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[WebAssembly] Emit br_table for most switch instructions 

Summary:
Always convert switches to br_tables unless there is only one case,
which is equivalent to a simple branch. This reduces code size for wasm,
and we defer possible jump table optimizations to the VM.
Addresses PR41502.

Reviewers: kripken, sunfish

Subscribers: dschuff, sbc100, jgravelle-google, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60966

llvm-svn: 359038
This commit is contained in:
Heejin Ahn 2019-04-23 21:30:30 +00:00
parent a746f2b73c
commit b9f282d384
2 changed files with 36 additions and 42 deletions
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5
llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
View File

@ -270,6 +270,11 @@ WebAssemblyTargetLowering::WebAssemblyTargetLowering(
MaxStoresPerMemset = 1;
MaxStoresPerMemsetOptSize = 1;
}
// Always convert switches to br_tables unless there is only one case, which
// is equivalent to a simple branch. This reduces code size for wasm, and we
// defer possible jump table optimizations to the VM.
setMinimumJumpTableEntries(2);
}
TargetLowering::AtomicExpansionKind

73
llvm/test/CodeGen/WebAssembly/cfg-stackify.ll
View File

@ -384,19 +384,13 @@ if.end:
; CHECK-NEXT: .functype test4 (i32) -> (){{$}}
; CHECK: block {{$}}
; CHECK-NEXT: block {{$}}
; CHECK: br_if 0, $pop{{[0-9]+}}{{$}}
; CHECK: br_if 1, $pop{{[0-9]+}}{{$}}
; CHECK: br 1{{$}}
; CHECK: br_if 0, $pop{{[0-9]+}}{{$}}
; CHECK: br 1{{$}}
; CHECK-NEXT: .LBB{{[0-9]+}}_2:
; CHECK-NEXT: end_block{{$}}
; CHECK-NEXT: br_table $0, 0, 0, 0, 0, 0, 0{{$}}
; CHECK-NEXT: .LBB{{[0-9]+}}_3:
; CHECK-NEXT: end_block{{$}}
; CHECK-NEXT: block {{$}}
; CHECK: br_if 0, $pop{{[0-9]+}}{{$}}
; CHECK: br_if 1, $pop{{[0-9]+}}{{$}}
; CHECK-NEXT: .LBB{{[0-9]+}}_5:
; CHECK-NEXT: end_block{{$}}
; CHECK-NEXT: return{{$}}
; CHECK-NEXT: .LBB{{[0-9]+}}_6:
; CHECK-NEXT: end_block{{$}}
; CHECK-NEXT: return{{$}}
define void @test4(i32 %t) {
entry:
@ -646,29 +640,30 @@ end:
; CHECK-LABEL: test10:
; CHECK: .LBB{{[0-9]+}}_1:
; CHECK-NEXT: loop {{$}}
; CHECK-NOT: block
; CHECK: br_if 0, {{[^,]+}}{{$}}
; CHECK: br_if 0, {{[^,]+}}{{$}}
; CHECK: .LBB{{[0-9]+}}_3:
; CHECK-NEXT: block {{$}}
; CHECK-NEXT: loop {{$}}
; CHECK-NOT: block
; CHECK: .LBB{{[0-9]+}}_4:
; CHECK-NEXT: loop {{$}}
; CHECK-NOT: block
; CHECK: br_if 0, {{[^,]+}}{{$}}
; CHECK: br_if 0, {{[^,]+}}{{$}}
; CHECK-NEXT: end_loop{{$}}
; CHECK: br_if 1, {{[^,]+}}{{$}}
; CHECK-NOT: block
; CHECK: br_if 0, {{[^,]+}}{{$}}
; CHECK-NEXT: block {{$}}
; CHECK: br_if 0, {{[^,]+}}{{$}}
; CHECK: br 3{{$}}
; CHECK-NEXT: .LBB{{[0-9]+}}_7:
; CHECK-NEXT: end_block{{$}}
; CHECK: block {{$}}
; CHECK-NEXT: br_table $0, 0, 3, 1, 2, 0
; CHECK-NEXT: .LBB{{[0-9]+}}_8:
; CHECK-NEXT: end_block{{$}}
; CHECK-NEXT: end_loop{{$}}
; CHECK-NOT: block
; CHECK: br_if 1, {{[^,]+}}{{$}}
; CHECK-NEXT: return{{$}}
; CHECK-NEXT: .LBB{{[0-9]+}}_9:
; CHECK-NEXT: end_block{{$}}
; CHECK-NOT: block
; CHECK: br 0{{$}}
; CHECK: br 0{{$}}
; CHECK-NEXT: .LBB{{[0-9]+}}_10:
; CHECK-NEXT: end_loop{{$}}
define void @test10() {
bb0:
br label %bb1
@ -772,31 +767,25 @@ bb8:
; CHECK-LABEL: test12:
; CHECK: .LBB{{[0-9]+}}_1:
; CHECK-NEXT: block {{$}}
; CHECK-NEXT: loop {{$}}
; CHECK-NOT: block
; CHECK: block {{$}}
; CHECK-NEXT: block {{$}}
; CHECK: br_if 0, {{[^,]+}}{{$}}
; CHECK-NOT: block
; CHECK: br_if 1, {{[^,]+}}{{$}}
; CHECK-NOT: block
; CHECK: br_if 1, {{[^,]+}}{{$}}
; CHECK-NEXT: br 3{{$}}
; CHECK-NEXT: block {{$}}
; CHECK-NEXT: block {{$}}
; CHECK: br_if 0, {{[^,]+}}{{$}}
; CHECK: br_if 2, {{[^,]+}}{{$}}
; CHECK: br_if 1, {{[^,]+}}{{$}}
; CHECK-NEXT: br 2{{$}}
; CHECK-NEXT: .LBB{{[0-9]+}}_4:
; CHECK-NEXT: end_block{{$}}
; CHECK-NOT: block
; CHECK: br_if 0, {{[^,]+}}{{$}}
; CHECK-NOT: block
; CHECK: br_if 2, {{[^,]+}}{{$}}
; CHECK-NEXT: .LBB{{[0-9]+}}_6:
; CHECK-NEXT: end_block{{$}}
; CHECK-NOT: block
; CHECK: br 0{{$}}
; CHECK-NEXT: .LBB{{[0-9]+}}_7:
; CHECK-NEXT: end_loop{{$}}
; CHECK-NEXT: br_table $2, 1, 0, 0, 0, 1, 1{{$}}
; CHECK-NEXT: .LBB{{[0-9]+}}_5:
; CHECK-NEXT: end_block{{$}}
; CHECK-NEXT: return{{$}}
; CHECK-NEXT: .LBB{{[0-9]+}}_6:
; CHECK-NEXT: end_block{{$}}
; CHECK: br 0{{$}}
; CHECK-NEXT: .LBB{{[0-9]+}}_7:
; CHECK-NEXT: end_loop{{$}}
define void @test12(i8* %arg) {
bb:
br label %bb1