Ensure correct may_goto asm format

Check AsmOpPieces[1] to ensure may_goto asm format correct.

Author: Yonghong Song

llvm/lib/Target/BPF/BPFMIPeephole.cpp

@@ -710,7 +710,10 @@ bool BPFMIPreEmitPeephole::removeMayGotoZero() {
     // The asm insn must be a may_goto insn.
     SmallVector<StringRef, 4> AsmOpPieces;
     SplitString(AsmPieces[0], AsmOpPieces, " ");
-    if (AsmOpPieces[0] != "may_goto")
+    if (AsmOpPieces.size() != 2 || AsmOpPieces[0] != "may_goto")
+      continue;
+    // Enforce the format of 'may_goto <label>'.
+    if (AsmOpPieces[1] != "${0:l}" && AsmOpPieces[1] != "$0")
       continue;
 
     // Get the may_goto branch target.

llvm/test/CodeGen/BPF/may_goto.ll renamed to llvm/test/CodeGen/BPF/may_goto_1.ll

@@ -0,0 +1,27 @@
+; RUN: llc -mtriple=bpfel -mcpu=v3 -filetype=obj -o - %s | llvm-objdump --no-show-raw-insn -d - | FileCheck %s
+
+@j = dso_local local_unnamed_addr global i32 0, align 4
+
+define dso_local noundef i32 @foo() local_unnamed_addr {
+entry:
+  callbr void asm sideeffect "may_goto $0", "!i"()
+          to label %for.body [label %for.cond.cleanup]
+
+for.cond.cleanup:                                 ; preds = %for.body.2, %for.body.2, %for.body.1, %for.body, %entry
+  ret i32 0
+
+for.body:                                         ; preds = %entry
+  callbr void asm sideeffect "may_goto $0", "!i"()
+          to label %for.body.1 [label %for.cond.cleanup]
+
+for.body.1:                                       ; preds = %for.body
+  callbr void asm sideeffect "may_goto $0", "!i"()
+          to label %for.body.2 [label %for.cond.cleanup]
+
+for.body.2:                                       ; preds = %for.body.1
+  callbr void asm sideeffect "may_goto $0", "!i"()
+          to label %for.cond.cleanup [label %for.cond.cleanup]
+}
+
+; CHECK:       0:       w0 = 0x0
+; CHECK-NEXT:  1:       exit