Add -reorder-basic-blocks option and fix nop insertion

tests_lit/llvm2ice_tests/reorder-basic-blocks.ll

+; Trivial smoke test of basic block reordering. Different random seeds should
+; generate different basic block layout.

[jvoung (off chromium), 2015/07/29 18:09:18]

Does this REQUIRES: allow_dump also?

[qining, 2015/07/29 23:04:40]

Yes, it requires. Added.

+
+; RUN: %p2i -i %s --filetype=asm --args -O2 -sz-seed=1 \
+; RUN: -reorder-basic-blocks -threads=0 \
+; RUN: | FileCheck %s --check-prefix=SEED1
+; RUN: %p2i -i %s --filetype=asm --args -O2 -sz-seed=2 \
+; RUN: -reorder-basic-blocks -threads=0 \
+; RUN: | FileCheck %s --check-prefix=SEED2
+
+define void @basic_block_reordering(i32 %foo, i32 %bar) {
+entry:
+  %r1 = icmp eq i32 %foo, %bar
+  br i1 %r1, label %BB1, label %BB2
+BB1:
+  %r2 = icmp sgt i32 %foo, %bar
+  br i1 %r2, label %BB3, label %BB4
+BB2:
+  %r3 = icmp slt i32 %foo, %bar
+  br i1 %r3, label %BB3, label %BB4
+BB3:
+  ret void
+BB4:
+  ret void
+
+
+; SEED1-LABEL: basic_block_reordering:
+; SEED1: .Lbasic_block_reordering$entry:
+; SEED1: .Lbasic_block_reordering$BB1:
+; SEED1: .Lbasic_block_reordering$BB2:
+; SEED1: .Lbasic_block_reordering$BB3:
+; SEED1: .Lbasic_block_reordering$BB4:
+
+; SEED2-LABEL: basic_block_reordering:
+; SEED2: .Lbasic_block_reordering$entry:
+; SEED2: .Lbasic_block_reordering$BB2:
+; SEED2: .Lbasic_block_reordering$BB1:
+; SEED2: .Lbasic_block_reordering$BB4:
+; SEED2: .Lbasic_block_reordering$BB3
+}
+