On 11/29/08 14:45:49, Eric Botcazou wrote: > > Agreed. The routine that creates the errant REG_EQUAL note is > > lookup_as_function(). > > Really? Doesn't it only retrieve a pre-existing REG_EQUAL note?
It retrieves an equivalent rtx constant, if it exists. Before the patch, the constant that was returned is a word mode (DImode) constant with the value 0x100000000 (33 bits), which won't fit into an SImode value, and therefore isn't equivalent. The fix is to call gen_lowpart() in the case where the word mode constant is narrowed to a smaller mode. In the example, the lower 32 bits of the constant will be used, which is 0, and is the correct equivalent constant. cse_insn() calls lookup_as_function() ultimately through fold_rtx(), IIRC, and is the routine that writes the REG_EQUAL note.
