In Thumb2, direct branches can be encoded as either a "short" conditional branch with a null predicate, or

as a "long" direct branch.  While the mnemonics are the same, they encode the branch offset differently, and
the Darwin assembler appears to prefer the "long" form for direct branches.  Thus, in the name of bitwise
equivalence, provide encoding and fixup support for it.

llvm-svn: 121710

1 files changed, 24 insertions, 2 deletions

diff --git a/llvm/lib/Target/ARM/ARMAsmBackend.cpp b/llvm/lib/Target/ARM/ARMAsmBackend.cpp
index ffa9307c9a7..cb0c54386ed 100644
--- a/llvm/lib/Target/ARM/ARMAsmBackend.cpp
+++ b/llvm/lib/Target/ARM/ARMAsmBackend.cpp
@@ -140,11 +140,32 @@ static unsigned adjustFixupValue(unsigned Kind, uint64_t Value) {
     // These values don't encode the low two bits since they're always zero.
     // Offset by 8 just as above.
     return 0xffffff & ((Value - 8) >> 2);
-  case ARM::fixup_t2_branch: {
+  case ARM::fixup_t2_uncondbranch: {
     Value = Value - 4;
     Value >>= 1; // Low bit is not encoded.
 
     uint32_t out = 0;
+    bool I =  Value & 0x800000;
+    bool J1 = Value & 0x400000;
+    bool J2 = Value & 0x200000;
+    J1 ^= I;
+    J2 ^= I;
+    
+    out |= I  << 26; // S bit
+    out |= !J1 << 13; // J1 bit
+    out |= !J2 << 11; // J2 bit
+    out |= (Value & 0x1FF800)  << 5; // imm6 field
+    out |= (Value & 0x0007FF);        // imm11 field
+    
+    uint64_t swapped = (out & 0xFFFF0000) >> 16;
+    swapped |= (out & 0x0000FFFF) << 16;
+    return swapped;
+  }
+  case ARM::fixup_t2_condbranch: {
+    Value = Value - 4;
+    Value >>= 1; // Low bit is not encoded.
+    
+    uint64_t out = 0;
     out |= (Value & 0x80000) << 7; // S bit
     out |= (Value & 0x40000) >> 7; // J2 bit
     out |= (Value & 0x20000) >> 4; // J1 bit
@@ -332,7 +353,8 @@ static unsigned getFixupKindNumBytes(unsigned Kind) {
 
   case FK_Data_4:
   case ARM::fixup_t2_ldst_pcrel_12:
-  case ARM::fixup_t2_branch:
+  case ARM::fixup_t2_condbranch:
+  case ARM::fixup_t2_uncondbranch:
   case ARM::fixup_t2_pcrel_10:
   case ARM::fixup_arm_thumb_bl:
   case ARM::fixup_arm_thumb_blx: