bdc0afc871
There are some workloads that are negatively impacted by using jump tables when the number of entries is small. The SPEC2017 perlbench benchmark is one example of this, where increasing the threshold to around 13 gives a ~1.5% improvement on neoverse-v1. I chose the minimum threshold based on empirical evidence rather than science, and just manually increased the threshold until I got the best performance without impacting other workloads. For neoverse-v1 I saw around ~0.2% improvement in the SPEC2017 integer geomean, and no overall change for neoverse-n1. If we find issues with this threshold later on we can always revisit this. The most significant SPEC2017 score changes on neoverse-v1 were: 500.perlbench_r: +1.6% 520.omnetpp_r: +0.6% and the rest saw changes < 0.5%. I updated CodeGen/AArch64/min-jump-table.ll to reflect the new threshold. For most of the affected tests I manually set the min number of entries back to 4 on the RUN line because the tests seem to rely upon this behaviour.
76 lines
1.7 KiB
LLVM
76 lines
1.7 KiB
LLVM
; RUN: llc -o - %s -mtriple=aarch64-none-linux-gnu -mattr=+force-32bit-jump-tables -aarch64-min-jump-table-entries=4 -aarch64-enable-atomic-cfg-tidy=0 | FileCheck %s
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; RUN: llc -o - %s -mtriple=aarch64-none-linux-gnu -mcpu=exynos-m3 -aarch64-min-jump-table-entries=4 -aarch64-enable-atomic-cfg-tidy=0 | FileCheck %s
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; Exynos doesn't want jump tables to be compressed for now.
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define i32 @test_jumptable(i32 %in) {
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switch i32 %in, label %def [
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i32 0, label %lbl1
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i32 1, label %lbl2
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i32 2, label %lbl3
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i32 4, label %lbl4
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]
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; CHECK-LABEL: test_jumptable:
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; CHECK: adrp [[JTPAGE:x[0-9]+]], .LJTI0_0
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; CHECK: add x[[JT:[0-9]+]], [[JTPAGE]], {{#?}}:lo12:.LJTI0_0
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; CHECK: [[PCREL_LBL:.Ltmp.*]]:
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; CHECK-NEXT: adr [[PCBASE:x[0-9]+]], [[PCREL_LBL]]
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; CHECK: ldrsw x[[OFFSET:[0-9]+]], [x[[JT]], {{x[0-9]+}}, lsl #2]
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; CHECK: add [[DEST:x[0-9]+]], [[PCBASE]], x[[OFFSET]]
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; CHECK: br [[DEST]]
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; CHECK: .LJTI0_0:
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; CHECK-NEXT: .word .LBB{{.*}}-[[PCREL_LBL]]
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def:
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ret i32 0
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lbl1:
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ret i32 1
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lbl2:
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ret i32 2
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lbl3:
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ret i32 4
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lbl4:
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ret i32 8
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}
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define i32 @test_jumptable_minsize(i32 %in) minsize {
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switch i32 %in, label %def [
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i32 0, label %lbl1
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i32 1, label %lbl2
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i32 2, label %lbl3
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i32 4, label %lbl4
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]
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; CHECK-LABEL: test_jumptable_minsize:
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; CHECK: adrp [[JTPAGE:x[0-9]+]], .LJTI1_0
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; CHECK: add x[[JT:[0-9]+]], [[JTPAGE]], {{#?}}:lo12:.LJTI1_0
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; CHECK: adr [[PCBASE:x[0-9]+]], [[JTBASE:.LBB[0-9]+_[0-9]+]]
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; CHECK: ldrb w[[OFFSET:[0-9]+]], [x[[JT]], {{x[0-9]+}}]
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; CHECK: add [[DEST:x[0-9]+]], [[PCBASE]], x[[OFFSET]], lsl #2
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; CHECK: br [[DEST]]
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def:
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ret i32 0
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lbl1:
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ret i32 1
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lbl2:
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ret i32 2
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lbl3:
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ret i32 4
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lbl4:
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ret i32 8
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}
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