[amdgcn] Restrict registers available to non-kernel functions

Restrict the number of SGPRs and VGPRs available to non-kernel functions
to improve compute-unit occupancy with multiple threads.

2019-11-15  Kwok Cheung Yeung  <kcy@codesourcery.com>

	gcc/
	* config/gcn/gcn.c (default_requested_args): New.
	(gcn_parse_amdgpu_hsa_kernel_attribute): Initialize requested args
	set with default_requested_args.
	(gcn_conditional_register_usage): Limit register usage of non-kernel
	functions.  Reassign fixed registers if a non-standard set of args is
	requested.
	* config/gcn/gcn.h (FIXED_REGISTERS): Fix registers according to ABI.

From-SVN: r278301

3 files changed, 49 insertions, 30 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index fe8daf4..4de97a0 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,13 @@
+2019-11-15  Kwok Cheung Yeung  <kcy@codesourcery.com>
+
+	* config/gcn/gcn.c (default_requested_args): New.
+	(gcn_parse_amdgpu_hsa_kernel_attribute): Initialize requested args
+	set with default_requested_args.
+	(gcn_conditional_register_usage): Limit register usage of non-kernel
+	functions.  Reassign fixed registers if a non-standard set of args is
+	requested.
+	* config/gcn/gcn.h (FIXED_REGISTERS): Fix registers according to ABI.
+
 2019-11-15  Feng Xue  <fxue@os.amperecomputing.com>
 
 	PR ipa/92528
diff --git a/gcc/config/gcn/gcn.c b/gcc/config/gcn/gcn.c
index d2ec6e1..383e0aa 100644
--- a/gcc/config/gcn/gcn.c
+++ b/gcc/config/gcn/gcn.c
@@ -191,6 +191,17 @@ static const struct gcn_kernel_arg_type
   {"work_item_id_Z", NULL, V64SImode, FIRST_VGPR_REG + 2}
 };
 
+static const long default_requested_args
+	= (1 << PRIVATE_SEGMENT_BUFFER_ARG)
+	  | (1 << DISPATCH_PTR_ARG)
+	  | (1 << QUEUE_PTR_ARG)
+	  | (1 << KERNARG_SEGMENT_PTR_ARG)
+	  | (1 << PRIVATE_SEGMENT_WAVE_OFFSET_ARG)
+	  | (1 << WORKGROUP_ID_X_ARG)
+	  | (1 << WORK_ITEM_ID_X_ARG)
+	  | (1 << WORK_ITEM_ID_Y_ARG)
+	  | (1 << WORK_ITEM_ID_Z_ARG);
+
 /* Extract parameter settings from __attribute__((amdgpu_hsa_kernel ())).
    This function also sets the default values for some arguments.
  
@@ -201,10 +212,7 @@ gcn_parse_amdgpu_hsa_kernel_attribute (struct gcn_kernel_args *args,
 				       tree list)
 {
   bool err = false;
-  args->requested = ((1 << PRIVATE_SEGMENT_BUFFER_ARG)
-		     | (1 << QUEUE_PTR_ARG)
-		     | (1 << KERNARG_SEGMENT_PTR_ARG)
-		     | (1 << PRIVATE_SEGMENT_WAVE_OFFSET_ARG));
+  args->requested = default_requested_args;
   args->nargs = 0;
 
   for (int a = 0; a < GCN_KERNEL_ARG_TYPES; a++)
@@ -242,8 +250,6 @@ gcn_parse_amdgpu_hsa_kernel_attribute (struct gcn_kernel_args *args,
       args->requested |= (1 << a);
       args->order[args->nargs++] = a;
     }
-  args->requested |= (1 << WORKGROUP_ID_X_ARG);
-  args->requested |= (1 << WORK_ITEM_ID_Z_ARG);
 
   /* Requesting WORK_ITEM_ID_Z_ARG implies requesting WORK_ITEM_ID_X_ARG and
      WORK_ITEM_ID_Y_ARG.  Similarly, requesting WORK_ITEM_ID_Y_ARG implies
@@ -253,10 +259,6 @@ gcn_parse_amdgpu_hsa_kernel_attribute (struct gcn_kernel_args *args,
   if (args->requested & (1 << WORK_ITEM_ID_Y_ARG))
     args->requested |= (1 << WORK_ITEM_ID_X_ARG);
 
-  /* Always enable this so that kernargs is in a predictable place for
-     gomp_print, etc.  */
-  args->requested |= (1 << DISPATCH_PTR_ARG);
-
   int sgpr_regno = FIRST_SGPR_REG;
   args->nsgprs = 0;
   for (int a = 0; a < GCN_KERNEL_ARG_TYPES; a++)
@@ -2045,27 +2047,34 @@ gcn_secondary_reload (bool in_p, rtx x, reg_class_t rclass,
 static void
 gcn_conditional_register_usage (void)
 {
-  int i;
+  if (!cfun || !cfun->machine)
+    return;
 
-  /* FIXME: Do we need to reset fixed_regs?  */
+  if (cfun->machine->normal_function)
+    {
+      /* Restrict the set of SGPRs and VGPRs used by non-kernel functions.  */
+      for (int i = SGPR_REGNO (62); i <= LAST_SGPR_REG; i++)
+	fixed_regs[i] = 1, call_used_regs[i] = 1;
 
-/* Limit ourselves to 1/16 the register file for maximimum sized workgroups.
-   There are enough SGPRs not to limit those.
-   TODO: Adjust this more dynamically.  */
-  for (i = FIRST_VGPR_REG + 64; i <= LAST_VGPR_REG; i++)
-    fixed_regs[i] = 1, call_used_regs[i] = 1;
+      for (int i = VGPR_REGNO (24); i <= LAST_VGPR_REG; i++)
+	fixed_regs[i] = 1, call_used_regs[i] = 1;
 
-  if (!cfun || !cfun->machine || cfun->machine->normal_function)
-    {
-      /* Normal functions can't know what kernel argument registers are
-         live, so just fix the bottom 16 SGPRs, and bottom 3 VGPRs.  */
-      for (i = 0; i < 16; i++)
-	fixed_regs[FIRST_SGPR_REG + i] = 1;
-      for (i = 0; i < 3; i++)
-	fixed_regs[FIRST_VGPR_REG + i] = 1;
       return;
     }
 
+  /* If the set of requested args is the default set, nothing more needs to
+     be done.  */
+  if (cfun->machine->args.requested == default_requested_args)
+    return;
+
+  /* Requesting a set of args different from the default violates the ABI.  */
+  if (!leaf_function_p ())
+    warning (0, "A non-default set of initial values has been requested, "
+		"which violates the ABI!");
+
+  for (int i = SGPR_REGNO (0); i < SGPR_REGNO (14); i++)
+    fixed_regs[i] = 0;
+
   /* Fix the runtime argument register containing values that may be
      needed later.  DISPATCH_PTR_ARG and FLAT_SCRATCH_* should not be
      needed after the prologue so there's no need to fix them.  */
@@ -2073,10 +2082,10 @@ gcn_conditional_register_usage (void)
     fixed_regs[cfun->machine->args.reg[PRIVATE_SEGMENT_WAVE_OFFSET_ARG]] = 1;
   if (cfun->machine->args.reg[PRIVATE_SEGMENT_BUFFER_ARG] >= 0)
     {
+      /* The upper 32-bits of the 64-bit descriptor are not used, so allow
+	the containing registers to be used for other purposes.  */
       fixed_regs[cfun->machine->args.reg[PRIVATE_SEGMENT_BUFFER_ARG]] = 1;
       fixed_regs[cfun->machine->args.reg[PRIVATE_SEGMENT_BUFFER_ARG] + 1] = 1;
-      fixed_regs[cfun->machine->args.reg[PRIVATE_SEGMENT_BUFFER_ARG] + 2] = 1;
-      fixed_regs[cfun->machine->args.reg[PRIVATE_SEGMENT_BUFFER_ARG] + 3] = 1;
     }
   if (cfun->machine->args.reg[KERNARG_SEGMENT_PTR_ARG] >= 0)
     {
diff --git a/gcc/config/gcn/gcn.h b/gcc/config/gcn/gcn.h
index b3b2d1a..dd3789b 100644
--- a/gcc/config/gcn/gcn.h
+++ b/gcc/config/gcn/gcn.h
@@ -160,9 +160,9 @@
 
 #define FIXED_REGISTERS {			    \
     /* Scalars.  */				    \
-    0, 0, 0, 0, 0, 0, 0, 0, 0, 0,		    \
+    1, 1, 0, 0, 1, 1, 0, 0, 1, 1,		    \
 /*		fp    sp    lr.  */		    \
-    0, 0, 0, 0, 1, 1, 1, 1, 0, 0,		    \
+    1, 1, 0, 0, 1, 1, 1, 1, 0, 0,		    \
 /*  exec_save, cc_save */			    \
     1, 1, 1, 1, 0, 0, 0, 0, 0, 0,		    \
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0,		    \
@@ -180,7 +180,7 @@
     1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
     1, 1, 1, 1, 1, 1, 1, 1, 1, 1,		    \
     /* VGRPs */					    \
-    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
+    0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \