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08a0e8f8db
Don't classify idiv/udiv as a reduction operation. Integer division is lossy.
For example : (1 / 2) * 4 != 4/2.
Example:
int a[] = { 2, 5, 2, 2}
int x = 80;
for()
x /= a[i];
Scalar:
x /= 2 // = 40
x /= 5 // = 8
x /= 2 // = 4
x /= 2 // = 2
Vectorized:
<80, 1> / <2,5> //= <40,0>
<40, 0> / <2,2> //= <20,0>
20*0 = 0
radar://13640654
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179381 91177308-0d34-0410-b5e6-96231b3b80d8
25 lines
799 B
LLVM
25 lines
799 B
LLVM
; RUN: opt -loop-vectorize -force-vector-width=2 -force-vector-unroll=1 -S < %s | FileCheck %s
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@a = common global [128 x i32] zeroinitializer, align 16
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;; Must not vectorize division reduction. Division is lossy.
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define i32 @g() {
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entry:
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br label %for.body
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for.body:
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; CHECK: @g
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; CHECK-NOT: sdiv <2 x i32>
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%indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
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%r.05 = phi i32 [ 80, %entry ], [ %div, %for.body ]
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%arrayidx = getelementptr inbounds [128 x i32]* @a, i64 0, i64 %indvars.iv
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%0 = load i32* %arrayidx, align 4
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%div = sdiv i32 %r.05, %0
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%indvars.iv.next = add i64 %indvars.iv, 1
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%lftr.wideiv = trunc i64 %indvars.iv.next to i32
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%exitcond = icmp eq i32 %lftr.wideiv, 1024
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br i1 %exitcond, label %for.end, label %for.body
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for.end:
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ret i32 %div
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}
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