[llvm] r203757 - Phase 1 of refactoring the MachineRegisterInfo iterators to make them suitable

[Owen Anderson]

Hans,

On Mar 13, 2014, at 12:27 PM, Hans Wennborg <hans at chromium.org> wrote:

> On Thu, Mar 13, 2014 at 11:27 AM, Hans Wennborg <hans at chromium.org> wrote:
>> Hi Owen,
>> 
>> On Wed, Mar 12, 2014 at 11:02 PM, Owen Anderson <resistor at mac.com> wrote:
>>> Author: resistor
>>> Date: Thu Mar 13 01:02:25 2014
>>> New Revision: 203757
>>> 
>>> URL: http://llvm.org/viewvc/llvm-project?rev=203757&view=rev
>>> Log:
>>> Phase 1 of refactoring the MachineRegisterInfo iterators to make them suitable
>>> for use with C++11 range-based for-loops.
>>> 
>>> The gist of phase 1 is to remove the skipInstruction() and skipBundle()
>>> methods from these iterators, instead splitting each iterator into a version
>>> that walks operands, a version that walks instructions, and a version that
>>> walks bundles.  This has the result of making some "clever" loops in lib/CodeGen
>>> more verbose, but also makes their iterator invalidation characteristics much
>>> more obvious to the casual reader. (Making them concise again in the future is a
>>> good motivating case for a pre-incrementing range adapter!)
>>> 
>>> Phase 2 of this undertaking with consist of removing the getOperand() method,
>>> and changing operator*() of the operand-walker to return a MachineOperand&.  At
>>> that point, it should be possible to add range views for them that work as one
>>> might expect.
>> 
>> It seems this causes us to miscompile yasm on Windows (which we build
>> and use as part of Chromium).
>> 
>> I have no idea what's going on yet, but I'm working on a repro.
> 
> When compiling the attached .ii file like this:
> 
> clang "-cc1" "-triple" "i386-pc-win32" "-emit-obj"
> "-mrelocation-model" "static" "-mdisable-fp-elim" "-fmath-errno"
> "-masm-verbose" "-mconstructor-aliases" "-target-cpu" "pentium4"
> "-gline-tables-only"  "-O2"  "-mstackrealign" "-fno-rtti"
> "-fms-extensions" "-fms-compatibility" "-fmsc-version=1800"
> "-vectorize-loops" "-vectorize-slp" "-S" "-o"
> "d:\src\tmp\yasm.bitvect.asm" "-x" "c"
> "d:\src\tmp\yasm.bitvect.reduced.ii" -w
> 
> I get different output before and after your commit. Specifically in
> the _BitVector_from_Dec_static function, looking at the diff of asm
> before and after, it seems like the spill of %esi is missing, which
> could be causing the problem I see.
> 
> Do you have any idea of what could be happening here?

I’m getting errors from my clang when I try to compile your preprocessed source.  Is there any chance you can capture a bitcode file that exhibits the problem in llc?

—Owen
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