f3731d34fa
Unrolling a loop with compile-time unknown trip count results in a remainder loop. The remainder loop executes the remaining iterations of the original loop when the original trip count is not a multiple of the unroll factor. For better profile counts maintenance throughout the optimization pipeline, I'm assigning an artificial weight to the latch branch of the remainder loop. A remainder loop runs up to as many times as the unroll factor subtracted by 1. Therefore I'm assigning the maximum possible trip count as the back edge weight. This should be more accurate than the default non-profile weight, which assumes the back edge runs much more frequently than the exit edge. Differential Revision: https://reviews.llvm.org/D83187
35 lines
1.4 KiB
LLVM
35 lines
1.4 KiB
LLVM
; RUN: opt < %s -S -loop-unroll -unroll-runtime=true -unroll-count=4 | FileCheck %s
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; RUN: opt < %s -S -passes=loop-unroll -unroll-runtime=true -unroll-count=4 | FileCheck %s
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;; Check that the remainder loop is properly assigned a branch weight for its latch branch.
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; CHECK-LABEL: @test(
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; CHECK-LABEL: for.body:
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; CHECK: br i1 [[COND1:%.*]], label %for.end.loopexit.unr-lcssa.loopexit, label %for.body, !prof ![[#PROF:]], !llvm.loop ![[#LOOP:]]
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; CHECK-LABEL: for.body.epil:
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; CHECK: br i1 [[COND2:%.*]], label %for.body.epil, label %for.end.loopexit.epilog-lcssa, !prof ![[#PROF2:]], !llvm.loop ![[#LOOP2:]]
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; CHECK: ![[#PROF]] = !{!"branch_weights", i32 1, i32 9999}
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; CHECK: ![[#PROF2]] = !{!"branch_weights", i32 3, i32 1}
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define i3 @test(i3* %a, i3 %n) {
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entry:
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%cmp1 = icmp eq i3 %n, 0
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br i1 %cmp1, label %for.end, label %for.body
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for.body:
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%indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %entry ]
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%sum.02 = phi i3 [ %add, %for.body ], [ 0, %entry ]
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%arrayidx = getelementptr inbounds i3, i3* %a, i64 %indvars.iv
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%0 = load i3, i3* %arrayidx
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%add = add nsw i3 %0, %sum.02
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%indvars.iv.next = add i64 %indvars.iv, 1
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%lftr.wideiv = trunc i64 %indvars.iv.next to i3
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%exitcond = icmp eq i3 %lftr.wideiv, %n
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br i1 %exitcond, label %for.end, label %for.body, !prof !0
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for.end:
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%sum.0.lcssa = phi i3 [ 0, %entry ], [ %add, %for.body ]
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ret i3 %sum.0.lcssa
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}
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!0 = !{!"branch_weights", i32 1, i32 9999}
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