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Re: [RS6000] Fix PR35907, vmx regs trashed
This implements register restore and frame pop via the frame pointer
if we happen to have one, which is slightly better than using the
backchain. I've also introduced ALWAYS_RESTORE_ALTIVEC_BEFORE_POP
and the changes necessary to do as the macro says. The idea here is
to make it easy to test whether it is worth having two copies of the
vmx register restore code in rs6000_emit_epilogue. I guess it isn't
that much of a maintenance burden, but we only gain one instruction
and then only when we have a large frame but don't use enough
registers to put the vmx area outside of valid stack below sp.
Bootstrapped and regression tested powerpc-linux and powerpc64-linux,
both ALWAYS_RESTORE_ALTIVEC_BEFORE_POP and
!ALWAYS_RESTORE_ALTIVEC_BEFORE_POP. OK for mainline?
* config/rs6000/rs6000.c (ALWAYS_RESTORE_ALTIVEC_BEFORE_POP): Define.
(rs6000_emit_epilogue): Use backchain to restore only when we
have a large frame. Make use of frame pointer to restore if we
have one. Handle ALWAYS_RESTORE_ALTIVEC_BEFORE_POP.
Index: gcc/config/rs6000/rs6000.c
===================================================================
--- gcc/config/rs6000/rs6000.c (revision 134387)
+++ gcc/config/rs6000/rs6000.c (working copy)
@@ -16228,6 +16228,10 @@ rs6000_output_function_prologue (FILE *f
rs6000_pic_labelno++;
}
+/* Non-zero if vmx regs are restored before the frame pop, zero if
+ we restore after the pop when possible. */
+#define ALWAYS_RESTORE_ALTIVEC_BEFORE_POP 0
+
/* Emit function epilogue as insns.
At present, dwarf2out_frame_debug_expr doesn't understand
@@ -16267,13 +16271,18 @@ rs6000_emit_epilogue (int sibcall)
|| current_function_calls_eh_return
|| info->first_fp_reg_save == 64
|| FP_SAVE_INLINE (info->first_fp_reg_save));
- use_backchain_to_restore_sp = (frame_pointer_needed
- || current_function_calls_alloca
- || info->total_size > 32767);
using_mtcr_multiple = (rs6000_cpu == PROCESSOR_PPC601
|| rs6000_cpu == PROCESSOR_PPC603
|| rs6000_cpu == PROCESSOR_PPC750
|| optimize_size);
+ /* Restore via the backchain when we have a large frame, since this
+ is more efficient than an addis, addi pair. The second condition
+ here will not trigger at the moment; We don't actually need a
+ frame pointer for alloca, but the generic parts of the compiler
+ give us one anyway. */
+ use_backchain_to_restore_sp = (info->total_size > 32767
+ || (current_function_calls_alloca
+ && !frame_pointer_needed));
if (WORLD_SAVE_P (info))
{
@@ -16374,8 +16383,9 @@ rs6000_emit_epilogue (int sibcall)
stack. */
if (TARGET_ALTIVEC_ABI
&& info->altivec_size != 0
- && DEFAULT_ABI != ABI_V4
- && info->altivec_save_offset < (TARGET_32BIT ? -220 : -288))
+ && (ALWAYS_RESTORE_ALTIVEC_BEFORE_POP
+ || (DEFAULT_ABI != ABI_V4
+ && info->altivec_save_offset < (TARGET_32BIT ? -220 : -288))))
{
int i;
@@ -16386,6 +16396,8 @@ rs6000_emit_epilogue (int sibcall)
gen_rtx_MEM (Pmode, sp_reg_rtx));
sp_offset = 0;
}
+ else if (frame_pointer_needed)
+ frame_reg_rtx = hard_frame_pointer_rtx;
for (i = info->first_altivec_reg_save; i <= LAST_ALTIVEC_REGNO; ++i)
if (info->vrsave_mask & ALTIVEC_REG_BIT (i))
@@ -16410,18 +16422,23 @@ rs6000_emit_epilogue (int sibcall)
if (TARGET_ALTIVEC
&& TARGET_ALTIVEC_VRSAVE
&& info->vrsave_mask != 0
- && DEFAULT_ABI != ABI_V4
- && info->vrsave_save_offset < (TARGET_32BIT ? -220 : -288))
+ && (ALWAYS_RESTORE_ALTIVEC_BEFORE_POP
+ || (DEFAULT_ABI != ABI_V4
+ && info->vrsave_save_offset < (TARGET_32BIT ? -220 : -288))))
{
rtx addr, mem, reg;
- if (use_backchain_to_restore_sp
- && frame_reg_rtx == sp_reg_rtx)
+ if (frame_reg_rtx == sp_reg_rtx)
{
- frame_reg_rtx = gen_rtx_REG (Pmode, 11);
- emit_move_insn (frame_reg_rtx,
- gen_rtx_MEM (Pmode, sp_reg_rtx));
- sp_offset = 0;
+ if (use_backchain_to_restore_sp)
+ {
+ frame_reg_rtx = gen_rtx_REG (Pmode, 11);
+ emit_move_insn (frame_reg_rtx,
+ gen_rtx_MEM (Pmode, sp_reg_rtx));
+ sp_offset = 0;
+ }
+ else if (frame_pointer_needed)
+ frame_reg_rtx = hard_frame_pointer_rtx;
}
addr = gen_rtx_PLUS (Pmode, frame_reg_rtx,
@@ -16433,17 +16450,11 @@ rs6000_emit_epilogue (int sibcall)
emit_insn (generate_set_vrsave (reg, info, 1));
}
- /* If we have a frame pointer, a call to alloca, or a large stack
- frame, restore the old stack pointer using the backchain. Otherwise,
- we know what size to update it with. */
+ /* If we have a large stack frame, restore the old stack pointer
+ using the backchain. */
if (use_backchain_to_restore_sp)
{
- if (frame_reg_rtx != sp_reg_rtx)
- {
- emit_move_insn (sp_reg_rtx, frame_reg_rtx);
- frame_reg_rtx = sp_reg_rtx;
- }
- else
+ if (frame_reg_rtx == sp_reg_rtx)
{
/* Under V.4, don't reset the stack pointer until after we're done
loading the saved registers. */
@@ -16454,6 +16465,30 @@ rs6000_emit_epilogue (int sibcall)
gen_rtx_MEM (Pmode, sp_reg_rtx));
sp_offset = 0;
}
+ else if (ALWAYS_RESTORE_ALTIVEC_BEFORE_POP
+ && DEFAULT_ABI == ABI_V4)
+ /* frame_reg_rtx has been set up by the altivec restore. */
+ ;
+ else
+ {
+ emit_move_insn (sp_reg_rtx, frame_reg_rtx);
+ frame_reg_rtx = sp_reg_rtx;
+ }
+ }
+ /* If we have a frame pointer, we can restore the old stack pointer
+ from it. */
+ else if (frame_pointer_needed)
+ {
+ frame_reg_rtx = sp_reg_rtx;
+ if (DEFAULT_ABI == ABI_V4)
+ frame_reg_rtx = gen_rtx_REG (Pmode, 11);
+
+ emit_insn (TARGET_32BIT
+ ? gen_addsi3 (frame_reg_rtx, hard_frame_pointer_rtx,
+ GEN_INT (info->total_size))
+ : gen_adddi3 (frame_reg_rtx, hard_frame_pointer_rtx,
+ GEN_INT (info->total_size)));
+ sp_offset = 0;
}
else if (info->push_p
&& DEFAULT_ABI != ABI_V4
@@ -16468,7 +16503,8 @@ rs6000_emit_epilogue (int sibcall)
}
/* Restore AltiVec registers if we have not done so already. */
- if (TARGET_ALTIVEC_ABI
+ if (!ALWAYS_RESTORE_ALTIVEC_BEFORE_POP
+ && TARGET_ALTIVEC_ABI
&& info->altivec_size != 0
&& (DEFAULT_ABI == ABI_V4
|| info->altivec_save_offset >= (TARGET_32BIT ? -220 : -288)))
@@ -16495,7 +16531,8 @@ rs6000_emit_epilogue (int sibcall)
}
/* Restore VRSAVE if we have not done so already. */
- if (TARGET_ALTIVEC
+ if (!ALWAYS_RESTORE_ALTIVEC_BEFORE_POP
+ && TARGET_ALTIVEC
&& TARGET_ALTIVEC_VRSAVE
&& info->vrsave_mask != 0
&& (DEFAULT_ABI == ABI_V4
--
Alan Modra
Australia Development Lab, IBM