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Fix a SimplifyCFG typo that leads to unbounded optimization #35604

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Jan 27, 2021
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Fix a SimplifyCFG typo that leads to unbounded optimization #35604

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2 changes: 1 addition & 1 deletion lib/SILOptimizer/Transforms/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1393,7 +1393,7 @@ bool SimplifyCFG::simplifyBranchBlock(BranchInst *BI) {
// Eliminating the trampoline can expose opportunities to improve the
// new block we branch to.
if (LoopHeaders.count(DestBB))
LoopHeaders.insert(BB);
LoopHeaders.insert(trampolineDest.destBB);

addToWorklist(trampolineDest.destBB);
BI->eraseFromParent();
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66 changes: 66 additions & 0 deletions test/SILOptimizer/simplify_cfg_simple.sil
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Expand Up @@ -7,6 +7,11 @@ sil_stage canonical
import Builtin
import Swift

internal enum Enum {
case one
case two
}

// CHECK-LABEL: sil @simple_test : $@convention(thin) () -> () {
// CHECK: bb0:
// CHECK-NEXT: tuple
Expand All @@ -27,3 +32,64 @@ bb3:
%9999 = tuple ()
return %9999 : $()
}

// Test that SimplifyCFG::simplifyBlocks, tryJumpThreading does not
// perform unbounded loop peeling.
//
// rdar://73357726 ([SR-14068]: Compiling with optimisation runs indefinitely for grpc-swift)
// CHECK-LABEL: sil @testInfinitePeeling : $@convention(method) (Builtin.Int64, Enum) -> () {
//
// There is only one switch_enum blocks, and it is no longer in a loop.
// CHECK: bb0(%0 : $Builtin.Int64, %1 : $Enum):
// CHECK: switch_enum %1 : $Enum, case #Enum.one!enumelt: bb3, case #Enum.two!enumelt: bb4
// CHECK: bb1:
// CHECK: br bb8
// CHECK: bb2:
// CHECK: br bb5(%{{.*}} : $Enum)
//
// This is the original cond_br block
// CHECK: bb3:
// CHECK: cond_br %{{.*}}, bb2, bb1
// CHECK: bb4:
// CHECK: br bb5(%1 : $Enum)
//
// This is the cond_br block after jump-threading.
// CHECK: bb5(%{{.*}} : $Enum):
// CHECK: cond_br %{{.*}}, bb6, bb7
// CHECK: bb6:
// CHECK: br bb5(%{{.*}} : $Enum)
// CHECK: bb7:
// CHECK: br bb8
// CHECK: bb8:
// CHECK: return %19 : $()
// CHECK-LABEL: } // end sil function 'testInfinitePeeling'
sil @testInfinitePeeling : $@convention(method) (Builtin.Int64, Enum) -> () {
bb0(%0 : $Builtin.Int64, %1 : $Enum):
%2 = integer_literal $Builtin.Int64, 99999999
br bb1(%0 : $Builtin.Int64, %1 : $Enum)

bb1(%4 : $Builtin.Int64, %5 : $Enum):
switch_enum %5 : $Enum, case #Enum.one!enumelt: bb4, default bb5

bb2(%7 : $Builtin.Int64, %8 : $Enum):
%9 = builtin "cmp_slt_Int64"(%2 : $Builtin.Int64, %7 : $Builtin.Int64) : $Builtin.Int1
cond_br %9, bb3, bb6

bb3:
br bb1(%7 : $Builtin.Int64, %8 : $Enum)

bb4:
%12 = integer_literal $Builtin.Int64, 1
%13 = integer_literal $Builtin.Int1, -1
%14 = builtin "sadd_with_overflow_Int64"(%4 : $Builtin.Int64, %12 : $Builtin.Int64, %13 : $Builtin.Int1) : $(Builtin.Int64, Builtin.Int1)
%15 = tuple_extract %14 : $(Builtin.Int64, Builtin.Int1), 0
%16 = enum $Enum, #Enum.two!enumelt
br bb2(%15 : $Builtin.Int64, %16 : $Enum)

bb5:
br bb2(%2 : $Builtin.Int64, %5 : $Enum)

bb6:
%19 = tuple ()
return %19 : $()
}