ir3 compiler has an integer multiply-add instruction (MAD_S24)
that is used for different offset calculations in the backend.
Since we intend to move some of these calculations to NIR, we need
a new ALU op that can directly represent it.
---
src/compiler/nir/nir_opcodes.py | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/src/compiler/nir/nir_opcodes.py b/src/compiler/nir/nir_opcodes.py
index d32005846a6..abbb3627a33 100644
--- a/src/compiler/nir/nir_opcodes.py
+++ b/src/compiler/nir/nir_opcodes.py
@@ -892,3 +892,19 @@ dst.w = src3.x;
""")
+# Freedreno-specific opcode that maps directly to ir3_MAD_S24.
+# It is emitted by ir3_nir_lower_io_offsets pass when computing
+# byte-offsets for image store and atomics.
+#
+# The nir_algebraic expression below is: get 23 bits of the
+# two factors as unsigned and multiply them. If either of the
+# two was negative, invert sign of the product. Then add it src2.
+# @FIXME: I suspect there is a simpler expression for this.
+triop("imad24_ir3", tint, """
+unsigned f0 = ((unsigned) src0) & 0x7fffff;
+unsigned f1 = ((unsigned) src1) & 0x7fffff;
+dst = f0 * f1;
+if (src0 * src1 < 0)
+ dst = -dst;
+dst += src2;
+""")
--
2.20.1
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