3 relocation mask variations
+#0xde000000
+r0=sub(##_start,asl(r1,#4))
+# CHECK: de00c406     r0 = sub(##69632,asl(r0,#4)) }
+
+#0x3c000000
+memw(r0+#0) = ##_start
+# CHECK: 3c40c000     memw(r0+#0) = ##69632 }
+
+# The rest:
+r1:0=combine(r2,##_start);
+# CHECK: 7302e000     r1:0 = combine(r2,##69632) }