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[WebAssembly] Always print loop end labels

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WebAssembly is currently using labels to end scopes, so for example a
loop scope looks like this:

BB0_0:
  loop BB0_1
  ...
BB0_1:

with BB0_0 being the label of the first block not in the loop. This
requires that the label be printed even when it's only reachable via
fallthrough. To arrange this, insert a no-op LOOP_END instruction in
such cases at the end of the loop.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@253901 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2015-11-23 19:12:37 +00:00
parent 236067a61b
commit 5aafb6def5
4 changed files with 23 additions and 1 deletions
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4
lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
View File

@ -221,6 +221,10 @@ void WebAssemblyAsmPrinter::EmitInstruction(const MachineInstr *MI) {
// These represent values which are live into the function entry, so there's
// no instruction to emit.
break;
case WebAssembly::LOOP_END:
// This is a no-op which just exists to tell AsmPrinter.cpp that there's a
// fallthrough which nevertheless requires a label for the destination here.
break;
default: {
WebAssemblyMCInstLower MCInstLowering(OutContext, *this);
MCInst TmpInst;

12
lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
View File

@ -289,11 +289,21 @@ static void PlaceMarkers(MachineFunction &MF, const MachineLoopInfo &MLI,
MachineBasicBlock *Bottom = Loop->getBottomBlock();
auto Iter = next(MachineFunction::iterator(Bottom));
if (Iter == MF.end()) {
MF.push_back(MF.CreateMachineBasicBlock());
MachineBasicBlock *Label = MF.CreateMachineBasicBlock();
// Give it a fake predecessor so that AsmPrinter prints its label.
Label->addSuccessor(Label);
MF.push_back(Label);
Iter = next(MachineFunction::iterator(Bottom));
}
BuildMI(MBB, MBB.begin(), DebugLoc(), TII.get(WebAssembly::LOOP))
.addMBB(&*Iter);
// Emit a special no-op telling the asm printer that we need a label
// to close the loop scope, even though the destination is only
// reachable by fallthrough.
if (!Bottom->back().isBarrier())
BuildMI(*Bottom, Bottom->end(), DebugLoc(),
TII.get(WebAssembly::LOOP_END));
}
// Place the BLOCK for MBB if MBB is branched to from above.

5
lib/Target/WebAssembly/WebAssemblyInstrControl.td
View File

@ -39,6 +39,11 @@ def TABLESWITCH_I64 : I<(outs), (ins I64:$index, variable_ops),
def BLOCK : I<(outs), (ins bb_op:$dst), [], "block \t$dst">;
def LOOP : I<(outs), (ins bb_op:$dst), [], "loop \t$dst">;
// No-op to indicate to the AsmPrinter that a loop ends here, so a
// basic block label is needed even if it wouldn't otherwise appear so.
let isTerminator = 1, hasCtrlDep = 1 in
def LOOP_END : I<(outs), (ins), []>;
multiclass RETURN<WebAssemblyRegClass vt> {
def RETURN_#vt : I<(outs), (ins vt:$val), [(WebAssemblyreturn vt:$val)],
"return \t$val">;

3
test/CodeGen/WebAssembly/cfg-stackify.ll
View File

@ -186,6 +186,7 @@ entry:
; CHECK: BB7_1:
; CHECK: i32.store $0, $pop{{[0-9]+}}{{$}}
; CHECK: br BB7_1{{$}}
; CHECK: BB7_2:
define i32 @minimal_loop(i32* %p) {
entry:
store volatile i32 0, i32* %p
@ -200,6 +201,7 @@ loop:
; CHECK: BB8_1:
; CHECK: loop BB8_2{{$}}
; CHECK: br_if $pop{{[0-9]+}}, BB8_1{{$}}
; CHECK: BB8_2:
; CHECK: return ${{[0-9]+}}{{$}}
define i32 @simple_loop(i32* %p, i32 %a) {
entry:
@ -285,6 +287,7 @@ exit:
; CHECK: BB11_5:
; CHECK: BB11_6:
; CHECK: br BB11_1{{$}}
; CHECK: BB11_7:
define i32 @doublediamond_in_a_loop(i32 %a, i32 %b, i32* %p) {
entry:
br label %header