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
37 lines
767 B
LLVM
37 lines
767 B
LLVM
; RUN: llc -mtriple=i686-linux < %s | FileCheck %s
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define i32 @bar(i32 %count) {
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; Test checks that basic block backedge2 is not moved before header,
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; because it can't reduce taken branches.
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; Later backedge1 and backedge2 is rotated before loop header.
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; CHECK-LABEL: bar
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; CHECK: %.entry
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; CHECK: %.header
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; CHECK: %.backedge1
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; CHECK: %.backedge2
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; CHECK: %.exit
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.entry:
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%c = shl nsw i32 %count, 2
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br label %.header
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.header:
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%val1 = call i32 @foo()
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%cond1 = icmp sgt i32 %val1, 1
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br i1 %cond1, label %.exit, label %.backedge1
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.backedge1:
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%val2 = call i32 @foo()
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%cond2 = icmp sgt i32 %val2, 1
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br i1 %cond2, label %.header, label %.backedge2
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.backedge2:
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%val3 = call i32 @foo()
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br label %.header
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.exit:
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ret i32 %c
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}
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declare i32 @foo()
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