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LoopIdiom: Recognize memmove loops.

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This turns loops like
  for (unsigned i = 0; i != n; ++i)
    p[i] = p[i+1];
into memmove, which has a highly optimized implementation in most libcs.

This was really easy with the new DependenceAnalysis :)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166875 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer
2012-10-27 14:25:51 +00:00
parent 96c8735e28
commit d11c5d08a5
2 changed files with 46 additions and 10 deletions
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test/Transforms/LoopIdiom/basic.ll
+22
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@@ -383,4 +383,26 @@ for.end: ; preds = %for.inc
}
@p = common global [1024 x i8] zeroinitializer, align 16
define void @test15(i32 %n) nounwind {
entry:
%cmp6 = icmp eq i32 %n, 0
br i1 %cmp6, label %for.end, label %for.body
for.body: ; preds = %entry, %for.body
%indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %entry ]
%indvars.iv.next = add i64 %indvars.iv, 1
%arrayidx = getelementptr inbounds [1024 x i8]* @p, i64 0, i64 %indvars.iv.next
%0 = load i8* %arrayidx, align 1
%arrayidx2 = getelementptr inbounds [1024 x i8]* @p, i64 0, i64 %indvars.iv
store i8 %0, i8* %arrayidx2, align 1
%lftr.wideiv = trunc i64 %indvars.iv.next to i32
%exitcond = icmp eq i32 %lftr.wideiv, %n
br i1 %exitcond, label %for.end, label %for.body
for.end: ; preds = %for.body, %entry
ret void
; CHECK: @test15
; CHECK: call void @llvm.memmove.p0i8.p0i8.i64(i8* getelementptr inbounds ([1024 x i8]* @p, i32 0, i32 0), i8* getelementptr inbounds ([1024 x i8]* @p, i64 0, i64 1),
}