[Mesa-dev] [PATCH 1/2] nir: Handle <bits>=32 case in bitfield_insert lowering.

[Matt Turner]

The OpenGL specifications for bitfieldInsert() says:

   The result will be undefined if <offset> or <bits> is negative, or if
   the sum of <offset> and <bits> is greater than the number of bits
   used to store the operand.

Therefore passing bits=32, offset=0 is legal and defined in GLSL.

But the earlier SM5 bfi opcode is specified to accept a bitfield width
ranging from 0-31. As such, Intel and AMD instructions read only the low
5 bits of the width operand, making them not able to implement the
GLSL-specified behavior directly.

This commit fixes the lowering of bitfield_insert to handle the trivial
case of <bits> = 32 as

   bitfieldInsert:
      bits > 31 ? insert : bfi(bfm(bits, offset), insert, base)

Fixes:
   ES31-CTS.shader_bitfield_operation.bitfieldInsert.uint_2
   ES31-CTS.shader_bitfield_operation.bitfieldInsert.uvec4_3
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92595
---
These two patches replace 8/9 and 9/9 of the previous series.
The first 7 patches from it have been reviewed and committed.

 src/glsl/nir/nir_opcodes.py       | 1 +
 src/glsl/nir/nir_opt_algebraic.py | 6 +++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/glsl/nir/nir_opcodes.py b/src/glsl/nir/nir_opcodes.py
index 1c65def..3e43438 100644
--- a/src/glsl/nir/nir_opcodes.py
+++ b/src/glsl/nir/nir_opcodes.py
@@ -558,6 +558,7 @@ triop("fcsel", tfloat, "(src0 != 0.0f) ? src1 : src2")
 opcode("bcsel", 0, tuint, [0, 0, 0],
       [tbool, tuint, tuint], "", "src0 ? src1 : src2")
 
+# SM5 bfi assembly
 triop("bfi", tuint, """
 unsigned mask = src0, insert = src1, base = src2;
 if (mask == 0) {
diff --git a/src/glsl/nir/nir_opt_algebraic.py b/src/glsl/nir/nir_opt_algebraic.py
index 1eb044a..0d31e39 100644
--- a/src/glsl/nir/nir_opt_algebraic.py
+++ b/src/glsl/nir/nir_opt_algebraic.py
@@ -225,9 +225,13 @@ optimizations = [
 
    # Misc. lowering
    (('fmod', a, b), ('fsub', a, ('fmul', b, ('ffloor', ('fdiv', a, b)))), 'options->lower_fmod'),
-   (('bitfield_insert', a, b, c, d), ('bfi', ('bfm', d, c), b, a), 'options->lower_bitfield_insert'),
    (('uadd_carry', a, b), ('b2i', ('ult', ('iadd', a, b), a)), 'options->lower_uadd_carry'),
    (('usub_borrow', a, b), ('b2i', ('ult', a, b)), 'options->lower_usub_borrow'),
+
+   (('bitfield_insert', 'base', 'insert', 'offset', 'bits'),
+    ('bcsel', ('ilt', 31, 'bits'), 'insert',
+              ('bfi', ('bfm', 'bits', 'offset'), 'insert', 'base')),
+    'options->lower_bitfield_insert'),
 ]
 
 # Add optimizations to handle the case where the result of a ternary is
-- 
2.4.9