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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
39 lines
1.0 KiB
LLVM
39 lines
1.0 KiB
LLVM
; Test BRCTH.
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; RUN: llc < %s -verify-machineinstrs -mtriple=s390x-linux-gnu -mcpu=z196 \
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; RUN: -no-integrated-as -disable-block-placement | FileCheck %s
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; Test a loop that should be converted into dbr form and then use BRCTH.
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define void @f2(i32 *%src, i32 *%dest) {
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; CHECK-LABEL: f2:
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; CHECK: blah [[REG:%r[0-5]]]
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; CHECK: [[LABEL:\.[^:]*]]:{{.*}} %loop
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; CHECK: brcth [[REG]], [[LABEL]]
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; CHECK: br %r14
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entry:
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; Force upper bound into a high register in order to encourage the
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; register allocator to use a high register for the count variable.
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%top = call i32 asm sideeffect "blah $0", "=h"()
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br label %loop
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loop:
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%count = phi i32 [ 0, %entry ], [ %next, %loop.next ]
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%next = add i32 %count, 1
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%val = load volatile i32, i32 *%src
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%cmp = icmp eq i32 %val, 0
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br i1 %cmp, label %loop.next, label %loop.store
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loop.store:
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%add = add i32 %val, 1
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store volatile i32 %add, i32 *%dest
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br label %loop.next
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loop.next:
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%cont = icmp ne i32 %next, %top
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br i1 %cont, label %loop, label %exit
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exit:
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ret void
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}
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