[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, 51 insertions, 3 deletions

diff --git a/llvm/lib/Target/WebAssembly/InstPrinter/WebAssemblyInstPrinter.cpp b/llvm/lib/Target/WebAssembly/InstPrinter/WebAssemblyInstPrinter.cpp
index f92a9d0c661..60e52015242 100644
--- a/llvm/lib/Target/WebAssembly/InstPrinter/WebAssemblyInstPrinter.cpp
+++ b/llvm/lib/Target/WebAssembly/InstPrinter/WebAssemblyInstPrinter.cpp
@@ -16,6 +16,8 @@
 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
 #include "WebAssembly.h"
 #include "WebAssemblyMachineFunctionInfo.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCInstrInfo.h"
@@ -33,7 +35,7 @@ using namespace llvm;
 WebAssemblyInstPrinter::WebAssemblyInstPrinter(const MCAsmInfo &MAI,
                                                const MCInstrInfo &MII,
                                                const MCRegisterInfo &MRI)
-    : MCInstPrinter(MAI, MII, MRI) {}
+    : MCInstPrinter(MAI, MII, MRI), ControlFlowCounter(0) {}
 
 void WebAssemblyInstPrinter::printRegName(raw_ostream &OS,
                                           unsigned RegNo) const {
@@ -59,6 +61,52 @@ void WebAssemblyInstPrinter::printInst(const MCInst *MI, raw_ostream &OS,
 
   // Print any added annotation.
   printAnnotation(OS, Annot);
+
+  if (CommentStream) {
+    // Observe any effects on the control flow stack, for use in annotating
+    // control flow label references.
+    switch (MI->getOpcode()) {
+    default:
+      break;
+    case WebAssembly::LOOP: {
+      // Grab the TopLabel value first so that labels print in numeric order.
+      uint64_t TopLabel = ControlFlowCounter++;
+      ControlFlowStack.push_back(std::make_pair(ControlFlowCounter++, false));
+      printAnnotation(OS, "label" + utostr(TopLabel) + ':');
+      ControlFlowStack.push_back(std::make_pair(TopLabel, true));
+      break;
+    }
+    case WebAssembly::BLOCK:
+      ControlFlowStack.push_back(std::make_pair(ControlFlowCounter++, false));
+      break;
+    case WebAssembly::END_LOOP:
+      ControlFlowStack.pop_back();
+      printAnnotation(
+          OS, "label" + utostr(ControlFlowStack.pop_back_val().first) + ':');
+      break;
+    case WebAssembly::END_BLOCK:
+      printAnnotation(
+          OS, "label" + utostr(ControlFlowStack.pop_back_val().first) + ':');
+      break;
+    }
+
+    // Annotate any control flow label references.
+    unsigned NumFixedOperands = Desc.NumOperands;
+    SmallSet<uint64_t, 8> Printed;
+    for (unsigned i = 0, e = MI->getNumOperands(); i < e; ++i) {
+      const MCOperandInfo &Info = Desc.OpInfo[i];
+      if (!(i < NumFixedOperands
+                ? (Info.OperandType == WebAssembly::OPERAND_BASIC_BLOCK)
+                : (Desc.TSFlags & WebAssemblyII::VariableOpImmediateIsLabel)))
+        continue;
+      uint64_t Depth = MI->getOperand(i).getImm();
+      if (!Printed.insert(Depth).second)
+        continue;
+      const auto &Pair = ControlFlowStack.rbegin()[Depth];
+      printAnnotation(OS, utostr(Depth) + ": " + (Pair.second ? "up" : "down") +
+                              " to label" + utostr(Pair.first));
+    }
+  }
 }
 
 static std::string toString(const APFloat &FP) {
@@ -100,7 +148,7 @@ void WebAssemblyInstPrinter::printOperand(const MCInst *MI, unsigned OpNo,
   } else if (Op.isImm()) {
     assert((OpNo < MII.get(MI->getOpcode()).getNumOperands() ||
             (MII.get(MI->getOpcode()).TSFlags &
-                     WebAssemblyII::VariableOpIsImmediate)) &&
+             WebAssemblyII::VariableOpIsImmediate)) &&
            "WebAssemblyII::VariableOpIsImmediate should be set for "
            "variable_ops immediate ops");
     if (MII.get(MI->getOpcode()).TSFlags &
@@ -117,7 +165,7 @@ void WebAssemblyInstPrinter::printOperand(const MCInst *MI, unsigned OpNo,
   } else {
     assert((OpNo < MII.get(MI->getOpcode()).getNumOperands() ||
             (MII.get(MI->getOpcode()).TSFlags &
-                     WebAssemblyII::VariableOpIsImmediate)) &&
+             WebAssemblyII::VariableOpIsImmediate)) &&
            "WebAssemblyII::VariableOpIsImmediate should be set for "
            "variable_ops expr ops");
     assert(Op.isExpr() && "unknown operand kind in printOperand");