MIR Serialization: Change MIR syntax - use custom syntax for MBBs.


MIR Serialization: Change MIR syntax - use custom syntax for MBBs.

This commit modifies the way the machine basic blocks are serialized - now the
machine basic blocks are serialized using a custom syntax instead of relying on
YAML primitives. Instead of using YAML mappings to represent the individual
machine basic blocks in a machine function's body, the new syntax uses a single
YAML block scalar which contains all of the machine basic blocks and
instructions for that function.

This is an example of a function's body that uses the old syntax:

  - id: 0
    name: entry
      - '%eax = MOV32r0 implicit-def %eflags'
      - 'RETQ %eax'

The same body is now written like this:

body: |
    %eax = MOV32r0 implicit-def %eflags
    RETQ %eax

This syntax change is motivated by the fact that the bundled machine
instructions didn't map that well to the old syntax which was using a single
YAML sequence to store all of the machine instructions in a block. The bundled
machine instructions internally use flags like BundledPred and BundledSucc to
determine the bundles, and serializing them as MI flags using the old syntax
would have had a negative impact on the readability and the ease of editing
for MIR files. The new syntax allows me to serialize the bundled machine
instructions using a block construct without relying on the internal flags,
for example:

BUNDLE implicit-def dead %itstate, implicit-def %s1 ... {
   t2IT 1, 24, implicit-def %itstate
   %s1 = VMOVS killed %s0, 1, killed %cpsr, implicit killed %itstate

This commit also converts the MIR testcases to the new syntax. I developed
a script that can convert from the old syntax to the new one. I will post the
script on the llvm-commits mailing list in the thread for this commit.


arphamanAug 13 2015, 4:10 PM
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