AMDGPU: Fix dangling references introduced by r263982

Fixes Valgrind errors on the test cases that were reported as failing
by buildbots.

llvm-svn: 264000

AMDGPU: Coding style fixes

I meant to add these before committing r263982 as per the review,
but I forgot to squash.

llvm-svn: 263983

AMDGPU: Add SIWholeQuadMode pass

Summary:
Whole quad mode is already enabled for pixel shaders that compute
derivatives, but it must be suspended for instructions that cause a
shader to have side ef

AMDGPU: Add SIWholeQuadMode pass

Summary:
Whole quad mode is already enabled for pixel shaders that compute
derivatives, but it must be suspended for instructions that cause a
shader to have side effects (i.e. stores and atomics).

This pass addresses the issue by storing the real (initial) live mask
in a register, masking EXEC before instructions that require exact
execution and (re-)enabling WQM where required.

This pass is run before register coalescing so that we can use
machine SSA for analysis.

The changes in this patch expose a problem with the second machine
scheduling pass: target independent instructions like COPY implicitly
use EXEC when they operate on VGPRs, but this fact is not encoded in
the MIR. This can lead to miscompilation because instructions are
moved past changes to EXEC.

This patch fixes the problem by adding use-implicit operands to
target independent instructions. Some general codegen passes are
relaxed to work with such implicit use operands.

Reviewers: arsenm, tstellarAMD, mareko

Subscribers: MatzeB, arsenm, llvm-commits

Differential Revision: http://reviews.llvm.org/D18162

llvm-svn: 263982

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