[jdc] 21-may-2010 To learn [LLVM] I made a wrapper got LLVM's C API. This wrapper is available at: http://github.com/jdc8/llvmtcl

**Building the wrapper**

The wrapper uses LLVM's C API as found in LLVM's header file `Core.h` in `include\llvm-c`. 

Requirements:

   * [LLVM] 2.7
   * [Tcl] 8.5 (most test have been done with Tcl HEAD)

There is a `Makefile` to build the extension;

   1. Edit the `Makefile` to specify the paths to your Tcl and LLVM. 
   1. Run `make` to build the extension. 
   1. You'll also have to add LLVM's lib path to `LD_LIBRARY_PATH`.
   1. Run `make test` to check it the extension is working

**Using the LLVM API**

Building a LLVM module and function:

======
lappend auto_path .
package require llvmtcl

namespace import llvmtcl::*

# Initialize the JIT
LLVMLinkInJIT
LLVMInitializeNativeTarget

# Create a module and builder
set m [LLVMModuleCreateWithName "testmodule"]
set bld [LLVMCreateBuilder]

# Create a plus10 function, taking one argument and adding 6 and 4 to it
set ft [LLVMFunctionType [LLVMInt32Type] [list [LLVMInt32Type]] 0]
set plus10 [LLVMAddFunction $m "plus10" $ft]

# Create constants
set c6 [LLVMConstInt [LLVMInt32Type] 6 0]
set c4 [LLVMConstInt [LLVMInt32Type] 4 0]

# Create the basic blocks
set entry [LLVMAppendBasicBlock $plus10 entry]

# Put arguments on the stack to avoid having to write select and/or phi nodes
LLVMPositionBuilderAtEnd $bld $entry
set arg0_1 [LLVMGetParam $plus10 0]
set arg0_2 [LLVMBuildAlloca $bld [LLVMInt32Type] arg0]
set arg0_3 [LLVMBuildStore $bld $arg0_1 $arg0_2]

# Do add 10 in two steps to see the optimizer @ work

# Add 6
set arg0_4 [LLVMBuildLoad $bld $arg0_2 "arg0"]
set add6 [LLVMBuildAdd $bld $arg0_4 $c6 "add6"]

# Add 4
set add4 [LLVMBuildAdd $bld $add6 $c4 "add4"]

# Set return
LLVMBuildRet $bld $add4

# Show input
puts "----- Input --------------------------------------------------"
puts [LLVMDumpModule $m]

# Verify the module
lassign [LLVMVerifyModule $m LLVMReturnStatusAction] rt msg
if {$rt} {
    error $msg
}
======

This results in the following LLVM bit code:

======
; ModuleID = 'testmodule'

define i32 @plus10(i32) {
entry:
  %arg0 = alloca i32                              ; <i32*> [#uses=2]
  store i32 %0, i32* %arg0
  %arg01 = load i32* %arg0                        ; <i32> [#uses=1]
  %add6 = add i32 %arg01, 6                       ; <i32> [#uses=1]
  %add4 = add i32 %add6, 4                        ; <i32> [#uses=1]
  ret i32 %add4
}
======

Now execute it:

======
# Execute
lassign [LLVMCreateJITCompilerForModule $m 0] rt EE msg
set i [LLVMCreateGenericValueOfInt [LLVMInt32Type] 4 0]
set res [LLVMRunFunction $EE $plus10 $i]
puts "plus10(4) = [LLVMGenericValueToInt $res 0]\n"
======

Now optimize the LLVM module:

======
# Optimize
set td [LLVMCreateTargetData ""]
LLVMSetDataLayout $m [LLVMCopyStringRepOfTargetData $td]
LLVMOptimizeFunction $m $plus10 3 $td
LLVMOptimizeModule $m 3 0 1 1 1 0 $td
======

Result of optimization:

======
; ModuleID = 'testmodule'
target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64"

define i32 @plus10(i32) readnone {
entry:
  %add4 = add i32 %0, 10                          ; <i32> [#uses=1]
  ret i32 %add4
}
======


**Transforming Tcl into LLVM bit code**

The LLVM wrapper has limited support for converting Tcl into LLVM bit code and is based on the output of [tcl::unsupported::disassemble]. Current (stringent) limitation are:

   * all variables are 32 bit integers (no strings, floats, lists, arrays, dicts, ...)
   * all proc's return a single 32 bit integer
   * all proc's must be know at convert time

(example still to be added)

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