[Mesa-dev] [PATCH 14/21] i965: Disallow saturation for MACH operations

[Ben Widawsky]

"As mach is used to generate part of the 64-bit DWord integer results,
saturation modifier should not be used. In fact, saturation modifier should not
be used for any of these four instructions."

I believe this never actually occurred anyway, and no tests should be effected.

Similar to previous patches, this actually applies to the whole MUL/MACH macro
operation, but it's easier to just catch it at MACH, since that is the only
thing we use MACH for.

Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 src/mesa/drivers/dri/i965/brw_fs_saturate_propagation.cpp | 2 +-
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp              | 2 +-
 src/mesa/drivers/dri/i965/brw_shader.cpp                  | 8 ++++++--
 src/mesa/drivers/dri/i965/brw_shader.h                    | 2 +-
 4 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_saturate_propagation.cpp b/src/mesa/drivers/dri/i965/brw_fs_saturate_propagation.cpp
index a9966a4..840b86f 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_saturate_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_saturate_propagation.cpp
@@ -72,7 +72,7 @@ opt_saturate_propagation_local(fs_visitor *v, bblock_t *block)
                inst->saturate = false;
                progress = true;
             } else if (src_end_ip <= ip || inst->dst.equals(inst->src[0])) {
-               if (scan_inst->can_do_saturate()) {
+               if (scan_inst->can_do_saturate(v->brw)) {
                   scan_inst->saturate = true;
                   inst->saturate = false;
                   progress = true;
diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 98f1b0d..96ed17e 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -350,7 +350,7 @@ fs_visitor::try_emit_saturate(ir_expression *ir)
     */
    fs_inst *modify = get_instruction_generating_reg(pre_inst, last_inst, src);
    if (modify && modify->regs_written == modify->dst.width / 8 &&
-       modify->can_do_saturate()) {
+       modify->can_do_saturate(this->brw)) {
       modify->saturate = true;
       this->result = src;
       return true;
diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp b/src/mesa/drivers/dri/i965/brw_shader.cpp
index 3891f43..006efe3 100644
--- a/src/mesa/drivers/dri/i965/brw_shader.cpp
+++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
@@ -702,7 +702,7 @@ backend_instruction::can_do_source_mods() const
 }
 
 bool
-backend_instruction::can_do_saturate() const
+backend_instruction::can_do_saturate(const struct brw_context *brw) const
 {
    switch (opcode) {
    case BRW_OPCODE_ADD:
@@ -717,7 +717,6 @@ backend_instruction::can_do_saturate() const
    case BRW_OPCODE_LINE:
    case BRW_OPCODE_LRP:
    case BRW_OPCODE_MAC:
-   case BRW_OPCODE_MACH:
    case BRW_OPCODE_MAD:
    case BRW_OPCODE_MATH:
    case BRW_OPCODE_MOV:
@@ -740,6 +739,11 @@ backend_instruction::can_do_saturate() const
    case SHADER_OPCODE_SIN:
    case SHADER_OPCODE_SQRT:
       return true;
+   case BRW_OPCODE_MACH:
+      if (brw->gen < 8)
+         return true;
+      else
+         return false;
    default:
       return false;
    }
diff --git a/src/mesa/drivers/dri/i965/brw_shader.h b/src/mesa/drivers/dri/i965/brw_shader.h
index 05434a7..4c4bb1a 100644
--- a/src/mesa/drivers/dri/i965/brw_shader.h
+++ b/src/mesa/drivers/dri/i965/brw_shader.h
@@ -86,7 +86,7 @@ struct backend_instruction : public exec_node {
    bool is_math() const;
    bool is_control_flow() const;
    bool can_do_source_mods() const;
-   bool can_do_saturate() const;
+   bool can_do_saturate(const struct brw_context *brw) const;
    bool reads_accumulator_implicitly() const;
    bool writes_accumulator_implicitly(struct brw_context *brw) const;
 
-- 
2.2.1