From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg McGary To: Daniel Jacobowitz Cc: "J.T. Conklin" , gdb@sourceware.cygnus.com Subject: Re: SKIP_PROLOGUE() and prologue insn scheduling Date: Wed, 18 Jul 2001 09:31:00 -0000 Message-id: References: <5msnfv9nsp.fsf@orac.redback.com> <20010717163126.A5385@nevyn.them.org> X-SW-Source: 2001-07/msg00238.html Daniel Jacobowitz writes: > > The choice is whether SKIP_PROLOGUE() returns: > > 1) 1st user insn even though more prologue insns remain? > > 2) 1st user insn after final prologue insn? > [ ... ] > IMO, #1 is the way to go. It's regrettable in that a whole lot of > tests start failing, since we will display arguments wrong. But if the > prologue is being scheduled, it's possible to schedule part of the > prologue on the interior of a large if statement (which encompasses the > rest of the body of the function, say). If we do #2, we may never stop > in the function at all. That particular pathology should not occur. First, the RTL for prologue & epilogue is not generated until the flow2 pass, rather late in the game, and after such code motion could occur. Second, SKIP_PROLOGUE() must be written to stop scanning for prologue insns when it reaches the end of the first basic block, as demarcated by a jump or branch insn. Therefore, #2 remains a viable option as we would never place the breakpoint in conditionally-executed code. Greg