[PATCH] libgccjit: Improve doc and comments regarding type casts (Was: Clarifying the permitted type conversions)

[Andrea Corallo <andrea.corallo@arm.com>]

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Alex Coplan <Alex.Coplan@arm.com> writes:

> Secondly, I wanted to clarify the situation with respect to explicit
> casts; that is, those conversions allowed by gcc_jit_context_new_cast().
> The docs [0] say:
>
> Currently only a limited set of conversions are possible:
>  - int <-> float
>  - int <-> bool
>  - P* <-> Q*, for pointer types P and Q
>
> However, empirically (at least on aarch64), libgccjit appears to allow
> me to compile casts between any pair of types in the following set
> without any complaint:
>
> {
>   SIGNED_CHAR,
>   UNSIGNED_CHAR,
>   SHORT,
>   UNSIGNED_SHORT,
>   INT,
>   UNSIGNED_INT,
>   LONG,
>   UNSIGNED_LONG,
>   LONG_LONG,
>   UNSIGNED_LONG_LONG
> }

Hi Alex,

Looking at the code I believe all these casts are meant to be supported
(read your intuition was correct).

Also IMO source of confusion is that the doc is mentioning 'int' and
'float' but I believe would be better to have like 'integral' and
'floating-point' to clearly disambiguates with respect to the C
types.

AFAIU the set of supported casts should be like:

     integral       <-> integral
     floating-point <-> floating-point
     integral       <-> floating-point
     integral       <-> bool
     P*             <-> Q*   for pointer types P and Q.

I'd propose to install the following patch to make doc and comments
homogeneous at documenting what do we accept, and I guess we should just
consider bugs if some of these conversions is not handled correctly or
leads to ICE.

Bests

  Andrea

gcc/jit/ChangeLog

2020-07-21  Andrea Corallo  <andrea.corallo@arm.com>

	* docs/_build/texinfo/libgccjit.texi (Type-coercion): Improve doc
	on allowed type casting.
	* docs/topics/expressions.rst (gccjit::context::new_cast)
	(gcc_jit_context_new_cast): Likewise.
	* libgccjit.c: Improve comment on allowed type casting.
	* libgccjit.h: Likewise


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From 914b9e86808c947d4bb2b06c6960fd8031125f67 Mon Sep 17 00:00:00 2001
From: Andrea Corallo <andrea.corallo@arm.com>
Date: Tue, 21 Jul 2020 20:12:23 +0200
Subject: [PATCH] libgccjit: improve documentation on type conversions

gcc/jit/ChangeLog

2020-07-21  Andrea Corallo  <andrea.corallo@arm.com>

	* docs/_build/texinfo/libgccjit.texi (Type-coercion): Improve doc
	on allowed type casting.
	* docs/topics/expressions.rst (gccjit::context::new_cast)
	(gcc_jit_context_new_cast): Likewise.
	* libgccjit.c: Improve comment on allowed type casting.
	* libgccjit.h: Likewise
---
 gcc/jit/docs/_build/texinfo/libgccjit.texi | 30 +++++++++++++++-------
 gcc/jit/docs/topics/expressions.rst        |  8 +++---
 gcc/jit/libgccjit.c                        |  8 +++---
 gcc/jit/libgccjit.h                        |  7 +++--
 4 files changed, 36 insertions(+), 17 deletions(-)

diff --git a/gcc/jit/docs/_build/texinfo/libgccjit.texi b/gcc/jit/docs/_build/texinfo/libgccjit.texi
index 1e14be010426..b170f24d1bb1 100644
--- a/gcc/jit/docs/_build/texinfo/libgccjit.texi
+++ b/gcc/jit/docs/_build/texinfo/libgccjit.texi
@@ -6685,13 +6685,19 @@ Currently only a limited set of conversions are possible:
 @itemize *
 
 @item 
-int <-> float
+integral       <-> integral
 
 @item 
-int <-> bool
+floating-point <-> floating-point
 
 @item 
-P*  <-> Q*, for pointer types P and Q
+integral       <-> floating-point
+
+@item 
+integral       <-> bool
+
+@item 
+P*             <-> Q*   for pointer types P and Q
 @end itemize
 @end quotation
 @end deffn
@@ -12964,14 +12970,20 @@ Currently only a limited set of conversions are possible:
 
 @itemize *
 
-@item 
-int <-> float
+@item
+integral       <-> integral
 
-@item 
-int <-> bool
+@item
+floating-point <-> floating-point
 
-@item 
-P*  <-> Q*, for pointer types P and Q
+@item
+integral       <-> floating-point
+
+@item
+integral       <-> bool
+
+@item
+P*             <-> Q*, for pointer types P and Q
 @end itemize
 @end quotation
 @end deffn
diff --git a/gcc/jit/docs/topics/expressions.rst b/gcc/jit/docs/topics/expressions.rst
index d783ceea51a8..051cee5db211 100644
--- a/gcc/jit/docs/topics/expressions.rst
+++ b/gcc/jit/docs/topics/expressions.rst
@@ -504,9 +504,11 @@ Type-coercion
 
    Currently only a limited set of conversions are possible:
 
-     * int <-> float
-     * int <-> bool
-     * P*  <-> Q*, for pointer types P and Q
+     * integral       <-> integral
+     * floating-point <-> floating-point
+     * integral       <-> floating-point
+     * integral       <-> bool
+     * P*             <-> Q*   for pointer types P and Q
 
 Lvalues
 -------
diff --git a/gcc/jit/libgccjit.c b/gcc/jit/libgccjit.c
index 3d04f6db3aff..403233d5577a 100644
--- a/gcc/jit/libgccjit.c
+++ b/gcc/jit/libgccjit.c
@@ -1629,9 +1629,11 @@ gcc_jit_context_new_call_through_ptr (gcc_jit_context *ctxt,
 
    We only permit these kinds of cast:
 
-     int <-> float
-     int <-> bool
-     P*  <-> Q*   for pointer types P and Q.  */
+     integral       <-> integral
+     floating-point <-> floating-point
+     integral       <-> floating-point
+     integral       <-> bool
+     P*             <-> Q*   for pointer types P and Q.  */
 
 static bool
 is_valid_cast (gcc::jit::recording::type *src_type,
diff --git a/gcc/jit/libgccjit.h b/gcc/jit/libgccjit.h
index 1c5a12e9c015..228befa896d7 100644
--- a/gcc/jit/libgccjit.h
+++ b/gcc/jit/libgccjit.h
@@ -996,8 +996,11 @@ gcc_jit_context_new_call_through_ptr (gcc_jit_context *ctxt,
 /* Type-coercion.
 
    Currently only a limited set of conversions are possible:
-     int <-> float
-     int <-> bool  */
+     integral       <-> integral
+     floating-point <-> floating-point
+     integral       <-> floating-point
+     integral       <-> bool
+     P*             <-> Q*   for pointer types P and Q.  */
 extern gcc_jit_rvalue *
 gcc_jit_context_new_cast (gcc_jit_context *ctxt,
 			  gcc_jit_location *loc,
-- 
2.17.1