On 12/01/08 11:50:48, Eric Botcazou wrote: > > cse_insn() calls lookup_as_function() ultimately through fold_rtx(), IIRC, > > and is the routine that writes the REG_EQUAL note. > > OK, thanks. But I'm a little at a loss as to why this problem arises only > now: the problematic code in lookup_as_function is one decade old. Do you > happen to have older compilers around (say GCC 4.1.x based) that correctly > compile the testcase? If so, what happens differently with them?
Yeah, I was surprised as well. The compiler base line this problem arose on is 4.2.3, but I think that it will occur in both older and newer base lines. The problem is triggered by code generated by the UPC (Unified Parllel C) support that we've implemented in a project we call GCC/UPC. It fails on a small UPC test case, but a number of factors have to be present to trigger the problem. I tried developing a vanilla C test case to duplicate the problem, but have so far been unsuccessful. Internally, we use VIEW_CONVERT_EXPR to overlay a TImode container on top of a struct. There is no exact C equivalent, though a union comes close. I tried that, but couldn't replicate the exact set of events that have to be present to hit the problem. I send what I tried to you separately. Perhaps adding some sort of logging in lookup_as_function() that indicates narrowing is occurring, and then running all test cases (including Ada, because its unchecked_conversion is close to what we're doing internally) would turn something up?
