Fix unused label filter for CUDA PTX output (#3717)

- Previously this filter did not correctly identify used labels in
  CUDA PTX output, which caused it to remove important labels.

lib/parsers/asm-parser.js

@@ -116,6 +116,7 @@ export class AsmParser extends AsmRegex {
         const startBlock = /\.cfi_startproc/;
         const endBlock = /\.cfi_endproc/;
         let inFunction = false;
+        let inNvccCode = false;
 
         // Scan through looking for definite label usages (ones used by opcodes),
         // and ones that are weakly used: that is, their use is conditional on another label.
@@ -138,6 +139,8 @@ export class AsmParser extends AsmRegex {
                 inFunction = true;
             } else if (endBlock.test(line)) {
                 inFunction = false;
+            } else if (this.cudaBeginDef.test(line)) {
+                inNvccCode = true;
             }
 
             if (inCustomAssembly > 0) line = this.fixLabelIndentation(line);
@@ -163,14 +166,14 @@ export class AsmParser extends AsmRegex {
             match = line.match(labelFind);
             if (!match) continue;
 
-            if (!filterDirectives || this.hasOpcode(line, false) || definesFunction) {
+            if (!filterDirectives || this.hasOpcode(line, inNvccCode) || definesFunction) {
                 // Only count a label as used if it's used by an opcode, or else we're not filtering directives.
                 for (const label of match) labelsUsed[label] = true;
             } else {
                 // If we have a current label, then any subsequent opcode or data definition's labels are referred to
                 // weakly by that label.
                 const isDataDefinition = !!this.dataDefn.test(line);
-                const isOpcode = this.hasOpcode(line, false);
+                const isOpcode = this.hasOpcode(line, inNvccCode);
                 if (isDataDefinition || isOpcode) {
                     for (const currentLabel of currentLabelSet) {
                         if (inFunction && isDataDefinition) {