[llvm-commits] [llvm] r162824 - /llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp

[Andrew Trick]

Author: atrick
Date: Tue Aug 28 22:52:57 2012
New Revision: 162824

URL: http://llvm.org/viewvc/llvm-project?rev=162824&view=rev
Log:
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.

Modified:
    llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp

Modified: llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp?rev=162824&r1=162823&r2=162824&view=diff
==============================================================================
--- llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp (original)
+++ llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp Tue Aug 28 22:52:57 2012
@@ -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;
   }