ARM: do not relax Thumb1 -> Thumb2 if only Thumb1 is available.

After recognising that a certain narrow instruction might need a relocation to
be represented, we used to unconditionally relax it to a Thumb2 instruction to
permit this. Unfortunately, some CPUs (e.g. v6m) don't even have most Thumb2
instructions, so we end up emitting a completely invalid instruction.

Theoretically, ELF does have relocations for these situations; but they are
fairly unusable with such short ranges and the ABI document even says they're
documented "for completeness". So an error is probably better there too.

rdar://20391953

llvm-svn: 234195

lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp

@@ -153,18 +153,20 @@ void ARMAsmBackend::handleAssemblerFlag(MCAssemblerFlag Flag) {
 }
 } // end anonymous namespace
 
-static unsigned getRelaxedOpcode(unsigned Op) {
+unsigned ARMAsmBackend::getRelaxedOpcode(unsigned Op) const {
+  bool HasThumb2 = STI->getFeatureBits() & ARM::FeatureThumb2;
+
   switch (Op) {
   default:
     return Op;
   case ARM::tBcc:
-    return ARM::t2Bcc;
+    return HasThumb2 ? ARM::t2Bcc : Op;
   case ARM::tLDRpci:
-    return ARM::t2LDRpci;
+    return HasThumb2 ? ARM::t2LDRpci : Op;
   case ARM::tADR:
-    return ARM::t2ADR;
+    return HasThumb2 ? ARM::t2ADR : Op;
   case ARM::tB:
-    return ARM::t2B;
+    return HasThumb2 ? ARM::t2B : Op;
   case ARM::tCBZ:
     return ARM::tHINT;
   case ARM::tCBNZ:

lib/Target/ARM/MCTargetDesc/ARMAsmBackend.h

@@ -47,6 +47,8 @@ public:
   void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
                   uint64_t Value, bool IsPCRel) const override;
 
+  unsigned getRelaxedOpcode(unsigned Op) const;
+
   bool mayNeedRelaxation(const MCInst &Inst) const override;
 
   bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,

lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp

@@ -81,7 +81,9 @@ unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
   unsigned Type = 0;
   if (IsPCRel) {
     switch ((unsigned)Fixup.getKind()) {
-    default: llvm_unreachable("Unimplemented");
+    default:
+      report_fatal_error("unsupported relocation on symbol");
+      return ELF::R_ARM_NONE;
     case FK_Data_4:
       switch (Modifier) {
       default: llvm_unreachable("Unsupported Modifier");
@@ -147,7 +149,9 @@ unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
     }
   } else {
     switch ((unsigned)Fixup.getKind()) {
-    default: llvm_unreachable("invalid fixup kind!");
+    default:
+      report_fatal_error("unsupported relocation on symbol");
+      return ELF::R_ARM_NONE;
     case FK_Data_1:
       switch (Modifier) {
       default: llvm_unreachable("unsupported Modifier");

lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp

@@ -88,6 +88,7 @@ static bool getARMFixupKindMachOInfo(unsigned Kind, unsigned &RelocType,
   case ARM::fixup_arm_ldst_pcrel_12:
   case ARM::fixup_arm_pcrel_10:
   case ARM::fixup_arm_adr_pcrel_12:
+  case ARM::fixup_arm_thumb_br:
     return false;
 
     // Handle 24-bit branch kinds.
@@ -101,12 +102,6 @@ static bool getARMFixupKindMachOInfo(unsigned Kind, unsigned &RelocType,
     Log2Size = llvm::Log2_32(4);
     return true;
 
-    // Handle Thumb branches.
-  case ARM::fixup_arm_thumb_br:
-    RelocType = unsigned(MachO::ARM_THUMB_RELOC_BR22);
-    Log2Size = llvm::Log2_32(2);
-    return true;
-
   case ARM::fixup_t2_uncondbranch:
   case ARM::fixup_arm_thumb_bl:
   case ARM::fixup_arm_thumb_blx:

test/MC/ARM/thumb1-relax-adr.s

@@ -0,0 +1,9 @@
+@ RUN: not llvm-mc -triple thumbv6m-none-macho -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
+@ RUN: not llvm-mc -triple thumbv7m-none-macho -filetype=obj -o /dev/null %s 2>&1  | FileCheck --check-prefix=CHECK-ERROR %s
+@ RUN: not llvm-mc -triple thumbv7m-none-eabi -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
+
+        .global func1
+_func1:
+        adr r0, _func2
+@ CHECK-ERROR: unsupported relocation on symbol
+

test/MC/ARM/thumb1-relax-bcc.s

@@ -0,0 +1,12 @@
+@ RUN: not llvm-mc -triple thumbv6m-none-macho -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
+@ RUN: not llvm-mc -triple thumbv7m-none-macho -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
+@ RUN: llvm-mc -triple thumbv7m-none-eabi -filetype=obj -o %t %s
+@ RUN:    llvm-objdump -d -r -triple thumbv7m-none-eabi %t | FileCheck --check-prefix=CHECK-ELF %s
+
+        .global func1
+_func1:
+        bne _func2
+@ CHECK-ERROR: unsupported relocation on symbol
+
+@ CHECK-ELF: 7f f4 fe af        bne.w #-4
+@ CHECK-ELF-NEXT: R_ARM_THM_JUMP24 _func2

test/MC/ARM/thumb1-relax-br.s

@@ -0,0 +1,19 @@
+@ RUN: not llvm-mc -triple thumbv6m-none-macho -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
+@ RUN: llvm-mc -triple thumbv7m-none-macho -filetype=obj -o %t %s
+@ RUN:    llvm-objdump -d -r -triple thumbv7m-none-macho %t | FileCheck --check-prefix=CHECK-MACHO %s
+@ RUN: llvm-mc -triple thumbv7m-none-eabi -filetype=obj -o %t %s
+@ RUN:    llvm-objdump -d -r -triple thumbv7m-none-eabi %t | FileCheck --check-prefix=CHECK-ELF %s
+
+        .global func1
+_func1:
+        @ There is no MachO relocation for Thumb1's unconditional branch, so
+        @ this is unrepresentable. FIXME: I think ELF could represent this.
+        b _func2
+
+@ CHECK-ERROR: unsupported relocation on symbol
+
+@ CHECK-MACHO: ff f7 fe bf        b.w #-4
+@ CHECK-MACHO-NEXT: ARM_THUMB_RELOC_BR22
+
+@ CHECK-ELF: ff f7 fe bf        b.w #-4
+@ CHECK-ELF-NEXT: R_ARM_THM_JUMP24 _func2

test/MC/ARM/thumb1-relax-ldrlit.s

@@ -0,0 +1,9 @@
+@ RUN: not llvm-mc -triple thumbv6m-none-macho -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
+@ RUN: not llvm-mc -triple thumbv7m-none-macho -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
+@ RUN: not llvm-mc -triple thumbv7m-none-eabi -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
+
+        .global func1
+_func1:
+        ldr r0, _func2
+@ CHECK-ERROR: unsupported relocation on symbol
+