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6488deacf6
Summary: After their range checks were removed in 7f50c15be5c0, br_tables started being duplicated into their predecessors by tail folding. Unfortunately, when the br_tables were in loops this transformation introduced bad irreducible control flow which was later expanded into even more br_tables. This commit abuses the `isNotDuplicable` property to prevent this irreducible control flow from being introduced. This change saves a few dozen bytes of code size and has a negligible affect on performance for most of the large Emscripten benchmarks, but can improve performance significantly on microbenchmarks of switches in loops. Reviewers: aheejin, dschuff Subscribers: sbc100, jgravelle-google, hiraditya, sunfish, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D81628
70 lines
1.9 KiB
LLVM
70 lines
1.9 KiB
LLVM
; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers | FileCheck %s
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; This tests that indirectbr instructions are lowered to switches. Currently we
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; just re-use the IndirectBrExpand Pass; it has its own IR-level test.
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; So this test just ensures that the pass gets run and we can lower indirectbr
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target triple = "wasm32"
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@test1.targets = constant [4 x i8*] [i8* blockaddress(@test1, %bb0),
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i8* blockaddress(@test1, %bb1),
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i8* blockaddress(@test1, %bb2),
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i8* blockaddress(@test1, %bb3)]
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; Just check the barest skeleton of the structure
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; CHECK-LABEL: test1:
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; CHECK: i32.load
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; CHECK: i32.load
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; CHECK: loop
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; CHECK: block
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; CHECK: block
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; CHECK: block
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; CHECK: block
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; CHECK: br_table ${{[^,]+}}, 1, 2, 0
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; CHECK: end_block
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; CHECK: end_block
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; CHECK: end_block
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; CHECK: end_block
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; CHECK: br
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; CHECK: end_loop
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; CHECK: end_function
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; CHECK: test1.targets:
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; CHECK-NEXT: .int32
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; CHECK-NEXT: .int32
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; CHECK-NEXT: .int32
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; CHECK-NEXT: .int32
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define void @test1(i32* readonly %p, i32* %sink) #0 {
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entry:
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%i0 = load i32, i32* %p
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%target.i0 = getelementptr [4 x i8*], [4 x i8*]* @test1.targets, i32 0, i32 %i0
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%target0 = load i8*, i8** %target.i0
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; Only a subset of blocks are viable successors here.
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indirectbr i8* %target0, [label %bb0, label %bb1]
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bb0:
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store volatile i32 0, i32* %sink
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br label %latch
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bb1:
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store volatile i32 1, i32* %sink
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br label %latch
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bb2:
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store volatile i32 2, i32* %sink
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br label %latch
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bb3:
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store volatile i32 3, i32* %sink
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br label %latch
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latch:
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%i.next = load i32, i32* %p
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%target.i.next = getelementptr [4 x i8*], [4 x i8*]* @test1.targets, i32 0, i32 %i.next
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%target.next = load i8*, i8** %target.i.next
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; A different subset of blocks are viable successors here.
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indirectbr i8* %target.next, [label %bb1, label %bb2]
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}
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