[PATCH] D128798: [lld-macho] Emit REBASE_OPCODE_ADD_ADDR_IMM_SCALED if possible

[Daniel Bertalan via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rG8d29f0fdb9c6: [lld-macho] Emit REBASE_OPCODE_ADD_ADDR_IMM_SCALED if possible (authored by BertalanD).
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Changed prior to commit:
  https://reviews.llvm.org/D128798?vs=441098&id=441150#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D128798/new/

https://reviews.llvm.org/D128798

Files:
  lld/MachO/SyntheticSections.cpp
  lld/test/MachO/rebase-opcodes.s


Index: lld/test/MachO/rebase-opcodes.s
===================================================================
--- /dev/null
+++ lld/test/MachO/rebase-opcodes.s
@@ -0,0 +1,45 @@
+# REQUIRES: x86
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
+# RUN: %lld -dylib %t.o -o %t.dylib
+# RUN: obj2yaml %t.dylib | FileCheck %s
+
+## Test that:
+## 1/ Consecutive rebases are encoded as REBASE_OPCODE_DO_REBASE_IMM_TIMES.
+## 2/ Gaps smaller than 15 words are encoded as REBASE_OPCODE_ADD_ADDR_IMM_SCALED.
+## 3/ Gaps larger than that become REBASE_OPCODE_ADD_ADDR_ULEB.
+## FIXME: The last rebase could be transformed into a REBASE_OPCODE_DO_REBASE_ADD_ADDR_ULEB.
+
+# CHECK: RebaseOpcodes:
+# CHECK-NEXT: Opcode:          REBASE_OPCODE_SET_TYPE_IMM
+# CHECK-NEXT: Imm:             1
+# CHECK-NEXT: Opcode:          REBASE_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB
+# CHECK-NEXT: Imm:             1
+# CHECK-NEXT: ExtraData:       [ 0x0 ]
+# CHECK-NEXT: Opcode:          REBASE_OPCODE_DO_REBASE_IMM_TIMES
+# CHECK-NEXT: Imm:             1
+# CHECK-NEXT: Opcode:          REBASE_OPCODE_ADD_ADDR_IMM_SCALED
+# CHECK-NEXT: Imm:             14
+# CHECK-NEXT: Opcode:          REBASE_OPCODE_DO_REBASE_IMM_TIMES
+# CHECK-NEXT: Imm:             3
+# CHECK-NEXT: Opcode:          REBASE_OPCODE_ADD_ADDR_ULEB
+# CHECK-NEXT: Imm:             0
+# CHECK-NEXT: ExtraData:       [ 0x78 ]
+# CHECK-NEXT: Opcode:          REBASE_OPCODE_DO_REBASE_IMM_TIMES
+# CHECK-NEXT: Imm:             1
+# CHECK-NEXT: Opcode:          REBASE_OPCODE_DONE
+# CHECK-NEXT: Imm:             0
+
+
+.text
+.globl _foo
+_foo:
+
+.data
+.quad _foo
+.space 112
+.quad _foo
+.quad _foo
+.quad _foo
+.space 120
+.quad _foo
Index: lld/MachO/SyntheticSections.cpp
===================================================================
--- lld/MachO/SyntheticSections.cpp
+++ lld/MachO/SyntheticSections.cpp
@@ -202,8 +202,18 @@
       lastRebase.offset = offset;
     } else {
       assert(lastRebase.offset != offset);
-      os << static_cast<uint8_t>(REBASE_OPCODE_ADD_ADDR_ULEB);
-      encodeULEB128(offset - lastRebase.offset, os);
+      uint64_t delta = offset - lastRebase.offset;
+      // For unknown reasons, ld64 checks if the scaled offset is strictly less
+      // than REBASE_IMMEDIATE_MASK instead of allowing equality. We match this
+      // behavior as a precaution.
+      if ((delta % target->wordSize == 0) &&
+          (delta / target->wordSize < REBASE_IMMEDIATE_MASK)) {
+        os << static_cast<uint8_t>(REBASE_OPCODE_ADD_ADDR_IMM_SCALED |
+                                   (delta / target->wordSize));
+      } else {
+        os << static_cast<uint8_t>(REBASE_OPCODE_ADD_ADDR_ULEB);
+        encodeULEB128(delta, os);
+      }
       lastRebase.offset = offset;
     }
   }


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