Changes

AMDGPU: Add run line to int_to_fp tests
This wasn't catching a regression on targets with legal i16 triggered in
a future commit.

[NFC][Test] Add a test to verify the DAGCombine of fma

[mlir][Linalg] Add a linalg.reshape op
Summary: This diff adds a new operation to linalg to allow reshaping of
an existing view into a new view in the same buffer at the same offset.
More specifically: The `linalg.reshape` op produces a new view whose
sizes are a reassociation of the original `view`. Depending on whether
or not the reassociated MemRefType is contiguous, the resulting memref
may require explicit alloc and copies.
A reassociation is defined as a continous grouping of dimensions and is 
represented with a affine map array attribute. In the future,
non-continous groupings may be allowed (i.e. permutations, reindexings
etc).
For now, it is assumed that either:
 1. a reassociation produces and consumes contiguous MemRefType or,
 2. the reshape op will be folded into its consumers (by changing the
shape
    of the computations). All other cases are undefined behavior and a
reshape op may not lower to LLVM if it cannot be proven statically that
it does not require alloc+copy.
A reshape may either collapse or expand dimensions, depending on the 
relationship between source and target memref ranks. The verification
rule is that the reassociation maps are applied to the memref with the
larger rank to obtain the memref with the smaller rank. In the case of a
dimension expansion, the reassociation maps can be interpreted as
inverse maps.
Examples:
```mlir
  // Dimension collapse (i, j) -> i' and k -> k'
  %1 = linalg.reshape %0 [(i, j, k) -> (i, j),
                          (i, j, k) -> (k)] :
    memref<?x?x?xf32, stride_spec> into memref<?x?xf32, stride_spec_2>
```
```mlir
  // Dimension expansion i -> (i', j') and (k) -> (k')
  %1 = linalg.reshape %0 [(i, j, k) -> (i, j),
                          (i, j, k) -> (k)] :
    memref<?x?xf32, stride_spec> into memref<?x?x?xf32, stride_spec_2>
```
The relevant invalid and roundtripping tests are added.
Reviewers: AlexEichenberger, ftynse, rriddle, asaadaldien, yangjunpro
Subscribers: kiszk, merge_guards_bot, mehdi_amini, jpienaar, burmako,
shauheen, antiagainst, arpith-jacob, mgester, lucyrfox, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D72168

AMDGPU/GlobalISel: Fix unused variable warning in release