[wasm] Fix -Wsign-compare warnings.

src/wasm/ast-decoder.cc

Index: src/wasm/ast-decoder.cc
diff --git a/src/wasm/ast-decoder.cc b/src/wasm/ast-decoder.cc
index a2d0a3f0dea04fc42bdb79dda0fadcd0588ca982..af436f96debe25d259232cebee592174549cd3ff 100644
--- a/src/wasm/ast-decoder.cc
+++ b/src/wasm/ast-decoder.cc
@@ -800,7 +800,8 @@ class WasmFullDecoder : public WasmDecoder {
               if (c->false_env != nullptr) {
                 // End the true branch of a one-armed if.
                 Goto(c->false_env, c->end_env);
-                if (ssa_env_->go() && stack_.size() != c->stack_depth) {
+                if (ssa_env_->go() &&
+                    static_cast<int>(stack_.size()) != c->stack_depth) {
                   error("end of if expected empty stack");
                   stack_.resize(c->stack_depth);
                 }
@@ -1435,7 +1436,7 @@ class WasmFullDecoder : public WasmDecoder {
       // Unreachable code is essentially not typechecked.
       return {pc_, nullptr, kAstEnd};
     }
-    if (stack_depth == stack_.size()) {
+    if (stack_depth == static_cast<int>(stack_.size())) {
       Value val = {pc_, nullptr, kAstStmt};
       return val;
     } else {
@@ -1460,8 +1461,7 @@ class WasmFullDecoder : public WasmDecoder {
       Goto(ssa_env_, c->end_env);
     } else {
       // Merge the value(s) into the end of the block.
-      if (static_cast<size_t>(c->stack_depth + c->merge.arity) >
-          stack_.size()) {
+      if (c->stack_depth + c->merge.arity > stack_.size()) {
         error(
             pc_, pc_,
             "expected at least %d values on the stack for br to @%d, found %d",
@@ -1477,7 +1477,7 @@ class WasmFullDecoder : public WasmDecoder {
     if (!ssa_env_->go()) return;
     // Merge the value(s) into the end of the block.
     int arity = static_cast<int>(c->merge.arity);
-    if (c->stack_depth + arity != stack_.size()) {
+    if (c->stack_depth + arity != static_cast<int>(stack_.size())) {
       error(pc_, pc_, "expected %d elements on the stack for fallthru to @%d",
             arity, startrel(c->pc));
       return;
@@ -1493,7 +1493,7 @@ class WasmFullDecoder : public WasmDecoder {
     if (!ssa_env_->go()) return;
     // Fallthru must match arity exactly.
     int arity = static_cast<int>(c->merge.arity);
-    if (c->stack_depth + arity != stack_.size()) {
+    if (c->stack_depth + arity != static_cast<int>(stack_.size())) {
       error(pc_, pc_, "expected %d elements on the stack for fallthru to @%d",
             arity, startrel(c->pc));
       return;