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author | Arnold Schwaighofer <aschwaighofer@apple.com> | 2013-04-12 15:15:19 +0000 |
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committer | Arnold Schwaighofer <aschwaighofer@apple.com> | 2013-04-12 15:15:19 +0000 |
commit | 08a0e8f8dbae6314dade60e1ef92e73e89c5ff23 (patch) | |
tree | c92a7deba86db295ab34ac2acbcd84ed94d77325 /test/Transforms | |
parent | b6ad2bd51195f7675db0f71c5826a12a2b7090fc (diff) | |
download | external_llvm-08a0e8f8dbae6314dade60e1ef92e73e89c5ff23.zip external_llvm-08a0e8f8dbae6314dade60e1ef92e73e89c5ff23.tar.gz external_llvm-08a0e8f8dbae6314dade60e1ef92e73e89c5ff23.tar.bz2 |
LoopVectorizer: integer division is not a reduction operation
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
Diffstat (limited to 'test/Transforms')
-rw-r--r-- | test/Transforms/LoopVectorize/no_idiv_reduction.ll | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/test/Transforms/LoopVectorize/no_idiv_reduction.ll b/test/Transforms/LoopVectorize/no_idiv_reduction.ll new file mode 100644 index 0000000..cdfb3fd --- /dev/null +++ b/test/Transforms/LoopVectorize/no_idiv_reduction.ll @@ -0,0 +1,24 @@ +; RUN: opt -loop-vectorize -force-vector-width=2 -force-vector-unroll=1 -S < %s | FileCheck %s +@a = common global [128 x i32] zeroinitializer, align 16 + +;; Must not vectorize division reduction. Division is lossy. +define i32 @g() { +entry: + br label %for.body + +for.body: + ; CHECK: @g + ; CHECK-NOT: sdiv <2 x i32> + %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ] + %r.05 = phi i32 [ 80, %entry ], [ %div, %for.body ] + %arrayidx = getelementptr inbounds [128 x i32]* @a, i64 0, i64 %indvars.iv + %0 = load i32* %arrayidx, align 4 + %div = sdiv i32 %r.05, %0 + %indvars.iv.next = add i64 %indvars.iv, 1 + %lftr.wideiv = trunc i64 %indvars.iv.next to i32 + %exitcond = icmp eq i32 %lftr.wideiv, 1024 + br i1 %exitcond, label %for.end, label %for.body + +for.end: + ret i32 %div +} |