> -----Original Message----- > From: Ramana Radhakrishnan [mailto:ramana....@googlemail.com] > Sent: Wednesday, May 21, 2014 4:56 PM > To: Terry Guo > Cc: gcc-patches; Richard Earnshaw; Ramana Radhakrishnan > Subject: Re: [Patch, GCC/Thumb1] Improve 64bit constant load for Thumb1 > > -(define_split > +; Split the load of 64-bit constant into two loads for high and low > 32-bit parts respectively > +; to see if we can load them in fewer instructions or fewer cycles. > +; For the small 64-bit integer constants that satisfy constraint J, > the instruction pattern > +; thumb1_movdi_insn has a better way to handle them. > >+(define_split > >+ [(set (match_operand:ANY64 0 "arm_general_register_operand" "") > >+ (match_operand:ANY64 1 "const_double_operand" ""))] > >+ "TARGET_THUMB1 && reload_completed && !satisfies_constraint_J > (operands[1])" > >+ [(set (match_dup 0) (match_dup 1)) > >+ (set (match_dup 2) (match_dup 3))] > > Not ok - this splitter used to kick in in ARM state, now you've turned it off. > Look at the movdi patterns in ARM state which deal with it immediate > moves with a #. > > So, the condition should read > > (TARGET_32BIT) || ( TARGET_THUMB1 && ....) > > Ok with that change and if no regressions. > > regards > Ramana >
Thanks for reviewing. This is a total new splitter dedicated for Thumb1 targets. The one for ARM isn't touched. BR, Terry > > > > On Fri, Apr 11, 2014 at 8:36 AM, Terry Guo <terry....@arm.com> wrote: > > Hi there, > > > > Current gcc prefers to using two LDR instructions to load 64bit constants. > > This could miss some chances that 64bit load can be done in fewer > > instructions or fewer cycles. For example, below code to load > > 0x100000001 > > > > mov r0, #1 > > mov r1, #1 > > > > is better than current solution: > > > > ldr r1, .L2+4 > > ldr r0, .L2 > > .L2: > > .word 1 > > .word 1 > > > > The attached patch intends to split 64bit load to take advantage of > > such chances. Tested with gcc regression test on cortex-m0. No new > regressions. > > > > Is it ok to stage 1? > > > > BR, > > Terry > > > > gcc/ > > 2014-04-11 Terry Guo <terry....@arm.com> > > > > * config/arm/arm.md (split 64-bit constant for Thumb1): New > > split pattern. > > > > gcc/testsuite/ > > 2014-04-11 Terry Guo <terry....@arm.com> > > > > * gcc.target/arm/thumb1-load-64bit-constant-1.c: New test. > > * gcc.target/arm/thumb1-load-64bit-constant-2.c: Ditto. > > * gcc.target/arm/thumb1-load-64bit-constant-3.c: Ditto.
