Similar to 806761a7629df268c8aed49657aeccffa6bca449.
For IR files without a target triple, -mtriple= specifies the full
target triple while -march= merely sets the architecture part of the
default target triple, leaving a target triple which may not make sense,
e.g. amdgpu-apple-darwin.
Therefore, -march= is error-prone and not recommended for tests without
a target triple. The issue has been benign as we recognize
$unknown-apple-darwin as ELF instead of rejecting it outrightly.
This patch changes AMDGPU tests to not rely on the default
OS/environment components. Tests that need fixes are not changed:
```
LLVM :: CodeGen/AMDGPU/fabs.f64.ll
LLVM :: CodeGen/AMDGPU/fabs.ll
LLVM :: CodeGen/AMDGPU/floor.ll
LLVM :: CodeGen/AMDGPU/fneg-fabs.f64.ll
LLVM :: CodeGen/AMDGPU/fneg-fabs.ll
LLVM :: CodeGen/AMDGPU/r600-infinite-loop-bug-while-reorganizing-vector.ll
LLVM :: CodeGen/AMDGPU/schedule-if-2.ll
```
Fix bug where the code expects just a single MI, but a series of
bundled MIs need to be handled instead.
The semi-formed bundled are created by SplitKit for the case where
not all lanes are live (buildSingleSubRegCopy). Then the remat
kicks in, and since the values that are copied in the bundle do not
need to be preserved due to the remat (dead defs), all instructions
in the bundle should be marked as dead.
However, only the first one gets marked as dead, which causes the
verifier to complain later with error: "Live range continues after
dead def flag".
Differential Revision: https://reviews.llvm.org/D156999
