MIR Parser: Don't allow negative alignments for memory operands.

bool MIParser::parseAlignment(unsigned &Alignment) {

  assert(Token.is(MIToken::kw_align));

  lex();

  if (Token.isNot(MIToken::IntegerLiteral))

  if (Token.isNot(MIToken::IntegerLiteral) || Token.integerValue().isSigned())

    return error("expected an integer literal after 'align'");

  if (getUnsigned(Alignment))

    return true;

# RUN: not llc -march=x86-64 -start-after branch-folder -stop-after branch-folder -o /dev/null %s 2>&1 | FileCheck %s

--- |

  define void @memory_alignment(<8 x float>* %vec) {

  entry:

    %v = load <8 x float>, <8 x float>* %vec

    %v2 = insertelement <8 x float> %v, float 0.0, i32 4

    store <8 x float> %v2, <8 x float>* %vec

    ret void

  }

...

---

name:            memory_alignment

tracksRegLiveness: true

liveins:

  - { reg: '%rdi' }

body:

  - id:          0

    name:        entry

    liveins:     [ '%rdi' ]

    instructions:

# CHECK: [[@LINE+1]]:76: expected an integer literal after 'align'

      - '%xmm0 = MOVAPSrm %rdi, 1, _, 0, _ :: (load 16 from %ir.vec, align -32)'

      - '%xmm1 = MOVAPSrm %rdi, 1, _, 16, _ :: (load 16 from %ir.vec + 16, align 32)'

      - '%xmm2 = FsFLD0SS'

      - '%xmm1 = MOVSSrr killed %xmm1, killed %xmm2'

      - 'MOVAPSmr %rdi, 1, _, 0, _, killed %xmm0 :: (store 16 into %ir.vec, align 32)'

      - 'MOVAPSmr killed %rdi, 1, _, 16, _, killed %xmm1 :: (store 16 into %ir.vec + 16, align 32)'

      - RETQ

...