[WebAssembly] Make CFG stackification independent of basic-block labels.

This patch changes the way labels are referenced. Instead of referencing the
basic-block label name (eg. .LBB0_0), instructions now just have an immediate
which indicates the depth in the control-flow stack to find a label to jump to.
This makes them much closer to what we expect to have in the binary encoding,
and avoids the problem of basic-block label names not being explicit in the
binary encoding.

Also, it terminates blocks and loops with end_block and end_loop instructions,
rather than basic-block label names, for similar reasons.

This will also fix problems where two constructs appear to have the same label,
because we no longer explicitly use labels, so consumers that need labels will
presumably create their own labels, and presumably they won't reuse labels
when they do.

This patch does make the code a little more awkward to read; as a partial
mitigation, this patch also introduces comments showing where the labels are,
and comments on each branch showing where it's branching to.

llvm-svn: 257505

1 files changed, 8 insertions, 8 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td b/llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td
index 1c06b08597a..d2852012be1 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td
@@ -42,32 +42,32 @@ let Defs = [ARGUMENTS] in {
 // jump tables, so in practice we don't ever use TABLESWITCH_I64 in wasm32 mode
 // currently.
 // Set TSFlags{0} to 1 to indicate that the variable_ops are immediates.
+// Set TSFlags{2} to 1 to indicate that the immediates represent labels.
 let isTerminator = 1, hasCtrlDep = 1, isBarrier = 1 in {
 def TABLESWITCH_I32 : I<(outs), (ins I32:$index, bb_op:$default, variable_ops),
                         [(WebAssemblytableswitch I32:$index, bb:$default)],
                         "tableswitch\t$index, $default"> {
   let TSFlags{0} = 1;
+  let TSFlags{2} = 1;
 }
 def TABLESWITCH_I64 : I<(outs), (ins I64:$index, bb_op:$default, variable_ops),
                         [(WebAssemblytableswitch I64:$index, bb:$default)],
                         "tableswitch\t$index, $default"> {
   let TSFlags{0} = 1;
+  let TSFlags{2} = 1;
 }
 } // isTerminator = 1, hasCtrlDep = 1, isBarrier = 1
 
-// Placemarkers to indicate the start of a block or loop scope. These
+// Placemarkers to indicate the start or end of a block or loop scope. These
 // use/clobber EXPR_STACK to prevent them from being moved into the middle of
 // an expression tree.
 let Uses = [EXPR_STACK], Defs = [EXPR_STACK] in {
-def BLOCK     : I<(outs), (ins bb_op:$dst), [], "block   \t$dst">;
-def LOOP      : I<(outs), (ins bb_op:$dst), [], "loop    \t$dst">;
+def BLOCK     : I<(outs), (ins), [], "block">;
+def LOOP      : I<(outs), (ins), [], "loop">;
+def END_BLOCK : I<(outs), (ins), [], "end_block">;
+def END_LOOP  : I<(outs), (ins), [], "end_loop">;
 } // Uses = [EXPR_STACK], Defs = [EXPR_STACK]
 
-// 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">;