[AArch64] Switch magic numbers to library functions in fixup

Using masks and bounds that are magic numbers means that defects
in bounds checking and offset masking are subtle and hard to
detect. https://reviews.llvm.org/D152841 is an example of this
type of defect. Switching to clearly readable library functions
makes defects less obfuscated.

Differential Revision: https://reviews.llvm.org/D152843

llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp

@@ -181,14 +181,14 @@ static uint64_t adjustFixupValue(const MCFixup &Fixup, const MCValue &Target,
     if (TheTriple.isOSBinFormatCOFF() && !IsResolved)
       Value &= 0xfff;
     // Unsigned 12-bit immediate
-    if (Value >= 0x1000)
+    if (!isUInt<12>(Value))
       Ctx.reportError(Fixup.getLoc(), "fixup value out of range");
     return Value;
   case AArch64::fixup_aarch64_ldst_imm12_scale2:
     if (TheTriple.isOSBinFormatCOFF() && !IsResolved)
       Value &= 0xfff;
     // Unsigned 12-bit immediate which gets multiplied by 2
-    if (Value >= 0x2000)
+    if (!isUInt<13>(Value))
       Ctx.reportError(Fixup.getLoc(), "fixup value out of range");
     if (Value & 0x1)
       Ctx.reportError(Fixup.getLoc(), "fixup must be 2-byte aligned");
@@ -197,7 +197,7 @@ static uint64_t adjustFixupValue(const MCFixup &Fixup, const MCValue &Target,
     if (TheTriple.isOSBinFormatCOFF() && !IsResolved)
       Value &= 0xfff;
     // Unsigned 12-bit immediate which gets multiplied by 4
-    if (Value >= 0x4000)
+    if (!isUInt<14>(Value))
       Ctx.reportError(Fixup.getLoc(), "fixup value out of range");
     if (Value & 0x3)
       Ctx.reportError(Fixup.getLoc(), "fixup must be 4-byte aligned");
@@ -206,7 +206,7 @@ static uint64_t adjustFixupValue(const MCFixup &Fixup, const MCValue &Target,
     if (TheTriple.isOSBinFormatCOFF() && !IsResolved)
       Value &= 0xfff;
     // Unsigned 12-bit immediate which gets multiplied by 8
-    if (Value >= 0x8000)
+    if (!isUInt<15>(Value))
       Ctx.reportError(Fixup.getLoc(), "fixup value out of range");
     if (Value & 0x7)
       Ctx.reportError(Fixup.getLoc(), "fixup must be 8-byte aligned");
@@ -215,7 +215,7 @@ static uint64_t adjustFixupValue(const MCFixup &Fixup, const MCValue &Target,
     if (TheTriple.isOSBinFormatCOFF() && !IsResolved)
       Value &= 0xfff;
     // Unsigned 12-bit immediate which gets multiplied by 16
-    if (Value >= 0x10000)
+    if (!isUInt<16>(Value))
       Ctx.reportError(Fixup.getLoc(), "fixup value out of range");
     if (Value & 0xf)
       Ctx.reportError(Fixup.getLoc(), "fixup must be 16-byte aligned");
@@ -306,7 +306,7 @@ static uint64_t adjustFixupValue(const MCFixup &Fixup, const MCValue &Target,
   }
   case AArch64::fixup_aarch64_pcrel_branch14:
     // Signed 16-bit immediate
-    if (SignedValue > 32767 || SignedValue < -32768)
+    if (!isInt<16>(SignedValue))
       Ctx.reportError(Fixup.getLoc(), "fixup value out of range");
     // Low two bits are not encoded (4-byte alignment assumed).
     if (Value & 0x3)
@@ -315,7 +315,7 @@ static uint64_t adjustFixupValue(const MCFixup &Fixup, const MCValue &Target,
   case AArch64::fixup_aarch64_pcrel_branch26:
   case AArch64::fixup_aarch64_pcrel_call26:
     // Signed 28-bit immediate
-    if (SignedValue > 134217727 || SignedValue < -134217728)
+    if (!isInt<28>(SignedValue))
       Ctx.reportError(Fixup.getLoc(), "fixup value out of range");
     // Low two bits are not encoded (4-byte alignment assumed).
     if (Value & 0x3)