[TableGen][AsmWriterEmitter] Use a deterministic order to sort InstrAliases

Inside an alias group, when ordering instruction aliases, we rely
on the priority field to sort them.
When the priority is not set or more generally when there is a tie between
two aliases, we used to rely on the lexicographic order. However, this
order can change for the anonymous records when more instruction, intrinsic,
etc. are inserted.

For instance, given two anonymous records r1 and r2 with respective name
A_999 and A_1000, their lexicography order will be r2 then r1. Now, if
an instruction is added before them, their name will become respectively
A_1000 and A_1001, thus the lexicography order will be r1 then r2, i.e.,
it changed.

If that happens in an alias group, the assembly output would prefer a
different alias for no apparent good reasons.

A way to fix that is to use proper priority for all aliases, but we
can also make the tie breaker comparison smarter and use a deterministic
ordering. This is what this patch does.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294695 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/utils/TableGen/AsmWriterEmitter.cpp b/utils/TableGen/AsmWriterEmitter.cpp
index a7c6104aaa214500a2867b8441246bf339e43e9b..61ebece99e92ec05e78e23800c5207466bc8bcd7 100644 (file)
--- a/utils/TableGen/AsmWriterEmitter.cpp
+++ b/utils/TableGen/AsmWriterEmitter.cpp
@@ -741,7 +741,7 @@ struct AliasPriorityComparator {
     if (LHS.second ==  RHS.second) {
       // We don't actually care about the order, but for consistency it
       // shouldn't depend on pointer comparisons.
-      return LHS.first.TheDef->getName() < RHS.first.TheDef->getName();
+      return LessRecordByID()(LHS.first.TheDef, RHS.first.TheDef);
     }
 
     // Aliases with larger priorities should be considered first.