[Mesa-dev] [PATCH 2/3] i965/fs: Fix comparisions with uint negation.

[Eric Anholt]

The condmod instruction ends up generating garbage condition codes,
because apparently the comparison happens on the accumulator value (33
bits for UD), not the truncated value that would be written.

Fixes fs-op-neg-*
---
 src/mesa/drivers/dri/i965/brw_fs.cpp         |   13 +++++++++++++
 src/mesa/drivers/dri/i965/brw_fs.h           |    1 +
 src/mesa/drivers/dri/i965/brw_fs_emit.cpp    |   10 ++++++++++
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp |   25 +++++++++++++++++++++++++
 4 files changed, 49 insertions(+), 0 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 2000180..555d26d 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -1347,6 +1347,19 @@ fs_visitor::register_coalesce()
 	    interfered = true;
 	    break;
 	 }
+
+	 /* The accumulator result appears to get used for the
+	  * conditional modifier generation.  When negating a UD
+	  * value, there is a 33rd bit generated for the sign in the
+	  * accumulator value, so now you can't check, for example,
+	  * equality with a 32-bit value.  See piglit fs-op-neg-uint.
+	  */
+	 if (scan_inst->conditional_mod &&
+	     inst->src[0].negate &&
+	     inst->src[0].type == BRW_REGISTER_TYPE_UD) {
+	    interfered = true;
+	    break;
+	 }
       }
       if (interfered) {
 	 continue;
diff --git a/src/mesa/drivers/dri/i965/brw_fs.h b/src/mesa/drivers/dri/i965/brw_fs.h
index 56181a3..7a89413 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.h
+++ b/src/mesa/drivers/dri/i965/brw_fs.h
@@ -534,6 +534,7 @@ public:
 			       fs_inst *last_rhs_inst);
    void emit_assignment_writes(fs_reg &l, fs_reg &r,
 			       const glsl_type *type, bool predicated);
+   void resolve_ud_negate(fs_reg *reg);
 
    struct brw_reg interp_reg(int location, int channel);
    int setup_uniform_values(int loc, const glsl_type *type);
diff --git a/src/mesa/drivers/dri/i965/brw_fs_emit.cpp b/src/mesa/drivers/dri/i965/brw_fs_emit.cpp
index 4c158fe..7025347 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_emit.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_emit.cpp
@@ -636,6 +636,16 @@ fs_visitor::generate_code()
 
       for (unsigned int i = 0; i < 3; i++) {
 	 src[i] = brw_reg_from_fs_reg(&inst->src[i]);
+
+	 /* The accumulator result appears to get used for the
+	  * conditional modifier generation.  When negating a UD
+	  * value, there is a 33rd bit generated for the sign in the
+	  * accumulator value, so now you can't check, for example,
+	  * equality with a 32-bit value.  See piglit fs-op-neg-uvec4.
+	  */
+	 assert(!inst->conditional_mod ||
+		inst->src[i].type != BRW_REGISTER_TYPE_UD ||
+		!inst->src[i].negate);
       }
       dst = brw_reg_from_fs_reg(&inst->dst);
 
diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 07ea84f..24cc23c 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -317,6 +317,9 @@ fs_visitor::visit(ir_expression *ir)
       if (intel->gen < 5)
 	 temp.type = op[0].type;
 
+      resolve_ud_negate(&op[0]);
+      resolve_ud_negate(&op[1]);
+
       inst = emit(BRW_OPCODE_CMP, temp, op[0], op[1]);
       inst->conditional_mod = brw_conditional_for_comparison(ir->operation);
       emit(BRW_OPCODE_AND, this->result, this->result, fs_reg(0x1));
@@ -377,6 +380,8 @@ fs_visitor::visit(ir_expression *ir)
       if (intel->gen < 5)
 	 temp.type = op[0].type;
 
+      resolve_ud_negate(&op[0]);
+
       inst = emit(BRW_OPCODE_CMP, temp, op[0], fs_reg(0.0f));
       inst->conditional_mod = BRW_CONDITIONAL_NZ;
       inst = emit(BRW_OPCODE_AND, this->result, this->result, fs_reg(1));
@@ -401,6 +406,9 @@ fs_visitor::visit(ir_expression *ir)
       break;
 
    case ir_binop_min:
+      resolve_ud_negate(&op[0]);
+      resolve_ud_negate(&op[1]);
+
       if (intel->gen >= 6) {
 	 inst = emit(BRW_OPCODE_SEL, this->result, op[0], op[1]);
 	 inst->conditional_mod = BRW_CONDITIONAL_L;
@@ -416,6 +424,9 @@ fs_visitor::visit(ir_expression *ir)
       }
       break;
    case ir_binop_max:
+      resolve_ud_negate(&op[0]);
+      resolve_ud_negate(&op[1]);
+
       if (intel->gen >= 6) {
 	 inst = emit(BRW_OPCODE_SEL, this->result, op[0], op[1]);
 	 inst->conditional_mod = BRW_CONDITIONAL_GE;
@@ -1369,6 +1380,8 @@ fs_visitor::emit_bool_to_cond_code(ir_rvalue *ir)
 
 	 expr->operands[i]->accept(this);
 	 op[i] = this->result;
+
+	 resolve_ud_negate(&op[i]);
       }
 
       switch (expr->operation) {
@@ -1984,3 +1997,15 @@ fs_visitor::emit_fb_writes()
 
    this->current_annotation = NULL;
 }
+
+void
+fs_visitor::resolve_ud_negate(fs_reg *reg)
+{
+   if (reg->type != BRW_REGISTER_TYPE_UD ||
+       !reg->negate)
+      return;
+
+   fs_reg temp = fs_reg(this, glsl_type::uint_type);
+   emit(BRW_OPCODE_MOV, temp, *reg);
+   *reg = temp;
+}
-- 
1.7.6.3