Fix a nondeterminism in the ARM assembler.
Adding arbitrary records to ARM.td would break
basic-arm-instructions.s because selection of nop vs mov r0,r0 was
ambiguous (this will be tested by a subsequent addition to ARM.td).
An imperfect but sensible fix is to give precedence to match rules
that have more constraints.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162824 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/AsmMatcherEmitter.cpp b/utils/TableGen/AsmMatcherEmitter.cpp
index 097cbfc..9e8e946 100644
--- a/utils/TableGen/AsmMatcherEmitter.cpp
+++ b/utils/TableGen/AsmMatcherEmitter.cpp
@@ -488,6 +488,15 @@
return false;
}
+ // Give matches that require more features higher precedence. This is useful
+ // because we cannot define AssemblerPredicates with the negation of
+ // processor features. For example, ARM v6 "nop" may be either a HINT or
+ // MOV. With v6, we want to match HINT. The assembler has no way to
+ // predicate MOV under "NoV6", but HINT will always match first because it
+ // requires V6 while MOV does not.
+ if (RequiredFeatures.size() != RHS.RequiredFeatures.size())
+ return RequiredFeatures.size() > RHS.RequiredFeatures.size();
+
return false;
}