Limit LDS usage.

2019-11-22  Andrew Stubbs  <ams@codesourcery.com>

	gcc/
	* config/gcn/gcn.c (OMP_LDS_SIZE): Define.
	(ACC_LDS_SIZE): Define.
	(OTHER_LDS_SIZE): Define.
	(LDS_SIZE): Redefine using above.
	(gcn_expand_prologue): Initialize m0 with LDS_SIZE-1.

From-SVN: r278622

gcc/ChangeLog

+2019-11-22  Andrew Stubbs  <ams@codesourcery.com>
+
+	* config/gcn/gcn.c (OMP_LDS_SIZE): Define.
+	(ACC_LDS_SIZE): Define.
+	(OTHER_LDS_SIZE): Define.
+	(LDS_SIZE): Redefine using above.
+	(gcn_expand_prologue): Initialize m0 with LDS_SIZE-1.
+
 2019-11-22  Martin Sebor  <msebor@redhat.com>
 
 	PR tree-optimization/92501

gcc/config/gcn/gcn.c

@@ -70,10 +70,15 @@ int gcn_isa = 3;		/* Default to GCN3.  */
    worker-single mode to worker-partitioned mode), per workgroup.  Global
    analysis could calculate an exact bound, but we don't do that yet.
  
-   We reserve the whole LDS, which also prevents any other workgroup
-   sharing the Compute Unit.  */
+   We want to permit full occupancy, so size accordingly.  */
 
-#define LDS_SIZE 65536
+#define OMP_LDS_SIZE 0x600    /* 0x600 is 1/40 total, rounded down.  */
+#define ACC_LDS_SIZE 32768    /* Half of the total should be fine.  */
+#define OTHER_LDS_SIZE 65536  /* If in doubt, reserve all of it.  */
+
+#define LDS_SIZE (flag_openacc ? ACC_LDS_SIZE \
+		  : flag_openmp ? OMP_LDS_SIZE \
+		  : OTHER_LDS_SIZE)
 
 /* The number of registers usable by normal non-kernel functions.
    The SGPR count includes any special extra registers such as VCC.  */
@@ -2876,8 +2881,11 @@ gcn_expand_prologue ()
   /* Ensure that the scheduler doesn't do anything unexpected.  */
   emit_insn (gen_blockage ());
 
+  /* m0 is initialized for the usual LDS DS and FLAT memory case.
+     The low-part is the address of the topmost addressable byte, which is
+     size-1.  The high-part is an offset and should be zero.  */
   emit_move_insn (gen_rtx_REG (SImode, M0_REG),
-		  gen_int_mode (LDS_SIZE, SImode));
+		  gen_int_mode (LDS_SIZE-1, SImode));
 
   emit_insn (gen_prologue_use (gen_rtx_REG (SImode, M0_REG)));