Re: [PATCH v2 1/2] gas, aarch64: Add AdvSIMD lut extension

["Richard Earnshaw (lists)" <Richard.Earnshaw@arm.com>]

On 16/05/2024 11:35, Saurabh Jha wrote:
> Introduces instructions for the Advanced SIMD lut extension for AArch64. They are documented in the following links:
> * luti2: https://developer.arm.com/documentation/ddi0602/2024-03/SIMD-FP-Instructions/LUTI2--Lookup-table-read-with-2-bit-indices-?lang=en
> * luti4: https://developer.arm.com/documentation/ddi0602/2024-03/SIMD-FP-Instructions/LUTI4--Lookup-table-read-with-4-bit-indices-?lang=en
> 
> These instructions needed definition of some new operands. We will first
> discuss operands for the third operand of the instructions and then
> discuss a vector register list operand needed for the second operand.
> 
> The third operands are vectors with bit indices and without type
> qualifiers. They are called Em_INDEX1_14, Em_INDEX2_13, and Em_INDEX3_12
> and they have 1 bit, 2 bit, and 3 bit indices respectively. For these
> new operands, we defined new parsing case branch and a new instruction
> class. We also modified the existing reglane inserters and extractors
> to handle the new operands. The lsb and width of these operands are
> the same as many existing operands but the convention is to give
> different names to fields that serve different purpose so we
> introduced new fields in aarch64-opc.c and aarch64-opc.h for these
> operands.
> 
> For the second operand of these instructions, we introduced a new
> operand called LVn_LUT. This represents a vector register list with
> stride 1. We defined new inserter and extractor for this new operand and
> it is encoded in FLD_Rn. We are enforcing the number of registers in the
> reglist using opcode flag rather than operand flag as this is what other
> SIMD vector register list operands are doing. The disassembly also uses
> opcode flag to print the correct number of registers.
> ---
> Hi,
> 
> Regression tested for aarch64-none-elf and found no regressions.
> 
> Ok for binutils-master? I don't have commit access so can someone please commit on my behalf?
> 
> Regards,
> Saurabh

A couple of minor nits:

+++ b/gas/testsuite/gas/aarch64/advsimd-lut-illegal.s
@@ -0,0 +1,128 @@
+// Operand mismatch
+luti2	v2.16b, { v4.8h }, v8[1]
+luti2	v2.8h, { v4.16b }, v8[1]
...

In assembly files the convention is that labels start in column 0, while instructions start in column 8 (1 tab stop).

+++ b/gas/testsuite/gas/aarch64/advsimd-lut.d
@@ -0,0 +1,32 @@
+#objdump: -dr
+#as: -march=armv8-a+lut
+
+.*:     file format .*
+
+Disassembly of section \.text:
+
+0+ <.*>:
+   0:	4e801000 	luti2	v0.16b, \{v0.16b\}, v0\[0\]
+   4:	4e80101f 	luti2	v31.16b, \{v0.16b\}, v0\[0\]
+   8:	4e8013e0 	luti2	v0.16b, \{v31.16b\}, v0\[0\]
...
   ^^
We normally remove the address component from the dump files (use a regexp), so that inserting (or removing) lines does not cause churn on the testsuite.

Otherwise this looks OK.