Remove DCHECK from sort comparison function

Summary:
Our implementation of `std::sort()` (and other functions that take a
`Compare` object) does some sanity checks on the provided predicate, including
calling `comp(a, a)` and asserting that it's false. This was tripping a
`JIT_DCHECK()` in this comparison function. Remove it from the predicate and do
a separate pass to ensure uniqueness after sorting.

Reviewed By: alexmalyshev

Differential Revision: D56479803

fbshipit-source-id: e877d08d2f51271fd668fe1308e34aa571b1652b

cinderx/Jit/hir/hir.cpp

@@ -30,9 +30,19 @@ void DeoptBase::sortLiveRegs() {
       live_regs_.begin(),
       live_regs_.end(),
       [](const RegState& a, const RegState& b) {
-        JIT_DCHECK(a.reg != b.reg, "Same register should not be live twice");
         return a.reg->id() < b.reg->id();
       });
+
+  if (kPyDebug) {
+    // Check for uniqueness after sorting rather than inside the predicate
+    // passed to std::sort(), in case sort() performs extra comparisons to
+    // sanity-check our predicate.
+    auto it = std::adjacent_find(
+        live_regs_.begin(),
+        live_regs_.end(),
+        [](const RegState& a, const RegState& b) { return a.reg == b.reg; });
+    JIT_DCHECK(it == live_regs_.end(), "Register {} is live twice", *it->reg);
+  }
 }
 
 void Phi::setArgs(const std::unordered_map<BasicBlock*, Register*>& args) {