On 04/15/2013 11:22 PM, Martin Andersson wrote:
There is a hardware bug on Cayman where a BREAK/CONTINUE followed by
LOOP_STARTxxx for nested loops may put the branch stack into a state
such that ALU_PUSH_BEFORE doesn't work as expected. Workaround this
by replacing the ALU_PUSH_BEFORE with a PUSH + ALU
Fixes piglit tests EXT_transform_feedback/order*
v2: Use existing loop count and improve comment
---
src/gallium/drivers/r600/r600_shader.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)
diff --git a/src/gallium/drivers/r600/r600_shader.c
b/src/gallium/drivers/r600/r600_shader.c
index 6dbca50..f4398fd 100644
--- a/src/gallium/drivers/r600/r600_shader.c
+++ b/src/gallium/drivers/r600/r600_shader.c
@@ -5490,7 +5490,7 @@ static int tgsi_opdst(struct r600_shader_ctx *ctx)
return 0;
}
-static int emit_logic_pred(struct r600_shader_ctx *ctx, int opcode)
+static int emit_logic_pred(struct r600_shader_ctx *ctx, int opcode, int
alu_type)
{
struct r600_bytecode_alu alu;
int r;
@@ -5510,7 +5510,7 @@ static int emit_logic_pred(struct r600_shader_ctx *ctx,
int opcode)
alu.last = 1;
- r = r600_bytecode_add_alu_type(ctx->bc, &alu, CF_OP_ALU_PUSH_BEFORE);
+ r = r600_bytecode_add_alu_type(ctx->bc, &alu, alu_type);
if (r)
return r;
return 0;
@@ -5730,7 +5730,18 @@ static void break_loop_on_flag(struct r600_shader_ctx
*ctx, unsigned fc_sp)
static int tgsi_if(struct r600_shader_ctx *ctx)
{
- emit_logic_pred(ctx, ALU_OP2_PRED_SETNE_INT);
+ int alu_type = CF_OP_ALU_PUSH_BEFORE;
+
+ /* There is a hardware bug on Cayman where a BREAK/CONTINUE followed by
+ * LOOP_STARTxxx for nested loops may put the branch stack into a state
+ * such that ALU_PUSH_BEFORE doesn't work as expected. Workaround this
+ * by replacing the ALU_PUSH_BEFORE with a PUSH + ALU */
+ if (ctx->bc->chip_class == CAYMAN && ctx->bc->stack.loop > 1) {
+ r600_bytecode_add_cfinst(ctx->bc, CF_OP_PUSH);
Oh, it seems I overlooked potential issue here: jump address for PUSH is
not set properly, so I guess there will be GPU lockups in case of a
jump. Ideally we could set it to jump over the whole IF-ENDIF block if
there are no active threads, but I think it's a rare case, so simplest
fix is to avoid computation of the address and set jump address for PUSH
to the next instruction, like this:
ctx->bc->cf_last->cf_addr = ctx->bc->cf_last->id + 2;
We can improve it later but anyway ALU_PUSH_BEFORE never jumped at all
so I think at least we won't have any serious performance regressions.
Everything else looks ok, so I think I'll commit your patch with this
change soon if there are no objections.
Vadim
+ alu_type = CF_OP_ALU;
+ }
+
+ emit_logic_pred(ctx, ALU_OP2_PRED_SETNE_INT, alu_type);
r600_bytecode_add_cfinst(ctx->bc, CF_OP_JUMP);
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