On Sun, Dec 6, 2015 at 11:50 PM, Patrick Palka <patr...@parcs.ath.cx> wrote: > There is a minor inconsistency in the folding behavior within the C > frontend. The C frontend does not currently fold the expression "x", > where x is a const int, yet the FE does fold the expression "x + 0". > > This happens because decl_constant_value is called in c_fully_fold only > while recursing over the operands of the expression being folded, i.e. > there is no top-level call to decl_constant_value to handle the case > where the expression being folded happens to be a singular expression > such as "x", as opposed to "x + 5" (where x is a const variable). > > To fix this inconsistency, this patch calls decl_constant_value in > c_fully fold after folding the given expression. > > Bootstrap + regtest in progress on x86_64-pc-linux-gnu, OK to commit if > testing succeeds?
It just occurred to me that this change is not completely safe because calling c_fully_fold on an lvalue can now return an rvalue. Callers of c_fully_fold are not prepared to handle this. Indeed, this patch causes a couple of regressions in the handling asm() memory operands due to this implicit lvalue-rvalue conversion.