Three-source instructions have a vertical stride overloaded to 4, which
prevents directly using vec4 uniforms as arguments. Instead we need to
insert a MOV instruction to do the replication for the three-source
instruction.
With this in place, we can use three-source instructions in the vertex
shader. While some thought needs to go into deciding whether its better
to use a three-source instruction rather than a sequence of equivalent
instructions (when one or more sources are uniforms or immediates), this
will allow us to skip a lot of ugly lowering code and use the BFE and
BFI2 instructions directly.
---
These patches should go before my ARB_gpu_shader5 series, and allow me to
drop
[PATCH 07/16] glsl: Add bitfieldInsert-to-bfm/bitops lowering pass.
[PATCH 08/16] glsl: Add BFE-to-bitops lowering pass.
src/mesa/drivers/dri/i965/brw_vec4.h | 2 ++
src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp | 23 +++++++++++++++++++++++
2 files changed, 25 insertions(+)
diff --git a/src/mesa/drivers/dri/i965/brw_vec4.h
b/src/mesa/drivers/dri/i965/brw_vec4.h
index 697ab86..c280922 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4.h
+++ b/src/mesa/drivers/dri/i965/brw_vec4.h
@@ -430,6 +430,8 @@ public:
void emit_scs(ir_instruction *ir, enum prog_opcode op,
dst_reg dst, const src_reg &src);
+ src_reg fix_3src_operand(src_reg src);
+
void emit_math1_gen6(enum opcode opcode, dst_reg dst, src_reg src);
void emit_math1_gen4(enum opcode opcode, dst_reg dst, src_reg src);
void emit_math(enum opcode opcode, dst_reg dst, src_reg src);
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
index 2fb8482..69e805d 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
@@ -224,6 +224,29 @@ vec4_visitor::emit_dp(dst_reg dst, src_reg src0, src_reg
src1, unsigned elements
}
src_reg
+vec4_visitor::fix_3src_operand(src_reg src)
+{
+ /* Using vec4 uniforms in SIMD4x2 programs is difficult. You'd like to be
+ * able to use vertical stride of zero to replicate the vec4 uniform, like
+ *
+ * g3<0;4,1>:f - [0, 4][1, 5][2, 6][3, 7]
+ *
+ * But you can't, since vertical stride is always four in three-source
+ * instructions. Instead, insert a MOV instruction to do the replication so
+ * that the three-source instruction can consume it.
+ */
+
+ /* The MOV is only needed if the source is a uniform or immediate. */
+ if (src.file != UNIFORM && src.file != IMM)
+ return src;
+
+ dst_reg expanded = dst_reg(this, glsl_type::vec4_type);
+ expanded.type = src.type;
+ emit(MOV(expanded, src));
+ return src_reg(expanded);
+}
+
+src_reg
vec4_visitor::fix_math_operand(src_reg src)
{
/* The gen6 math instruction ignores the source modifiers --
--
1.8.1.5
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