[lld] [lld][Hexagon] Fix predicated-add GOT_16_X mask lookup (PR #111896)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lld

Author: Brian Cain (androm3da)

<details>
<summary>Changes</summary>

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

---
Full diff: https://github.com/llvm/llvm-project/pull/111896.diff


2 Files Affected:

- (modified) lld/ELF/Arch/Hexagon.cpp (+16-3) 
- (modified) lld/test/ELF/hexagon-shared.s (+15-4) 


``````````diff
diff --git a/lld/ELF/Arch/Hexagon.cpp b/lld/ELF/Arch/Hexagon.cpp
index 5d2477cc800651..e3d2a2e688d2fd 100644
--- a/lld/ELF/Arch/Hexagon.cpp
+++ b/lld/ELF/Arch/Hexagon.cpp
@@ -181,11 +181,12 @@ static const InstructionMask r6[] = {
     {0xd7000000, 0x006020e0}, {0xd8000000, 0x006020e0},
     {0xdb000000, 0x006020e0}, {0xdf000000, 0x006020e0}};
 
+static uint32_t INST_PARSE_PACKET_END = 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 (INST_PARSE_PACKET_END & 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 & ~INST_PARSE_PACKET_END;
+
   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)
diff --git a/lld/test/ELF/hexagon-shared.s b/lld/test/ELF/hexagon-shared.s
index 747822039e839a..01f72865847056 100644
--- a/lld/test/ELF/hexagon-shared.s
+++ b/lld/test/ELF/hexagon-shared.s
@@ -42,6 +42,13 @@ r0 = add(r1,##bar at GOT)
 { r0 = add(r0,##bar at GOT)
   memw(r0) = r2 }
 
+# R_HEX_GOT_16_X, pred add
+if (p0) r0 = add(r0,##bar at GOT)
+if (!p0) r0 = add(r0,##bar at GOT)
+{ p0 = cmp.gtu(r0, r1)
+  if (p0.new) r0 = add(r0,##bar at GOT) }
+{ p0 = cmp.gtu(r0, r1)
+  if (!p0.new) r0 = add(r0,##bar at 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>

``````````

</details>


https://github.com/llvm/llvm-project/pull/111896