Initially, the "bench" entries of the test suite used a "xtime" utility
developed in-house and not publically available.

This commit adds a version of "xtime" written in OCaml (tools/xtime.ml)
and updates the "bench" entries of the test/*/Makefile to use it.

The temporary variables introduced by SimplLocals reuse the same
integer identifiers as the local variables they come from.  This commit
ensures that these variables are printed as "$var", where "var"
is the original variable name, instead of "$NNN" as before.

The "$NNN" form is retained for temporary variables that do not
correspond to a source-level local variable, such as the temporary
variables introduced by SimplExpr.

This commit should make no difference for "ccomp -dclight", because
the Clight that is printed is the Clight version 1 produced by
SimplExpr, where every temporary is fresh and does not correspond
to a source-level local variable.

This commit does change the output of "clightgen -dclight", because
the Clight that is printed is the Clight version 2 produced by
SimplLocals.  The printed Clight is much more legible thanks to
the more meaningful temporary variable names.

The Clight output of clightgen is Clight version 2, after SimplLocals
conversion, where function parameters are temporary variables, not
variables.

This commit makes sure the function parameters are printed as
temporary variables and not as variables.  In passing, it
generalizes the Clight pretty-printer so that it can print
both Clight version 1 and Clight version 2.

Closes: #314

The json export prints formatted json, which takes a lot of
additional time, however the result is only consumed by other tools
and not meant for human reading.

This commit implements several small changes in order to speedup
the json export:

* Removal of usage of the Format Module
* Replacing `fprintf` calls by calls to function that print
  directly, such as `output_string`, etc.
* Replacing list of all instruction names by a set of all
  instructions

"omega" fails in Coq 8.7, but not in 8.8 and later.

Support target architecture AArch64 (ARMv8 in 64-bit mode)

Unused-variables is disabled by default.

The argument is of type Tlong, not Tint.
This caused spurious errors in RTLtyping.

Also: in AArch64/PrintOp.ml, print Cmaskl{zero,notzero} with "&l"
to distinguish them from Cmask{zero,notzero}.

These instructions are generated by __builtin_memcpy.

Some changes were not correctly propagated to all architectures.

Since the ppc64 has 64 bit registers it is okay to have a 64 bit
constant result.

* Added semantic for byte swap builtins

The `__builtin_bswap`, `__builtin_bswap16`,  `__builtin_bswap32`, `__builtin_bswap64` builtin function are now standard builtin functions with a defined semantics.

The semantics  is given in terms of the decode/encode functions used for the memory model.

* Added bswap64 expansion to PowerPC 32 bits.

* Added bswap64 expansion for ARM.

With special emphasis on the use of the AArch64 fmov #imm instruction.

This commit adds a back-end for the AArch64 architecture, namely ARMv8
in 64-bit mode.

Syntax is "pat ?? bexpr => action".
The whole case is selected only when "pat" matches and then "bexpr"
evaluates to "true".

This is a variant of exec_straight where it is allowed to take zero steps.
In other words, exec_straight0 is the "star" relation, while exec_straight
is the "plus" relation.
In the end we need "plus" relations in simulation diagrams, to show
the absence of stuttering.  But the "star" relation exec_straight0 is
useful to reason about code fragments that are always preceded or
followed by at least one instruction.

Should simplify reasoning over Boolean equalities.

Just ensure sign_ext 0 x = zero.  This simplifies some statements and proofs.

There was a misunderstanding on the asm syntax for 3-operand instructions
such as vfmadd132: when the Intel manual reads
     vfmadd132 res, arg2, arg3
the corresponding GNU asm syntax is
     vfmadd132 arg3, arg2, res
but not
     vfmadd132 arg2, arg3, res

Closes: #188

The "undeclared-scope" warning fires when we use a "notation" scope
before having declared it.  This is a good thing, except that
the "Declare Scope" vernacular that declares a scope was introduced
in Coq 8.10 and is not available in earlier versions.

Hence there is no way to avoid triggering the warning yet remain
compatible with pre-8.10 Coq versions.

This commit silences the warning.  It will have to revisited when
Coq 8.10 is the oldest version of Coq we support in CompCert.

"Hint Resolve foo." becomes "Hint Resolve foo : core", or
"Local Hint Resolve foo : core".

PG now uses the _Coqproject file and finds relevant paths there.

There was a misunderstanding on the asm syntax for 3-operand instructions
such as vfmadd132: when the Intel manual reads
     vfmadd132 res, arg2, arg3
the corresponding GNU asm syntax is
     vfmadd132 arg3, arg2, res
but not
     vfmadd132 arg2, arg3, res

Closes: #188

The "undeclared-scope" warning fires when we use a "notation" scope
before having declared it.  This is a good thing, except that
the "Declare Scope" vernacular that declares a scope was introduced
in Coq 8.10 and is not available in earlier versions.

Hence there is no way to avoid triggering the warning yet remain
compatible with pre-8.10 Coq versions.

This commit silences the warning.  It will have to revisited when
Coq 8.10 is the oldest version of Coq we support in CompCert.

"Hint Resolve foo." becomes "Hint Resolve foo : core", or
"Local Hint Resolve foo : core".

PG now uses the _Coqproject file and finds relevant paths there.