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Summary: Existing heuristic uses the ratio between the function entry frequency and the loop invocation frequency to find cold loops. However, even if the loop executes frequently, if it has a small trip count per each invocation, vectorization is not beneficial. On the other hand, even if the loop invocation frequency is much smaller than the function invocation frequency, if the trip count is high it is still beneficial to vectorize the loop. This patch uses estimated trip count computed from the profile metadata as a primary metric to determine coldness of the loop. If the estimated trip count cannot be computed, it falls back to the original heuristics. Reviewers: Ayal, mssimpso, mkuper, danielcdh, wmi, tejohnson Reviewed By: tejohnson Subscribers: tejohnson, mzolotukhin, llvm-commits Differential Revision: https://reviews.llvm.org/D32451 llvm-svn: 305729
92 lines
3.1 KiB
LLVM
92 lines
3.1 KiB
LLVM
; This test verifies that the loop vectorizer will not vectorizes low trip count
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; loops that require runtime checks (Trip count is computed with profile info).
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; REQUIRES: asserts
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; RUN: opt < %s -loop-vectorize -loop-vectorize-with-block-frequency -S | FileCheck %s
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target datalayout = "E-m:e-p:32:32-i64:32-f64:32:64-a:0:32-n32-S128"
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@tab = common global [32 x i8] zeroinitializer, align 1
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define i32 @foo_low_trip_count1(i32 %bound) {
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; Simple loop with low tripcount. Should not be vectorized.
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; CHECK-LABEL: @foo_low_trip_count1(
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; CHECK-NOT: <{{[0-9]+}} x i8>
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entry:
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br label %for.body
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for.body: ; preds = %for.body, %entry
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%i.08 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
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%arrayidx = getelementptr inbounds [32 x i8], [32 x i8]* @tab, i32 0, i32 %i.08
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%0 = load i8, i8* %arrayidx, align 1
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%cmp1 = icmp eq i8 %0, 0
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%. = select i1 %cmp1, i8 2, i8 1
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store i8 %., i8* %arrayidx, align 1
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%inc = add nsw i32 %i.08, 1
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%exitcond = icmp eq i32 %i.08, %bound
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br i1 %exitcond, label %for.end, label %for.body, !prof !1
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for.end: ; preds = %for.body
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ret i32 0
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}
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define i32 @foo_low_trip_count2(i32 %bound) !prof !0 {
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; The loop has a same invocation count with the function, but has a low
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; trip_count per invocation and not worth to vectorize.
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; CHECK-LABEL: @foo_low_trip_count2(
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; CHECK-NOT: <{{[0-9]+}} x i8>
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entry:
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br label %for.body
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for.body: ; preds = %for.body, %entry
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%i.08 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
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%arrayidx = getelementptr inbounds [32 x i8], [32 x i8]* @tab, i32 0, i32 %i.08
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%0 = load i8, i8* %arrayidx, align 1
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%cmp1 = icmp eq i8 %0, 0
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%. = select i1 %cmp1, i8 2, i8 1
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store i8 %., i8* %arrayidx, align 1
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%inc = add nsw i32 %i.08, 1
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%exitcond = icmp eq i32 %i.08, %bound
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br i1 %exitcond, label %for.end, label %for.body, !prof !1
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for.end: ; preds = %for.body
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ret i32 0
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}
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define i32 @foo_low_trip_count3(i1 %cond, i32 %bound) !prof !0 {
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; The loop has low invocation count compare to the function invocation count,
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; but has a high trip count per invocation. Vectorize it.
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; CHECK-LABEL: @foo_low_trip_count3(
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; CHECK: vector.body:
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entry:
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br i1 %cond, label %for.preheader, label %for.end, !prof !2
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for.preheader:
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br label %for.body
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for.body: ; preds = %for.body, %entry
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%i.08 = phi i32 [ 0, %for.preheader ], [ %inc, %for.body ]
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%arrayidx = getelementptr inbounds [32 x i8], [32 x i8]* @tab, i32 0, i32 %i.08
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%0 = load i8, i8* %arrayidx, align 1
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%cmp1 = icmp eq i8 %0, 0
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%. = select i1 %cmp1, i8 2, i8 1
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store i8 %., i8* %arrayidx, align 1
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%inc = add nsw i32 %i.08, 1
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%exitcond = icmp eq i32 %i.08, %bound
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br i1 %exitcond, label %for.end, label %for.body, !prof !3
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for.end: ; preds = %for.body
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ret i32 0
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}
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!0 = !{!"function_entry_count", i64 100}
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!1 = !{!"branch_weights", i32 100, i32 0}
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!2 = !{!"branch_weights", i32 10, i32 90}
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!3 = !{!"branch_weights", i32 10, i32 10000}
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