From 818f5ac5fc6eabef6dfaa3753ea3e5f811a9037f Mon Sep 17 00:00:00 2001 From: Andrew Trick Date: Wed, 29 Aug 2012 03:52:57 +0000 Subject: [PATCH] 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. llvm-svn: 162824 --- llvm/utils/TableGen/AsmMatcherEmitter.cpp | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/llvm/utils/TableGen/AsmMatcherEmitter.cpp b/llvm/utils/TableGen/AsmMatcherEmitter.cpp index 097cbfc68087..9e8e9462cc65 100644 --- a/llvm/utils/TableGen/AsmMatcherEmitter.cpp +++ b/llvm/utils/TableGen/AsmMatcherEmitter.cpp @@ -488,6 +488,15 @@ struct MatchableInfo { 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; }