d2210af332
Current findBestLoopTop can find and move one kind of block to top, a latch block has one successor. Another common case is:
* a latch block
* it has two successors, one is loop header, another is exit
* it has more than one predecessors
If it is below one of its predecessors P, only P can fall through to it, all other predecessors need a jump to it, and another conditional jump to loop header. If it is moved before loop header, all its predecessors jump to it, then fall through to loop header. So all its predecessors except P can reduce one taken branch.
Differential Revision: https://reviews.llvm.org/D43256
llvm-svn: 363471
284 lines
5.9 KiB
LLVM
284 lines
5.9 KiB
LLVM
; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -asm-verbose=false | FileCheck %s
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; These tests check for loop branching structure, and that the loop align
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; directive is placed in the expected place.
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; CodeGen should insert a branch into the middle of the loop in
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; order to avoid a branch within the loop.
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; CHECK-LABEL: simple:
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; CHECK: align
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; CHECK-NEXT: .LBB0_1:
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; CHECK-NEXT: callq loop_header
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; CHECK: js .LBB0_3
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; CHECK-NEXT: callq loop_latch
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; CHECK-NEXT: jmp .LBB0_1
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; CHECK-NEXT: .LBB0_3:
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; CHECK-NEXT: callq exit
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define void @simple() nounwind {
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entry:
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br label %loop
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loop:
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call void @loop_header()
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%t0 = tail call i32 @get()
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%t1 = icmp slt i32 %t0, 0
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br i1 %t1, label %done, label %bb
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bb:
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call void @loop_latch()
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br label %loop
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done:
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call void @exit()
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ret void
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}
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; CodeGen should move block_a to the top of the loop so that it
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; falls through into the loop, avoiding a branch within the loop.
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; CHECK-LABEL: slightly_more_involved:
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; CHECK: jmp .LBB1_1
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; CHECK-NEXT: align
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; CHECK-NEXT: .LBB1_4:
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; CHECK-NEXT: callq bar99
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; CHECK-NEXT: .LBB1_1:
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; CHECK-NEXT: callq body
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define void @slightly_more_involved() nounwind {
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entry:
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br label %loop
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loop:
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call void @body()
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%t0 = call i32 @get()
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%t1 = icmp slt i32 %t0, 2
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br i1 %t1, label %block_a, label %bb
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bb:
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%t2 = call i32 @get()
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%t3 = icmp slt i32 %t2, 99
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br i1 %t3, label %exit, label %loop
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block_a:
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call void @bar99()
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br label %loop
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exit:
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call void @exit()
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ret void
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}
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; Same as slightly_more_involved, but block_a is now a CFG diamond with
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; fallthrough edges which should be preserved.
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; "callq block_a_merge_func" is tail duped.
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; CHECK-LABEL: yet_more_involved:
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; CHECK: jmp .LBB2_1
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; CHECK-NEXT: align
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; CHECK: .LBB2_1:
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; CHECK-NEXT: callq body
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; CHECK-NEXT: callq get
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; CHECK-NEXT: cmpl $2, %eax
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; CHECK-NEXT: jge .LBB2_2
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; CHECK-NEXT: callq bar99
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; CHECK-NEXT: callq get
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; CHECK-NEXT: cmpl $2999, %eax
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; CHECK-NEXT: jg .LBB2_6
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; CHECK-NEXT: callq block_a_true_func
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; CHECK-NEXT: callq block_a_merge_func
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; CHECK-NEXT: jmp .LBB2_1
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; CHECK-NEXT: align
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; CHECK-NEXT: .LBB2_6:
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; CHECK-NEXT: callq block_a_false_func
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; CHECK-NEXT: callq block_a_merge_func
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; CHECK-NEXT: jmp .LBB2_1
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define void @yet_more_involved() nounwind {
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entry:
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br label %loop
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loop:
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call void @body()
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%t0 = call i32 @get()
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%t1 = icmp slt i32 %t0, 2
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br i1 %t1, label %block_a, label %bb
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bb:
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%t2 = call i32 @get()
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%t3 = icmp slt i32 %t2, 99
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br i1 %t3, label %exit, label %loop
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block_a:
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call void @bar99()
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%z0 = call i32 @get()
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%z1 = icmp slt i32 %z0, 3000
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br i1 %z1, label %block_a_true, label %block_a_false
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block_a_true:
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call void @block_a_true_func()
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br label %block_a_merge
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block_a_false:
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call void @block_a_false_func()
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br label %block_a_merge
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block_a_merge:
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call void @block_a_merge_func()
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br label %loop
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exit:
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call void @exit()
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ret void
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}
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; CodeGen should move the CFG islands that are part of the loop but don't
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; conveniently fit anywhere so that they are at least contiguous with the
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; loop.
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; CHECK-LABEL: cfg_islands:
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; CHECK: jmp .LBB3_1
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; CHECK-NEXT: align
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; CHECK-NEXT: .LBB3_7:
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; CHECK-NEXT: callq bar100
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; CHECK-NEXT: .LBB3_1:
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; CHECK-NEXT: callq loop_header
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; CHECK: jl .LBB3_7
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; CHECK: jge .LBB3_3
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; CHECK-NEXT: callq bar101
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; CHECK-NEXT: jmp .LBB3_1
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; CHECK-NEXT: align
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; CHECK-NEXT: .LBB3_3:
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; CHECK: jge .LBB3_4
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; CHECK-NEXT: callq bar102
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; CHECK-NEXT: jmp .LBB3_1
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; CHECK-NEXT: .LBB3_4:
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; CHECK: jl .LBB3_6
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; CHECK-NEXT: callq loop_latch
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; CHECK-NEXT: jmp .LBB3_1
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; CHECK-NEXT: .LBB3_6:
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define void @cfg_islands() nounwind {
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entry:
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br label %loop
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loop:
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call void @loop_header()
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%t0 = call i32 @get()
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%t1 = icmp slt i32 %t0, 100
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br i1 %t1, label %block100, label %bb
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bb:
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%t2 = call i32 @get()
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%t3 = icmp slt i32 %t2, 101
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br i1 %t3, label %block101, label %bb1
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bb1:
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%t4 = call i32 @get()
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%t5 = icmp slt i32 %t4, 102
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br i1 %t5, label %block102, label %bb2
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bb2:
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%t6 = call i32 @get()
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%t7 = icmp slt i32 %t6, 103
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br i1 %t7, label %exit, label %bb3
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bb3:
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call void @loop_latch()
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br label %loop
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exit:
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call void @exit()
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ret void
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block100:
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call void @bar100()
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br label %loop
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block101:
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call void @bar101()
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br label %loop
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block102:
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call void @bar102()
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br label %loop
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}
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; CHECK-LABEL: check_minsize:
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; CHECK-NOT: align
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; CHECK: .LBB4_1:
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; CHECK-NEXT: callq loop_header
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; CHECK: callq loop_latch
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; CHECK: .LBB4_3:
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; CHECK: callq exit
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define void @check_minsize() minsize nounwind {
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entry:
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br label %loop
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loop:
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call void @loop_header()
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%t0 = tail call i32 @get()
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%t1 = icmp slt i32 %t0, 0
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br i1 %t1, label %done, label %bb
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bb:
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call void @loop_latch()
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br label %loop
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done:
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call void @exit()
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ret void
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}
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; This is exactly the same function as slightly_more_involved.
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; The difference is that when optimising for size, we do not want
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; to see this reordering.
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; CHECK-LABEL: slightly_more_involved_2:
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; CHECK-NOT: jmp .LBB5_1
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; CHECK: .LBB5_1:
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; CHECK-NEXT: callq body
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define void @slightly_more_involved_2() #0 {
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entry:
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br label %loop
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loop:
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call void @body()
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%t0 = call i32 @get()
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%t1 = icmp slt i32 %t0, 2
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br i1 %t1, label %block_a, label %bb
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bb:
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%t2 = call i32 @get()
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%t3 = icmp slt i32 %t2, 99
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br i1 %t3, label %exit, label %loop
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block_a:
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call void @bar99()
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br label %loop
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exit:
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call void @exit()
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ret void
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}
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attributes #0 = { minsize norecurse nounwind optsize readnone uwtable }
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declare void @bar99() nounwind
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declare void @bar100() nounwind
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declare void @bar101() nounwind
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declare void @bar102() nounwind
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declare void @body() nounwind
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declare void @exit() nounwind
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declare void @loop_header() nounwind
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declare void @loop_latch() nounwind
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declare i32 @get() nounwind
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declare void @block_a_true_func() nounwind
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declare void @block_a_false_func() nounwind
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declare void @block_a_merge_func() nounwind
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