Subzero: Add branch optimization.

tests_lit/llvm2ice_tests/branch-opt.ll

+; Tests the branch optimizations under O2 (against a lack of
+; optimizations under Om1).
+
+; RUN: %llvm2ice -O2 --verbose none %s \
+; RUN:   | llvm-mc -triple=i686-none-nacl -x86-asm-syntax=intel -filetype=obj \
+; RUN:   | llvm-objdump -d -symbolize -x86-asm-syntax=intel - \
+; RUN:   | FileCheck --check-prefix=O2 %s
+; RUN: %llvm2ice -Om1 --verbose none %s \
+; RUN:   | llvm-mc -triple=i686-none-nacl -x86-asm-syntax=intel -filetype=obj \
+; RUN:   | llvm-objdump -d -symbolize -x86-asm-syntax=intel - \
+; RUN:   | FileCheck --check-prefix=OM1 %s
+; RUN: %llvm2ice --verbose none %s | FileCheck --check-prefix=ERRORS %s
+; RUN: %llvm2iceinsts %s | %szdiff %s | FileCheck --check-prefix=DUMP %s
+; RUN: %llvm2iceinsts --pnacl %s | %szdiff %s \
+; RUN:                           | FileCheck --check-prefix=DUMP %s
+
+declare void @dummy()
+
+; An unconditional branch to the next block should be removed.
+define void @testUncondToNextBlock() {
+entry:
+  call void @dummy()
+  br label %next
+next:
+  call void @dummy()
+  ret void
+}
+; O2-LABEL: testUncondToNextBlock
+; O2: call
+; O2-NEXT: call
+
+; OM1-LABEL: testUncondToNextBlock
+; OM1: call
+; OM1-NEXT: jmp
+; OM1-NEXT: call
+
+; For a conditional branch with a fallthrough to the next block, the
+; fallthrough branch should be removed.
+define void @testCondFallthroughToNextBlock(i32 %arg) {
+entry:
+  %cmp = icmp sge i32 %arg, 123
+  br i1 %cmp, label %target, label %fallthrough
+fallthrough:
+  call void @dummy()
+  ret void
+target:
+  call void @dummy()
+  ret void
+}
+; O2-LABEL: testCondFallthroughToNextBlock
+; O2: cmp {{.*}}, 123
+; O2-NEXT: jge
+; O2-NEXT: call
+; O2: ret
+; O2: call
+; O2: ret
+
+; OM1-LABEL: testCondFallthroughToNextBlock
+; OM1: cmp {{.*}}, 123
+; OM1: jge
+; OM1: cmp
+; OM1: jne
+; OM1: jmp
+; OM1: call
+; OM1: ret
+; OM1: call
+; OM1: ret
+
+; For a conditional branch with the next block as the target and a
+; different block as the fallthrough, the branch condition should be
+; inverted, the fallthrough block changed to the target, and the
+; branch to the next block removed.
+define void @testCondTargetNextBlock(i32 %arg) {
+entry:
+  %cmp = icmp sge i32 %arg, 123
+  br i1 %cmp, label %fallthrough, label %target
+fallthrough:
+  call void @dummy()
+  ret void
+target:
+  call void @dummy()
+  ret void
+}
+; O2-LABEL: testCondTargetNextBlock
+; O2: cmp {{.*}}, 123
+; O2-NEXT: jl
+; O2-NEXT: call
+; O2: ret
+; O2: call
+; O2: ret
+
+; OM1-LABEL: testCondTargetNextBlock
+; OM1: cmp {{.*}}, 123
+; OM1: jge
+; OM1: cmp
+; OM1: jne
+; OM1: jmp
+; OM1: call
+; OM1: ret
+; OM1: call
+; OM1: ret
+
+; ERRORS-NOT: ICE translation error
+; DUMP-NOT: SZ