[llvm] AMDGPU: Move asm constraint physreg parsing to utils (PR #150903)

[Matt Arsenault via llvm-commits]

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@@ -1541,6 +1541,42 @@ bool shouldEmitConstantsToTextSection(const Triple &TT) {
   return TT.getArch() == Triple::r600;
 }
 
+static bool isValidRegPrefix(char C) {
+  return C == 'v' || C == 's' || C == 'a';
+}
+
+std::tuple<char, unsigned, unsigned>
+parseAsmConstraintPhysReg(StringRef Constraint) {
+  StringRef RegName = Constraint;
+  if (!RegName.consume_front("{") || !RegName.consume_back("}"))
+    return {};
+
+  char Kind = RegName.front();
+  if (!isValidRegPrefix(Kind))
+    return {};
+
+  RegName = RegName.drop_front();
+  if (RegName.consume_front("[")) {
+    unsigned Idx, End;
+    bool Failed = RegName.consumeInteger(10, Idx);
+    Failed |= !RegName.consume_front(":");
+    Failed |= RegName.consumeInteger(10, End);
+    Failed |= !RegName.consume_back("]");
+    if (!Failed) {
+      unsigned NumRegs = End - Idx + 1;
+      if (NumRegs > 1)
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arsenm wrote:

Doesn't appear to be an issue, the cases that would hit overflow fail the parse 

https://github.com/llvm/llvm-project/pull/150903