+//
+// A LOH describes a sequence of instructions that may be optimized by the
+// linker.
+// This same sequence cannot be optimized by the compiler because some of
+// the information will be known at link time.
+// For instance, consider the following sequence:
+// L1: adrp xA, sym@PAGE
+// L2: add xB, xA, sym@PAGEOFF
+// L3: ldr xC, [xB, #imm]
+// This sequence can be turned into:
+// A literal load if sym@PAGE + sym@PAGEOFF + #imm - address(L3) is < 1MB:
+// L3: ldr xC, sym+#imm
+// It may also be turned into either the following more efficient
+// code sequences:
+// - If sym@PAGEOFF + #imm fits the encoding space of L3.
+// L1: adrp xA, sym@PAGE
+// L3: ldr xC, [xB, sym@PAGEOFF + #imm]
+// - If sym@PAGE + sym@PAGEOFF - address(L1) < 1MB:
+// L1: adr xA, sym
+// L3: ldr xC, [xB, #imm]
+//
+// To be valid a LOH must meet all the requirements needed by all the related
+// possible linker transformations.
+// For instance, using the running example, the constraints to emit
+// ".loh AdrpAddLdr" are:
+// - L1, L2, and L3 instructions are of the expected type, i.e.,
+// respectively ADRP, ADD (immediate), and LD.
+// - The result of L1 is used only by L2.
+// - The register argument (xA) used in the ADD instruction is defined
+// only by L1.
+// - The result of L2 is used only by L3.
+// - The base address (xB) in L3 is defined only L2.
+// - The ADRP in L1 and the ADD in L2 must reference the same symbol using
+// @PAGE/@PAGEOFF with no additional constants
+//
+// Currently supported LOHs are: