[ARM] Check for addend before the Value is adjusted

As part of the checks, in some cases the Value is changed according
to if the Thumb bit is needed. This changes the value and can cause
the calcuation to check the range to falsely fail.

Moving the check before the Value is changed to ensure this cannot
occur.

Previously, tests existed that exploited the truncation of the
addend into a 16bit signed value, so these tests have been updated
to reflect the fact this is no longer allowed. It still tests the
instruction, but the expected outcome has been updated with new
values.

Author: Stylie777

llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp

@@ -447,6 +447,16 @@ unsigned ARMAsmBackend::adjustFixupValue(const MCAssembler &Asm,
                                          const MCSubtargetInfo* STI) const {
   unsigned Kind = Fixup.getKind();
 
+  // For MOVW/MOVT Instructions, the Fixup Value needs to be 16 bit aligned.
+  // If this is not the case, we should reject compilation.
+  if((Kind == ARM::fixup_arm_movw_lo16 || Kind == ARM::fixup_arm_movt_hi16 ||
+      Kind == ARM::fixup_t2_movw_lo16 || Kind == ARM::fixup_t2_movt_hi16) &&
+      (!(minIntN(16) <= static_cast<int64_t>(Value) &&
+    static_cast<int64_t>(Value) <= maxIntN(16)))) {
+    Ctx.reportError(Fixup.getLoc(), "Relocation Not In Range");
+    return 0;
+  }
+
   // MachO tries to make .o files that look vaguely pre-linked, so for MOVW/MOVT
   // and .word relocations they put the Thumb bit into the addend if possible.
   // Other relocation types don't want this bit though (branches couldn't encode
@@ -473,19 +483,11 @@ unsigned ARMAsmBackend::adjustFixupValue(const MCAssembler &Asm,
   case FK_SecRel_4:
     return Value;
   case ARM::fixup_arm_movt_hi16:
-    if(!(minIntN(16) <= static_cast<int64_t>(Value) && static_cast<int64_t>(Value) <= maxIntN(16))) {
-      Ctx.reportError(Fixup.getLoc(), "Relocation Not In Range");
-      return 0;
-    }
     assert(STI != nullptr);
     if (IsResolved || !STI->getTargetTriple().isOSBinFormatELF())
       Value >>= 16;
     [[fallthrough]];
   case ARM::fixup_arm_movw_lo16: {
-    if(!(minIntN(16) <= static_cast<int64_t>(Value) && static_cast<int64_t>(Value) <= maxIntN(16))) {
-      Ctx.reportError(Fixup.getLoc(), "Relocation Not In Range");
-      return 0;
-    }
     unsigned Hi4 = (Value & 0xF000) >> 12;
     unsigned Lo12 = Value & 0x0FFF;
     // inst{19-16} = Hi4;

llvm/test/MC/ARM/Windows/mov32t-range.s

@@ -21,7 +21,7 @@ truncation:
 
 	.section .rdata,"rd"
 .Lbuffer:
-	.zero 65536
+	.zero 32767
 .Lerange:
 	.asciz "-erange"
 
@@ -32,6 +32,6 @@ truncation:
 @ CHECK-RELOCATIONS:   }
 @ CHECK-RELOCATIONS: ]
 
-@ CHECK-ENCODING:      0: f240 0000
-@ CHECK-ENCODING-NEXT: 4: f2c0 0001
+@ CHECK-ENCODING:      0: f647 70ff
+@ CHECK-ENCODING-NEXT: 4: f2c0 0000
 

llvm/test/MC/MachO/ARM/thumb2-movw-fixup.s

@@ -11,7 +11,7 @@
 	movt	r2, :upper16:L1
   movw	r12, :lower16:L2
 	movt	r12, :upper16:L2
-  .space 70000
+  .space 16382
 
   .data
 L1: .long 0
@@ -30,7 +30,7 @@ L2: .long 0
 @ CHECK:       Section: __data (2)
 @ CHECK:     }
 @ CHECK:     Relocation {
-@ CHECK:       Offset: 0x1184
+@ CHECK:       Offset: 0x4012
 @ CHECK:       PCRel: 0
 @ CHECK:       Length: 3
 @ CHECK:       Type: ARM_RELOC_PAIR (1)
@@ -44,7 +44,7 @@ L2: .long 0
 @ CHECK:       Section: __data (2)
 @ CHECK:     }
 @ CHECK:     Relocation {
-@ CHECK:       Offset: 0x1
+@ CHECK:       Offset: 0x0
 @ CHECK:       PCRel: 0
 @ CHECK:       Length: 2
 @ CHECK:       Type: ARM_RELOC_PAIR (1)
@@ -58,7 +58,7 @@ L2: .long 0
 @ CHECK:       Section: __data (2)
 @ CHECK:     }
 @ CHECK:     Relocation {
-@ CHECK:       Offset: 0x1180
+@ CHECK:       Offset: 0x400E
 @ CHECK:       PCRel: 0
 @ CHECK:       Length: 3
 @ CHECK:       Type: ARM_RELOC_PAIR (1)
@@ -72,7 +72,7 @@ L2: .long 0
 @ CHECK:       Section: __data (2)
 @ CHECK:     }
 @ CHECK:     Relocation {
-@ CHECK:       Offset: 0x1
+@ CHECK:       Offset: 0x0
 @ CHECK:       PCRel: 0
 @ CHECK:       Length: 2
 @ CHECK:       Type: ARM_RELOC_PAIR (1)