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6a55f3d913
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
122 lines
2.3 KiB
LLVM
122 lines
2.3 KiB
LLVM
; RUN: llc -mcpu=corei7 -mtriple=x86_64-linux < %s | FileCheck %s
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define void @foo() !prof !1 {
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; Test if a cold block in a loop will be placed at the end of the function
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; chain.
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;
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; CHECK-LABEL: foo:
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; CHECK: callq b
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; CHECK: callq c
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; CHECK: callq e
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; CHECK: callq f
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; CHECK: callq d
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entry:
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br label %header
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header:
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call void @b()
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%call = call zeroext i1 @a()
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br i1 %call, label %if.then, label %if.else, !prof !4
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if.then:
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call void @c()
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br label %if.end
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if.else:
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call void @d()
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br label %if.end
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if.end:
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call void @e()
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%call2 = call zeroext i1 @a()
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br i1 %call2, label %header, label %end, !prof !5
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end:
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call void @f()
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ret void
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}
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define void @nested_loop_0(i1 %flag) !prof !1 {
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; Test if a block that is cold in the inner loop but not cold in the outer loop
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; will merged to the outer loop chain.
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;
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; CHECK-LABEL: nested_loop_0:
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; CHECK: callq c
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; CHECK: callq d
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; CHECK: callq b
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; CHECK: callq e
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; CHECK: callq f
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entry:
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br label %header
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header:
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call void @b()
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%call4 = call zeroext i1 @a()
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br i1 %call4, label %header2, label %end
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header2:
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call void @c()
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%call = call zeroext i1 @a()
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br i1 %call, label %if.then, label %if.else, !prof !2
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if.then:
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call void @d()
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%call3 = call zeroext i1 @a()
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br i1 %call3, label %header2, label %header, !prof !3
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if.else:
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call void @e()
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br i1 %flag, label %header2, label %header, !prof !3
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end:
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call void @f()
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ret void
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}
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define void @nested_loop_1() !prof !1 {
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; Test if a cold block in an inner loop will be placed at the end of the
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; function chain.
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;
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; CHECK-LABEL: nested_loop_1:
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; CHECK: callq b
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; CHECK: callq c
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; CHECK: callq e
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; CHECK: callq d
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entry:
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br label %header
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header:
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call void @b()
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br label %header2
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header2:
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call void @c()
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%call = call zeroext i1 @a()
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br i1 %call, label %end, label %if.else, !prof !4
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if.else:
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call void @d()
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%call2 = call zeroext i1 @a()
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br i1 %call2, label %header2, label %header, !prof !5
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end:
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call void @e()
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ret void
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}
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declare zeroext i1 @a()
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declare void @b()
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declare void @c()
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declare void @d()
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declare void @e()
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declare void @f()
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!1 = !{!"function_entry_count", i64 1}
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!2 = !{!"branch_weights", i32 100, i32 1}
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!3 = !{!"branch_weights", i32 1, i32 10}
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!4 = !{!"branch_weights", i32 1000, i32 1}
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!5 = !{!"branch_weights", i32 100, i32 1}
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