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
121 lines
2.0 KiB
LLVM
121 lines
2.0 KiB
LLVM
; RUN: llc -mtriple=i686-linux < %s | FileCheck %s
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; Don't rotate the loop if the number of fall through to exit is not larger
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; than the number of fall through to header.
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define void @no_rotate() {
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; CHECK-LABEL: no_rotate
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; CHECK: %entry
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; CHECK: %header
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; CHECK: %middle
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; CHECK: %latch1
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; CHECK: %latch2
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; CHECK: %end
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entry:
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br label %header
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header:
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%val1 = call i1 @foo()
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br i1 %val1, label %middle, label %end
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middle:
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%val2 = call i1 @foo()
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br i1 %val2, label %latch1, label %end
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latch1:
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%val3 = call i1 @foo()
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br i1 %val3, label %latch2, label %header
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latch2:
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%val4 = call i1 @foo()
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br label %header
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end:
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ret void
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}
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define void @do_rotate() {
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; CHECK-LABEL: do_rotate
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; CHECK: %entry
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; CHECK: %then
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; CHECK: %else
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; CHECK: %latch1
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; CHECK: %latch2
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; CHECK: %header
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; CHECK: %end
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entry:
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%val0 = call i1 @foo()
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br i1 %val0, label %then, label %else
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then:
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call void @a()
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br label %header
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else:
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call void @b()
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br label %header
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header:
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%val1 = call i1 @foo()
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br i1 %val1, label %latch1, label %end
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latch1:
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%val3 = call i1 @foo()
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br i1 %val3, label %latch2, label %header
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latch2:
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%val4 = call i1 @foo()
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br label %header
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end:
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ret void
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}
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; The loop structure is same as in @no_rotate, but the loop header's predecessor
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; doesn't fall through to it, so it should be rotated to get exit fall through.
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define void @do_rotate2() {
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; CHECK-LABEL: do_rotate2
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; CHECK: %entry
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; CHECK: %then
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; CHECK: %middle
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; CHECK: %latch1
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; CHECK: %latch2
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; CHECK: %header
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; CHECK: %exit
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entry:
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%val0 = call i1 @foo()
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br i1 %val0, label %then, label %header, !prof !1
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then:
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call void @a()
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br label %end
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header:
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%val1 = call i1 @foo()
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br i1 %val1, label %middle, label %exit
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middle:
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%val2 = call i1 @foo()
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br i1 %val2, label %latch1, label %exit
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latch1:
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%val3 = call i1 @foo()
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br i1 %val3, label %latch2, label %header
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latch2:
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%val4 = call i1 @foo()
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br label %header
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exit:
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call void @b()
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br label %end
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end:
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ret void
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}
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declare i1 @foo()
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declare void @a()
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declare void @b()
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!1 = !{!"branch_weights", i32 10, i32 1}
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