On Tue, Jul 11, 2023 at 9:07 PM Roger Sayle <ro...@nextmovesoftware.com> wrote: > > > This patch fixes the regression PR target/110598 caused by my recent > addition of a peephole2. The intention of that optimization was to > simplify zeroing a register, followed by an IOR, XOR or PLUS operation > on it into a move, or as described in the comment: > ;; Peephole2 rega = 0; rega op= regb into rega = regb. > > The issue is that I'd failed to consider the (rare and unusual) case, > where regb is rega, where the transformation leads to the incorrect > "rega = rega", when it should be "rega = 0". The minimal fix is to > add a !reg_mentioned_p check to the recent peephole2. > > In addition to resolving the regression, I've added a second peephole2 > to optimize the problematic case above, which contains a false > dependency and is therefore tricky to optimize elsewhere. This is an > improvement over GCC 13, for example, that generates the redundant: > > xorl %edx, %edx > xorq %rdx, %rdx > > > 2023-07-11 Roger Sayle <ro...@nextmovesoftware.com> > > gcc/ChangeLog > PR target/110598 > * config/i386/i386.md (peephole2): Check !reg_mentioned_p when > optimizing rega = 0; rega op= regb for op in [XOR,IOR,PLUS]. > (peephole2): Simplify rega = 0; rega op= rega cases. > > gcc/testsuite/ChangeLog > PR target/110598 > * gcc.target/i386/pr110598.c: New test case.
OK. Thanks, Uros. > > > Thanks in advance (and apologies for any inconvenience), > Roger > -- >
