[lld][Hexagon] Support predicated-add GOT_16_X mask lookup

When encountering an instruction like `if (p0) r0 = add(r0,##bar@GOT)`,
lld would fail with:
```
ld.lld: error: unrecognized instruction for 16_X type: 0x7400C000
```

This issue was encountered while building libreadline with clang 19.1.0.

Fixes: #111876

Author: androm3da

lld/ELF/Arch/Hexagon.cpp

@@ -181,11 +181,12 @@ static const InstructionMask r6[] = {
     {0xd7000000, 0x006020e0}, {0xd8000000, 0x006020e0},
     {0xdb000000, 0x006020e0}, {0xdf000000, 0x006020e0}};
 
+static constexpr uint32_t InstParsePacketEnd = 0x0000c000;
 static bool isDuplex(uint32_t insn) {
   // Duplex forms have a fixed mask and parse bits 15:14 are always
   // zero.  Non-duplex insns will always have at least one bit set in the
   // parse field.
-  return (0xC000 & insn) == 0;
+  return (InstParsePacketEnd & insn) == 0;
 }
 
 static uint32_t findMaskR6(uint32_t insn) {
@@ -216,6 +217,12 @@ static uint32_t findMaskR11(uint32_t insn) {
 }
 
 static uint32_t findMaskR16(uint32_t insn) {
+  if (isDuplex(insn))
+    return 0x03f00000;
+
+  // Clear the end-packet-parse bits:
+  insn = insn & ~InstParsePacketEnd;
+
   if ((0xff000000 & insn) == 0x48000000)
     return 0x061f20ff;
   if ((0xff000000 & insn) == 0x49000000)
@@ -225,8 +232,14 @@ static uint32_t findMaskR16(uint32_t insn) {
   if ((0xff000000 & insn) == 0xb0000000)
     return 0x0fe03fe0;
 
-  if (isDuplex(insn))
-    return 0x03f00000;
+  if ((0xff802000 & insn) == 0x74000000)
+    return 0x00001fe0;
+  if ((0xff802000 & insn) == 0x74002000)
+    return 0x00001fe0;
+  if ((0xff802000 & insn) == 0x74800000)
+    return 0x00001fe0;
+  if ((0xff802000 & insn) == 0x74802000)
+    return 0x00001fe0;
 
   for (InstructionMask i : r6)
     if ((0xff000000 & insn) == i.cmpMask)

lld/test/ELF/hexagon-shared.s

@@ -42,6 +42,13 @@ r0 = add(r1,##bar@GOT)
 { r0 = add(r0,##bar@GOT)
   memw(r0) = r2 }
 
+# R_HEX_GOT_16_X, pred add
+if (p0) r0 = add(r0,##bar@GOT)
+if (!p0) r0 = add(r0,##bar@GOT)
+{ p0 = cmp.gtu(r0, r1)
+  if (p0.new) r0 = add(r0,##bar@GOT) }
+{ p0 = cmp.gtu(r0, r1)
+  if (!p0.new) r0 = add(r0,##bar@GOT) }
 
 # foo is local so no plt will be generated
 foo:
@@ -78,12 +85,16 @@ pvar:
 # PLT-NEXT: r28 = memw(r14+#0) }
 # PLT-NEXT: jumpr r28 }
 
-# TEXT:  8c 00 01 00 0001008c
-# TEXT: { 	call 0x102d0 }
-# TEXT: if (p0) jump:nt 0x102d0
-# TEXT: r0 = #0 ; jump 0x102d0
+# TEXT:  bc 00 01 00 000100bc
+# TEXT: { 	call 0x10300 }
+# TEXT: if (p0) jump:nt 0x10300
+# TEXT: r0 = #0 ; jump 0x10300
 # TEXT: r0 = add(r1,##-65548)
 # TEXT: r0 = add(r0,##-65548); memw(r0+#0) = r2 }
+# TEXT: if (p0) r0 = add(r0,##-65548)
+# TEXT: if (!p0) r0 = add(r0,##-65548)
+# TEXT: if (p0.new) r0 = add(r0,##-65548)
+# TEXT: if (!p0.new) r0 = add(r0,##-65548)
 
 # GOT: .got:
 # GOT:  00 00 00 00 00000000 <unknown>