Hi all,

Previously we had experienced issues with assembling a "VCVTNE" instruction
in the presence of the MVE architecture extension, because it could be
interpreted both as:

* The base instruction VCVT + NE for IT predication when inside an IT block.
* The MVE instruction VCVTN + E in the Else of a VPT block.

Given a C reproducer of:
```
int test_function(float value)
{
     int ret_val = 10;
     if (value != 0.0)
     {
       ret_val = (int) value;
     }
     return ret_val;
}
```
GCC generates a VCVTNE instruction based on the `truncsisf2_vfp`
pattern, which will look like:
`vcvtne.s32.f32 s-reg, s-reg`
This still triggers an error due to being misidentified as "vcvtn+e"
Similar errors were found with other type combinations and instruction
patterns (these have all been added to the testing of this patch).

This class of errors was previously worked around by:
https://sourceware.org/pipermail/binutils/2020-August/112728.html
which addressed this by looking at the operand types, however,
that isn't adequate to cover all the extra cases that have been
found.  Instead, we add some special-casing logic earlier when
the instructions are parsed that is conditional on whether we are
in a VPT block or not, when the instruction is parsed.

Note that in the follo-up 2/2 patch I have done a find n replace
to change the misleading error message mentioning ARMv8.2.

gas/ChangeLog:

       * config/tc-arm.c (opcode_lookup): Add special vcvtn handling.
       * testsuite/gas/arm/mve-vcvtne-it-bad.l: Add further testing.
       * testsuite/gas/arm/mve-vcvtne-it-bad.s: Likewise.
       * testsuite/gas/arm/mve-vcvtne-it.d: Likewise.
       * testsuite/gas/arm/mve-vcvtne-it.s: Likewise.


Inline copy of patch:

diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
index 
2e6d175482efe4bc58a2e277bd2cc4c48f9e1863..25506241f29cdb0db169bb7801604ea4e356989c 
100644
--- a/gas/config/tc-arm.c
+++ b/gas/config/tc-arm.c
@@ -19143,16 +19143,6 @@ do_neon_cvt_1 (enum neon_cvt_mode mode)
         return;
       }

-  if ((rs == NS_FD || rs == NS_QQI) && mode == neon_cvt_mode_n
-      && ARM_CPU_HAS_FEATURE (cpu_variant, mve_ext))
-    {
-      /* We are dealing with vcvt with the 'ne' condition.  */
-      inst.cond = 0x1;
-      inst.instruction = N_MNEM_vcvt;
-      do_neon_cvt_1 (neon_cvt_mode_z);
-      return;
-    }
-
     /* VFP rather than Neon conversions.  */
     if (flavour >= neon_cvt_flavour_first_fp)
       {
@@ -22748,6 +22738,23 @@ opcode_lookup (char **str)
        cond = (const struct asm_cond *) str_hash_find_n (arm_vcond_hsh, 
affix, 1);
        opcode = (const struct asm_opcode *) str_hash_find_n 
(arm_ops_hsh, base,
   							   affix - base);
+
+     /* A known edge case is a conflict between an 'e' as a suffix for an
+	Else of a VPT predication block and an 'ne' suffix for an IT block.
+	If we detect that edge case here and we are not in a VPT VECTOR_PRED
+	block, reset opcode and cond, so that the 'ne' case can be detected
+	in the next section for 2-character conditional suffixes.
+	An example where this is a problem is between the MVE 'vcvtn' and the
+	non-MVE 'vcvt' instructions. */
+     if (cond && opcode
+	 && cond->template_name[0] == 'e'
+	 && opcode->template_name[affix - base - 1] == 'n'
+	 && now_pred.type != VECTOR_PRED)
+       {
+	 opcode = NULL;
+	 cond = NULL;
+       }
+
        /* If this opcode can not be vector predicated then don't accept 
it with a
   	vector predication code.  */
        if (opcode && !opcode->mayBeVecPred)
diff --git a/gas/testsuite/gas/arm/mve-vcvtne-it-bad.l 
b/gas/testsuite/gas/arm/mve-vcvtne-it-bad.l
index 
8765ae0d6912e322ecabfb215f5401327fa97cbe..ca57a38537c62926f43119c1e9abd9dbaf549a1b 
100644
--- a/gas/testsuite/gas/arm/mve-vcvtne-it-bad.l
+++ b/gas/testsuite/gas/arm/mve-vcvtne-it-bad.l
@@ -1,2 +1,17 @@
   [^:]*: Assembler messages:
   [^:]*:3: Error: thumb conditional instruction should be in IT block 
-- `vcvtne.s32.f64 s13,d8'
+[^:]*:4: Error: thumb conditional instruction should be in IT block -- 
`vcvtne.u32.f64 s13,d8'
+[^:]*:5: Error: thumb conditional instruction should be in IT block -- 
`vcvtne.s32.f32 s13,s8'
+[^:]*:6: Error: thumb conditional instruction should be in IT block -- 
`vcvtne.u32.f32 s13,s8'
+[^:]*:7: Warning: ARMv8.2 scalar fp16 instruction cannot be 
conditional, the behaviour is UNPREDICTABLE
+[^:]*:7: Error: thumb conditional instruction should be in IT block -- 
`vcvtne.s32.f16 s13,s8'
+[^:]*:8: Warning: ARMv8.2 scalar fp16 instruction cannot be 
conditional, the behaviour is UNPREDICTABLE
+[^:]*:8: Error: thumb conditional instruction should be in IT block -- 
`vcvtne.u32.f16 s13,s8'
+[^:]*:9: Error: thumb conditional instruction should be in IT block -- 
`vcvtne.f64.s32 d13,s8'
+[^:]*:10: Error: thumb conditional instruction should be in IT block -- 
`vcvtne.f64.u32 d13,s8'
+[^:]*:11: Error: thumb conditional instruction should be in IT block -- 
`vcvtne.f32.s32 s13,s8'
+[^:]*:12: Error: thumb conditional instruction should be in IT block -- 
`vcvtne.f32.u32 s13,s8'
+[^:]*:13: Warning: ARMv8.2 scalar fp16 instruction cannot be 
conditional, the behaviour is UNPREDICTABLE
+[^:]*:13: Error: thumb conditional instruction should be in IT block -- 
`vcvtne.f16.s32 s13,s8'
+[^:]*:14: Warning: ARMv8.2 scalar fp16 instruction cannot be 
conditional, the behaviour is UNPREDICTABLE
+[^:]*:14: Error: thumb conditional instruction should be in IT block -- 
`vcvtne.f16.u32 s13,s8'
diff --git a/gas/testsuite/gas/arm/mve-vcvtne-it-bad.s 
b/gas/testsuite/gas/arm/mve-vcvtne-it-bad.s
index 
e4c1b99906536c3c6cc8334e98d84cd170c19d76..b7d83f6fe0dfd4140b6cc11cf748d43787e932ba 
100644
--- a/gas/testsuite/gas/arm/mve-vcvtne-it-bad.s
+++ b/gas/testsuite/gas/arm/mve-vcvtne-it-bad.s
@@ -1,3 +1,14 @@
   .syntax unified
   .text
   vcvtne.s32.f64	s13, d8
+vcvtne.u32.f64	s13, d8
+vcvtne.s32.f32	s13, s8
+vcvtne.u32.f32	s13, s8
+vcvtne.s32.f16	s13, s8
+vcvtne.u32.f16	s13, s8
+vcvtne.f64.s32	d13, s8
+vcvtne.f64.u32	d13, s8
+vcvtne.f32.s32	s13, s8
+vcvtne.f32.u32	s13, s8
+vcvtne.f16.s32	s13, s8
+vcvtne.f16.u32	s13, s8
diff --git a/gas/testsuite/gas/arm/mve-vcvtne-it.d 
b/gas/testsuite/gas/arm/mve-vcvtne-it.d
index 
2bc069a77e5a46d83dd42d658b2d79a53e9da593..27e45753c6497fec85ee194e9ebae4a3fdbeee0f 
100644
--- a/gas/testsuite/gas/arm/mve-vcvtne-it.d
+++ b/gas/testsuite/gas/arm/mve-vcvtne-it.d
@@ -1,10 +1,31 @@
   # name: Armv8.1-M Mainline vcvt instruction in it block (with MVE)
   # as: -march=armv8.1-m.main+mve.fp+fp.dp
+#warning: [^:]*: Assembler messages:
+#warning: [^:]*:10: Warning: ARMv8.2 scalar fp16 instruction cannot be 
conditional, the behaviour is UNPREDICTABLE
+#warning: [^:]*:11: Warning: ARMv8.2 scalar fp16 instruction cannot be 
conditional, the behaviour is UNPREDICTABLE
+#warning: [^:]*:19: Warning: ARMv8.2 scalar fp16 instruction cannot be 
conditional, the behaviour is UNPREDICTABLE
+#warning: [^:]*:20: Warning: ARMv8.2 scalar fp16 instruction cannot be 
conditional, the behaviour is UNPREDICTABLE
   # objdump: -dr --prefix-addresses --show-raw-insn -marmv8.1-m.main

   .*: +file format .*arm.*

   Disassembly of section .text:
-^[^>]*> bf18[ 	]+it[ 	]+ne
+^[^>]*> bf1c[ 	]+itt[ 	]+ne
   ^[^>]*> eefd 6bc8[ 	]+vcvtne.s32.f64[ 	]+s13, d8
+^[^>]*> eefc 6bc8[ 	]+vcvtne.u32.f64[ 	]+s13, d8
+^[^>]*> bf1c[ 	]+itt[ 	]+ne
+^[^>]*> eefd 6ac4[ 	]+vcvtne.s32.f32[ 	]+s13, s8
+^[^>]*> eefc 6ac4[ 	]+vcvtne.u32.f32[ 	]+s13, s8
+^[^>]*> bf1c[ 	]+itt[ 	]+ne
+^[^>]*> eefd 69c4[ 	]+vcvtne.s32.f16[ 	]+s13, s8.*
+^[^>]*> eefc 69c4[ 	]+vcvtne.u32.f16[ 	]+s13, s8.*
+^[^>]*> bf1c[ 	]+itt[ 	]+ne
+^[^>]*> eeb8 dbc4[ 	]+vcvtne.f64.s32[ 	]+d13, s8
+^[^>]*> eeb8 db44[ 	]+vcvtne.f64.u32[ 	]+d13, s8
+^[^>]*> bf1c[ 	]+itt[ 	]+ne
+^[^>]*> eef8 6ac4[ 	]+vcvtne.f32.s32[ 	]+s13, s8
+^[^>]*> eef8 6a44[ 	]+vcvtne.f32.u32[ 	]+s13, s8
+^[^>]*> bf1c[ 	]+itt[ 	]+ne
+^[^>]*> eef8 69c4[ 	]+vcvtne.f16.s32[ 	]+s13, s8.*
+^[^>]*> eef8 6944[ 	]+vcvtne.f16.u32[ 	]+s13, s8.*
   #pass
diff --git a/gas/testsuite/gas/arm/mve-vcvtne-it.s 
b/gas/testsuite/gas/arm/mve-vcvtne-it.s
index 
a9f260681283c3c68bace0abaa6754a4cab9c62f..e8be576c2960fc6c2cf3582604c436561099d046 
100644
--- a/gas/testsuite/gas/arm/mve-vcvtne-it.s
+++ b/gas/testsuite/gas/arm/mve-vcvtne-it.s
@@ -1,4 +1,20 @@
   .syntax unified
   .text
-it ne
+itt ne
   vcvtne.s32.f64	s13, d8
+vcvtne.u32.f64	s13, d8
+itt ne
+vcvtne.s32.f32	s13, s8
+vcvtne.u32.f32	s13, s8
+itt ne
+vcvtne.s32.f16	s13, s8
+vcvtne.u32.f16	s13, s8
+itt ne
+vcvtne.f64.s32	d13, s8
+vcvtne.f64.u32	d13, s8
+itt ne
+vcvtne.f32.s32	s13, s8
+vcvtne.f32.u32	s13, s8
+itt ne
+vcvtne.f16.s32	s13, s8
+vcvtne.f16.u32	s13, s8