llvm-project/llvm/test/CodeGen/X86/loop-blocks.ll

; RUN: llc < %s -march=x86-64 -mtriple=x86_64-unknown-linux-gnu -asm-verbose=false | FileCheck %s

; These tests check for loop branching structure, and that the loop align
; directive is placed in the expected place.

; CodeGen should insert a branch into the middle of the loop in
; order to avoid a branch within the loop.

; CHECK: simple:
;      CHECK:   jmp   .LBB0_1
; CHECK-NEXT:   align
; CHECK-NEXT: .LBB0_2:
; CHECK-NEXT:   callq loop_latch
; CHECK-NEXT: .LBB0_1:
; CHECK-NEXT:   callq loop_header

define void @simple() nounwind {
entry:
  br label %loop

loop:
  call void @loop_header()
  %t0 = tail call i32 @get()
  %t1 = icmp slt i32 %t0, 0
  br i1 %t1, label %done, label %bb

bb:
  call void @loop_latch()
  br label %loop

done:
  call void @exit()
  ret void
}

; CodeGen should move block_a to the top of the loop so that it
; falls through into the loop, avoiding a branch within the loop.

; CHECK: slightly_more_involved:
;      CHECK:   jmp .LBB1_1
; CHECK-NEXT:   align
; CHECK-NEXT: .LBB1_4:
; CHECK-NEXT:   callq bar99
; CHECK-NEXT: .LBB1_1:
; CHECK-NEXT:   callq body

define void @slightly_more_involved() nounwind {
entry:
  br label %loop

loop:
  call void @body()
  %t0 = call i32 @get()
  %t1 = icmp slt i32 %t0, 2
  br i1 %t1, label %block_a, label %bb

bb:
  %t2 = call i32 @get()
  %t3 = icmp slt i32 %t2, 99
  br i1 %t3, label %exit, label %loop

block_a:
  call void @bar99()
  br label %loop

exit:
  call void @exit()
  ret void
}

; Same as slightly_more_involved, but block_a is now a CFG diamond with
; fallthrough edges which should be preserved.
; "callq block_a_merge_func" is tail duped.

; CHECK: yet_more_involved:
;      CHECK:   jmp .LBB2_1
; CHECK-NEXT:   align
; CHECK-NEXT: .LBB2_4:
; CHECK-NEXT:   callq bar99
; CHECK-NEXT:   callq get
; CHECK-NEXT:   cmpl $2999, %eax
; CHECK-NEXT:   jle .LBB2_5
; CHECK-NEXT:   callq block_a_false_func
; CHECK-NEXT:   callq block_a_merge_func
; CHECK-NEXT:   jmp .LBB2_1
; CHECK-NEXT: .LBB2_5:
; CHECK-NEXT:   callq block_a_true_func
; CHECK-NEXT:   callq block_a_merge_func
; CHECK-NEXT: .LBB2_1:
; CHECK-NEXT:   callq body

define void @yet_more_involved() nounwind {
entry:
  br label %loop

loop:
  call void @body()
  %t0 = call i32 @get()
  %t1 = icmp slt i32 %t0, 2
  br i1 %t1, label %block_a, label %bb

bb:
  %t2 = call i32 @get()
  %t3 = icmp slt i32 %t2, 99
  br i1 %t3, label %exit, label %loop

block_a:
  call void @bar99()
  %z0 = call i32 @get()
  %z1 = icmp slt i32 %z0, 3000
  br i1 %z1, label %block_a_true, label %block_a_false

block_a_true:
  call void @block_a_true_func()
  br label %block_a_merge

block_a_false:
  call void @block_a_false_func()
  br label %block_a_merge

block_a_merge:
  call void @block_a_merge_func()
  br label %loop

exit:
  call void @exit()
  ret void
}

; CodeGen should move the CFG islands that are part of the loop but don't
; conveniently fit anywhere so that they are at least contiguous with the
; loop.

; CHECK: cfg_islands:
;      CHECK:   jmp     .LBB3_1
; CHECK-NEXT:   align
; CHECK-NEXT: .LBB3_7:
; CHECK-NEXT:   callq   bar100
; CHECK-NEXT:   jmp     .LBB3_1
; CHECK-NEXT: .LBB3_8:
; CHECK-NEXT:   callq   bar101
; CHECK-NEXT:   jmp     .LBB3_1
; CHECK-NEXT: .LBB3_9:
; CHECK-NEXT:   callq   bar102
; CHECK-NEXT:   jmp     .LBB3_1
; CHECK-NEXT: .LBB3_5:
; CHECK-NEXT:   callq   loop_latch
; CHECK-NEXT: .LBB3_1:
; CHECK-NEXT:   callq   loop_header

define void @cfg_islands() nounwind {
entry:
  br label %loop

loop:
  call void @loop_header()
  %t0 = call i32 @get()
  %t1 = icmp slt i32 %t0, 100
  br i1 %t1, label %block100, label %bb

bb:
  %t2 = call i32 @get()
  %t3 = icmp slt i32 %t2, 101
  br i1 %t3, label %block101, label %bb1

bb1:
  %t4 = call i32 @get()
  %t5 = icmp slt i32 %t4, 102
  br i1 %t5, label %block102, label %bb2

bb2:
  %t6 = call i32 @get()
  %t7 = icmp slt i32 %t6, 103
  br i1 %t7, label %exit, label %bb3

bb3:
  call void @loop_latch()
  br label %loop

exit:
  call void @exit()
  ret void

block100:
  call void @bar100()
  br label %loop

block101:
  call void @bar101()
  br label %loop

block102:
  call void @bar102()
  br label %loop
}

declare void @bar99() nounwind
declare void @bar100() nounwind
declare void @bar101() nounwind
declare void @bar102() nounwind
declare void @body() nounwind
declare void @exit() nounwind
declare void @loop_header() nounwind
declare void @loop_latch() nounwind
declare i32 @get() nounwind
declare void @block_a_true_func() nounwind
declare void @block_a_false_func() nounwind
declare void @block_a_merge_func() nounwind