Commit Graph

6 Commits

Author SHA1 Message Date
Alexey Samsonov 8000e2734e Generate better location ranges for some register-described variables.
Don't terminate location ranges for register-described variables
at the end of machine basic block if this register is never modified
in the function body, except for the prologue and epilogue. Prologue
location is guessed by FrameSetup flags on MachineInstructions, while
epilogue location is deduced from debug locations of instructions
in the basic blocks ending with return instructions.

This patch is mostly targeted to fix non-trivial debug locations for
variables addressed via stack and frame pointers.

It is not really a generic fix. We can still produce poor debug info
for register-described variables if this register *is* modified somewhere
in the function, but in unrelated places. This might be the case for the debug
info in optimized binaries (e.g. for local variables in inlined functions).
LiveDebugVariables pass in CodeGen attempts to fix this problem by adjusting
DBG_VALUE instructions, but this pass is tied to greedy register allocator,
which is used in optimized builds only. Proper fix would likely involve
generalizing LiveDebugVariables to all register allocators. See more discussion
in http://reviews.llvm.org/D3933 review thread.

I'm proceeding with this patch to fix immediate severe problems and
important cases, e.g. fix completely broken debug info with AddressSanitizer
and fix PR19307 (missing debug info for by-value std::string arguments).

llvm-svn: 210492
2014-06-09 21:53:47 +00:00
Alexey Samsonov bb2990df58 Change representation of instruction ranges where variable is accessible.
Use more straightforward way to represent the set of instruction
ranges where the location of a user variable is defined - vector of pairs
of instructions (defining start/end of each range),
instead of a flattened vector of instructions where some instructions
are supposed to start the range, and the rest are supposed to "clobber" it.

Simplify the code which generates actual .debug_loc entries.

No functionality change.

llvm-svn: 209698
2014-05-27 23:09:50 +00:00
Alexey Samsonov f0e0cca0c7 Don't pre-populate the set of keys in the map with variable locations history.
Current implementation of calculateDbgValueHistory already creates the
keys in the expected order (user variables are listed in order of appearance),
and should do so later by contract.

No functionality change.

llvm-svn: 209690
2014-05-27 22:35:00 +00:00
Alexey Samsonov dfcaf9c8d8 Rewrite calculateDbgValueHistory to make it (hopefully) more transparent.
This change preserves the original algorithm of generating history
for user variables, but makes it more clear.

High-level description of algorithm:
Scan all the machine basic blocks and machine instructions in the order
they are emitted to the object file. Do the following:
1) If we see a DBG_VALUE instruction, add it to the history of the
corresponding user variable. Keep track of all user variables, whose
locations are described by a register.
2) If we see a regular instruction, look at all the registers it clobbers,
and terminate the location range for all variables described by these registers.
3) At the end of the basic block, terminate location ranges for all
user variables described by some register.

Although this change shouldn't be user-visible (the contents of .debug_loc section
should be the same), it changes some internal assumptions about the set
of instructions used to track the variable locations. Watching the bots.

llvm-svn: 209225
2014-05-20 18:34:54 +00:00
Alexey Samsonov f74bde6735 Convert more loops to range-based equivalents
llvm-svn: 207714
2014-04-30 22:17:38 +00:00
Alexey Samsonov 414b6fb170 Move logic for calculating DBG_VALUE history map into separate file/class.
Summary: No functionality change.

Test Plan: llvm regression test suite.

Reviewers: dblaikie

Reviewed By: dblaikie

Subscribers: echristo, llvm-commits

Differential Revision: http://reviews.llvm.org/D3573

llvm-svn: 207708
2014-04-30 21:34:11 +00:00