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Switch lowering: order bit tests by branch weight.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235912 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hans Wennborg 2015-04-27 20:21:17 +00:00
parent d455682f39
commit 84145dcd08
2 changed files with 50 additions and 1 deletions
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5
lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
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@ -7482,12 +7482,15 @@ bool SelectionDAGBuilder::buildBitTests(CaseClusterVector &Clusters,
CB->Bits++;
}
CB->ExtraWeight += Clusters[i].Weight;
assert(CB->ExtraWeight >= Clusters[i].Weight && "Weight sum overflowed!");
TotalWeight += Clusters[i].Weight;
}
BitTestInfo BTI;
std::sort(CBV.begin(), CBV.end(), [](const CaseBits &a, const CaseBits &b) {
// FIXME: Sort by weight.
// Sort by weight first, number of bits second.
if (a.ExtraWeight != b.ExtraWeight)
return a.ExtraWeight > b.ExtraWeight;
return a.Bits > b.Bits;
});

46
test/CodeGen/X86/switch.ll
View File

@ -367,3 +367,49 @@ return: ret void
; CHECK-LABEL: int_max_table_cluster
; CHECK: jmpq *.LJTI
}
define void @bt_order_by_weight(i32 %x) {
entry:
switch i32 %x, label %return [
i32 0, label %bb0
i32 3, label %bb0
i32 6, label %bb0
i32 1, label %bb1
i32 4, label %bb1
i32 7, label %bb1
i32 2, label %bb2
i32 5, label %bb2
i32 8, label %bb2
i32 9, label %bb2
], !prof !1
bb0: tail call void @g(i32 0) br label %return
bb1: tail call void @g(i32 1) br label %return
bb2: tail call void @g(i32 2) br label %return
return: ret void
; Cases 1,4,7 have a very large branch weight (which shouldn't overflow), so
; their bit test should come first. 0,3,6 and 2,5,8,9 both have a weight of 12,
; but the latter set has more cases, so should be tested for earlier.
; CHECK-LABEL: bt_order_by_weight
; 146 = 2^1 + 2^4 + 2^7
; CHECK: movl $146
; CHECK: btl
; 292 = 2^2 + 2^5 + 2^8 + 2^9
; CHECK: movl $804
; CHECK: btl
; 73 = 2^0 + 2^3 + 2^6
; CHECK: movl $73
; CHECK: btl
}
!1 = !{!"branch_weights",
; Default:
i32 1,
; Cases 0,3,6:
i32 4, i32 4, i32 4,
; Cases 1,4,7:
i32 4294967295, i32 2, i32 4294967295,
; Cases 2,5,8,9:
i32 3, i32 3, i32 3, i32 3}