This patch is an early implementation to extend debug ranges and provide multiple location support for debug variables. This work is based on the idea put forward in the mail thread: http://lists.cs.uiuc.edu/pipermail/llvmdev/2015-June/087109.html
A. Debug Range Extension: Currently, the debug ranges in LLVM end prematurely at the end of every basic block. This patch tries to extend them across basic blocks such that when two predecessors of a basic block have the same variable residing in the same location, a new debug value representing the variable and the location is added at the start of the current basic block.
Example: Consider the following partial code containing only DBG_VALUE instructions:
BB#3:
.
DBG_VALUE %EBX, %noreg, !"n", <!17>; line no:8
.
JMP_1 <BB#5>
BB#4:
.
DBG_VALUE %EBX, %noreg, !"n", <!17>; line no:8
.
BB#5: ; preds - BB#3, BB#4
DBG_VALUE %EBX, %noreg, !"n", <!17>; line no:8 <-- newly inserted
.
Here, BB#5 is a successor of both BB#3 and BB#4. Source variable "n" resides in %EBX on both paths. So a new DBG_VALUE instruction will be added at the start of BB#5 for "n" at location %EBX.
B. Multiple locations: Moved to http://reviews.llvm.org/D11986.
Just a general remark: Please follow
http://llvm.org/docs/CodingStandards.html#doxygen-use-in-documentation-comments
and use /// doxygen comments without \brief where possible.