[mips] For PIC code convert unconditional jump to unconditional branch

[atanasyan]

Summary

Unconditional branch uses relative addressing which is the right choice in case of position independent code.

This is a fix for the bug:
https://dmz-portal.mips.com/bugz/show_bug.cgi?id=2445

[sdardis]

LGTM with the nits addressed.

lib/Target/Mips/AsmParser/MipsAsmParser.cpp

1791

Nit: This comment should be before the "if ((Inst.getOpcode() == ..".

test/MC/Mips/expansion-j-sym-pic.s

2–8

Tiny nit: the check prefix should be MIPS.

10–17

Tiny nit: the check prefix should MM.

lib/Target/Mips/AsmParser/MipsAsmParser.cpp

switch (Opcode) {
           return Error(IDLoc, "expected immediate operand kind");
         Imm = Opnd.getImm();
         if (!isInt<10>(Imm))
           return Error(IDLoc, "immediate operand value out of range");
         break;
     }
   }
 
+  if ((Inst.getOpcode() == Mips::J || Inst.getOpcode() == Mips::J_MM) &&
+      inPicMode()) {
+    // For PIC code convert unconditional jump to unconditional branch.
+    MCInst BInst;
+    BInst.setOpcode(inMicroMipsMode() ? Mips::BEQ_MM : Mips::BEQ);
+    BInst.addOperand(MCOperand::createReg(Mips::ZERO));
+    BInst.addOperand(MCOperand::createReg(Mips::ZERO));
+    BInst.addOperand(Inst.getOperand(0));
+    Inst = BInst;
+  }
+
   // This expansion is not in a function called by tryExpandInstruction()
   // because the pseudo-instruction doesn't have a distinct opcode.
   if ((Inst.getOpcode() == Mips::JAL || Inst.getOpcode() == Mips::JAL_MM) &&
       inPicMode()) {
     warnIfNoMacro(IDLoc);
 
     const MCExpr *JalExpr = Inst.getOperand(0).getExpr();
 

test/MC/Mips/expansion-j-sym-pic.s

+# RUN: llvm-mc %s -arch=mips -mcpu=mips32 -show-encoding |\
+# RUN:   FileCheck %s -check-prefix=NORMAL
+
+# RUN: llvm-mc %s -arch=mips -mcpu=mips64 -target-abi n32 -show-encoding |\
+# RUN:   FileCheck %s -check-prefix=NORMAL
+
+# RUN: llvm-mc %s -arch=mips64 -mcpu=mips64 -target-abi n64 -show-encoding |\
+# RUN:   FileCheck %s -check-prefix=NORMAL
+
+# RUN: llvm-mc %s -arch=mips -mcpu=mips32 -mattr=micromips -show-encoding |\
+# RUN:   FileCheck %s -check-prefix=MICRO
+
+# RUN: llvm-mc %s -arch=mips64 -mcpu=mips64 -target-abi n32 -mattr=micromips -show-encoding |\
+# RUN:   FileCheck %s -check-prefix=MICRO
+
+# RUN: llvm-mc %s -arch=mips64 -mcpu=mips64 -target-abi n64 -mattr=micromips -show-encoding |\
+# RUN:   FileCheck %s -check-prefix=MICRO
+
+# Repeat the tests using ELF output.
+
+# RUN: llvm-mc %s -arch=mips -mcpu=mips32 -filetype=obj | \
+# RUN:   llvm-objdump -d -r - | FileCheck %s -check-prefixes=ELF-O32
+# RUN: llvm-mc %s -arch=mips64 -mcpu=mips64 -target-abi n32 -filetype=obj | \
+# RUN:   llvm-objdump -d -r - | FileCheck %s -check-prefixes=ELF-NXX
+# RUN: llvm-mc %s -arch=mips64 -mcpu=mips64 -target-abi n64 -filetype=obj | \
+# RUN:   llvm-objdump -d -r - | FileCheck %s -check-prefixes=ELF-NXX
+
+  .weak weak_label
+
+  .text
+  .option pic2
+
+  .ent local_label
+local_label:
+  .frame  $sp, 0, $ra
+  .set noreorder
+
+  j local_label
+  nop
+
+# NORMAL: b      local_label      # encoding: [0x10,0x00,A,A]
+# NORMAL:                         #   fixup A - offset: 0, value: local_label-4, kind: fixup_Mips_PC16
+
+# MICRO:  b      local_label      # encoding: [0x94,0x00,A,A]
+# MICRO:                          #   fixup A - offset: 0, value: local_label, kind: fixup_MICROMIPS_PC16_S1
+
+# ELF-O32:      10 00 ff ff     b       0
+
+# ELF-NXX:      10 00 ff ff     b       0
+
+  j weak_label
+  nop
+
+# NORMAL: b      weak_label       # encoding: [0x10,0x00,A,A]
+# NORMAL:                         #   fixup A - offset: 0, value: weak_label-4, kind: fixup_Mips_PC16
+
+# MICRO:  b      weak_label       # encoding: [0x94,0x00,A,A]
+# MICRO:                          #   fixup A - offset: 0, value: weak_label, kind: fixup_MICROMIPS_PC16_S1
+
+# ELF-O32:      10 00 ff ff     b       0
+# ELF-O32-NEXT:                 R_MIPS_PC16  weak_label
+
+# ELF-NXX:      10 00 00 00     b       4
+# ELF-NXX-NEXT:                 R_MIPS_PC16/R_MIPS_NONE/R_MIPS_NONE  weak_label
+
+  j global_label
+  nop
+
+# NORMAL: b      global_label     # encoding: [0x10,0x00,A,A]
+# NORMAL:                         #   fixup A - offset: 0, value: global_label-4, kind: fixup_Mips_PC16
+
+# MICRO:  b      global_label     # encoding: [0x94,0x00,A,A]
+# MICRO:                          #   fixup A - offset: 0, value: global_label, kind: fixup_MICROMIPS_PC16_S1
+
+# ELF-O32:      10 00 ff ff     b       0
+# ELF-O32-NEXT:         00000010:  R_MIPS_PC16  global_label
+
+# ELF-NXX:      10 00 00 00     b       4
+# ELF-NXX-NEXT:                 R_MIPS_PC16/R_MIPS_NONE/R_MIPS_NONE  global_label
+
+  j .text
+  nop
+
+# NORMAL: b      .text            # encoding: [0x10,0x00,A,A]
+# NORMAL:                         #   fixup A - offset: 0, value: .text-4, kind: fixup_Mips_PC16
+
+# MICRO:  b      .text            # encoding: [0x94,0x00,A,A]
+# MICRO:                          #   fixup A - offset: 0, value: .text, kind: fixup_MICROMIPS_PC16_S1
+
+# ELF-O32:      10 00 ff ff     b       0
+# ELF-O32-NEXT:         00000018:  R_MIPS_PC16  .text
+
+# ELF-NXX:      10 00 00 00     b       4
+# ELF-NXX-NEXT:                 R_MIPS_PC16/R_MIPS_NONE/R_MIPS_NONE  .text
+
+  j 1f
+  nop
+
+# NORMAL: b      {{.*}}tmp0{{.*}} # encoding: [0x10,0x00,A,A]
+# NORMAL:                         #   fixup A - offset: 0, value: {{.*}}tmp0{{.*}}-4, kind: fixup_Mips_PC16
+
+# MICRO:  b      {{.*}}tmp0{{.*}} # encoding: [0x94,0x00,A,A]
+# MICRO:                          #   fixup A - offset: 0, value: {{.*}}tmp0{{.*}}, kind: fixup_MICROMIPS_PC16_S1
+
+# ELF-O32:      10 00 00 04     b       20 <local_label+0x34>
+
+# ELF-NXX:      10 00 00 04     b       20 <local_label+0x34>
+
+  .local forward_local
+  j forward_local
+  nop
+
+# NORMAL: b      forward_local    # encoding: [0x10,0x00,A,A]
+# NORMAL:                         #   fixup A - offset: 0, value: forward_local-4, kind: fixup_Mips_PC16
+
+# MICRO:  b      forward_local    # encoding: [0x94,0x00,A,A]
+# MICRO:                          #   fixup A - offset: 0, value: forward_local, kind: fixup_MICROMIPS_PC16_S1
+
+# ELF-O32:      10 00 00 04     b       20 <forward_local>
+
+# ELF-NXX:      10 00 00 04     b       20 <forward_local>
+
+  j 0x4
+
+# NORMAL: b      4                # encoding: [0x10,0x00,0x00,0x01]
+
+# MICRO:  b      4                # encoding: [0x94,0x00,0x00,0x02]
+
+# ELF-O32:      10 00 00 01     b       8
+
+# ELF-NXX:      10 00 00 01     b       8
+
+  .end local_label
+
+1:
+  nop
+  nop
+forward_local:
+