r600g: Workaround for a harware bug with nested loops on Cayman

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
v3: [Vadim Girlin] Set jump address for PUSH instructions

NOTE: This is a candidate for the 9.1 branch

Signed-off-by: Vadim Girlin <vadimgirlin@gmail.com>

diff --git a/src/gallium/drivers/r600/r600_shader.c b/src/gallium/drivers/r600/r600_shader.c
index 6dbca505cbe772528f6d998070a344c1422f1b41..f3e21874653e769664232f1b4941c8fccc8cca03 100644 (file)
--- 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 +5730,19 @@ 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);
+               ctx->bc->cf_last->cf_addr = ctx->bc->cf_last->id + 2;
+               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);