i386: Add "Ws" constraint for symbolic address/label reference [PR105576]
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Commit Message
Printing the raw symbol is useful in inline asm (e.g. in C++ to get the
mangled name). Similar constraints are available in other targets (e.g.
"S" for aarch64/riscv, "Cs" for m68k).
There isn't a good way for x86 yet, e.g. "i" doesn't work for
PIC/-mcmodel=large. This patch adds "Ws". Here are possible use cases:
```
namespace ns { extern int var; }
asm (".pushsection .xxx,\"aw\"; .dc.a %0; .popsection" :: "Ws"(&var));
asm (".reloc ., BFD_RELOC_NONE, %0" :: "Ws"(&var));
```
gcc/ChangeLog:
PR target/105576
* config/i386/constraints.md: Define constraint "Ws".
* doc/md.texi: Document it.
gcc/testsuite/ChangeLog:
* gcc.target/i386/asm-raw-symbol.c: New testcase.
---
This obsoletes https://gcc.gnu.org/pipermail/gcc-patches/2024-January/642580.html
I initially tried 'z', but Uros requested that a W prefix is used.
---
gcc/config/i386/constraints.md | 4 ++++
gcc/doc/md.texi | 4 ++++
gcc/testsuite/gcc.target/i386/asm-raw-symbol.c | 13 +++++++++++++
3 files changed, 21 insertions(+)
create mode 100644 gcc/testsuite/gcc.target/i386/asm-raw-symbol.c
Comments
On Thu, Jan 11, 2024 at 10:24 AM Fangrui Song <maskray@google.com> wrote:
>
> Printing the raw symbol is useful in inline asm (e.g. in C++ to get the
> mangled name). Similar constraints are available in other targets (e.g.
> "S" for aarch64/riscv, "Cs" for m68k).
>
> There isn't a good way for x86 yet, e.g. "i" doesn't work for
> PIC/-mcmodel=large. This patch adds "Ws". Here are possible use cases:
>
> ```
> namespace ns { extern int var; }
> asm (".pushsection .xxx,\"aw\"; .dc.a %0; .popsection" :: "Ws"(&var));
> asm (".reloc ., BFD_RELOC_NONE, %0" :: "Ws"(&var));
> ```
>
> gcc/ChangeLog:
>
> PR target/105576
> * config/i386/constraints.md: Define constraint "Ws".
> * doc/md.texi: Document it.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/i386/asm-raw-symbol.c: New testcase.
>
> ---
>
> This obsoletes https://gcc.gnu.org/pipermail/gcc-patches/2024-January/642580.html
> I initially tried 'z', but Uros requested that a W prefix is used.
> ---
> gcc/config/i386/constraints.md | 4 ++++
> gcc/doc/md.texi | 4 ++++
> gcc/testsuite/gcc.target/i386/asm-raw-symbol.c | 13 +++++++++++++
> 3 files changed, 21 insertions(+)
> create mode 100644 gcc/testsuite/gcc.target/i386/asm-raw-symbol.c
Thanks to Uros for "W" prefix suggestion.
If "Ws" sounds a good choice, I'll go ahead with my Clang patch adding
"Ws", even if the GCC patch is still pending:)
https://github.com/protocolbuffers/protobuf/blob/1fe463ce71b6acc60b3aef65d51185e3704cac8b/src/google/protobuf/stubs/common.h
// Strongly references the given variable such that the linker will be forced
// to pull in this variable's translation unit.
template <typename T>
void StrongReference(const T& var) {
auto volatile unused = &var;
(void)&unused; // Use address to avoid an extra load of "unused".
}
is an example that "Ws" constraint (which expands to no instruction)
works better than the volatile address-taken operation.
I am not so familiar with the mechanism, but StrongReference is used
to establish a dependency edge so that the ld --gc-sections will not
garbage `var`.
On Thu, Jan 11, 2024 at 7:24 PM Fangrui Song <maskray@google.com> wrote:
>
> Printing the raw symbol is useful in inline asm (e.g. in C++ to get the
> mangled name). Similar constraints are available in other targets (e.g.
> "S" for aarch64/riscv, "Cs" for m68k).
>
> There isn't a good way for x86 yet, e.g. "i" doesn't work for
> PIC/-mcmodel=large. This patch adds "Ws". Here are possible use cases:
>
> ```
> namespace ns { extern int var; }
> asm (".pushsection .xxx,\"aw\"; .dc.a %0; .popsection" :: "Ws"(&var));
> asm (".reloc ., BFD_RELOC_NONE, %0" :: "Ws"(&var));
> ```
>
> gcc/ChangeLog:
>
> PR target/105576
> * config/i386/constraints.md: Define constraint "Ws".
> * doc/md.texi: Document it.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/i386/asm-raw-symbol.c: New testcase.
OK.
Thanks,
Uros.
>
> ---
>
> This obsoletes https://gcc.gnu.org/pipermail/gcc-patches/2024-January/642580.html
> I initially tried 'z', but Uros requested that a W prefix is used.
> ---
> gcc/config/i386/constraints.md | 4 ++++
> gcc/doc/md.texi | 4 ++++
> gcc/testsuite/gcc.target/i386/asm-raw-symbol.c | 13 +++++++++++++
> 3 files changed, 21 insertions(+)
> create mode 100644 gcc/testsuite/gcc.target/i386/asm-raw-symbol.c
>
> diff --git a/gcc/config/i386/constraints.md b/gcc/config/i386/constraints.md
> index 0c6e662df25..280e4c8e36c 100644
> --- a/gcc/config/i386/constraints.md
> +++ b/gcc/config/i386/constraints.md
> @@ -348,6 +348,10 @@ (define_constraint "Wf"
> to double word size."
> (match_operand 0 "x86_64_dwzext_immediate_operand"))
>
> +(define_constraint "Ws"
> + "A symbolic reference or label reference."
> + (match_code "const,symbol_ref,label_ref"))
> +
> (define_constraint "Z"
> "32-bit unsigned integer constant, or a symbolic reference known
> to fit that range (for immediate operands in zero-extending x86-64
> diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
> index 47a87d6ceec..b0c61925120 100644
> --- a/gcc/doc/md.texi
> +++ b/gcc/doc/md.texi
> @@ -4275,6 +4275,10 @@ require non-@code{VOIDmode} immediate operands).
> 128-bit integer constant where both the high and low 64-bit word
> satisfy the @code{e} constraint.
>
> +@item Ws
> +A symbolic reference or label reference.
> +You can use the @code{%p} modifier to print the raw symbol.
> +
> @item Z
> 32-bit unsigned integer constant, or a symbolic reference known
> to fit that range (for immediate operands in zero-extending x86-64
> diff --git a/gcc/testsuite/gcc.target/i386/asm-raw-symbol.c b/gcc/testsuite/gcc.target/i386/asm-raw-symbol.c
> new file mode 100644
> index 00000000000..b7854567dd9
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/asm-raw-symbol.c
> @@ -0,0 +1,13 @@
> +/* { dg-do compile } */
> +
> +extern int var;
> +
> +void
> +func (void)
> +{
> + __asm__ ("@ %p0" : : "Ws" (func));
> + __asm__ ("@ %p0" : : "Ws" (&var + 1));
> +}
> +
> +/* { dg-final { scan-assembler "@ func" } } */
> +/* { dg-final { scan-assembler "@ var\\+4" } } */
> --
> 2.43.0.275.g3460e3d667-goog
>
On Tue, Jan 16, 2024 at 11:47 PM Uros Bizjak <ubizjak@gmail.com> wrote:
>
> On Thu, Jan 11, 2024 at 7:24 PM Fangrui Song <maskray@google.com> wrote:
> >
> > Printing the raw symbol is useful in inline asm (e.g. in C++ to get the
> > mangled name). Similar constraints are available in other targets (e.g.
> > "S" for aarch64/riscv, "Cs" for m68k).
> >
> > There isn't a good way for x86 yet, e.g. "i" doesn't work for
> > PIC/-mcmodel=large. This patch adds "Ws". Here are possible use cases:
> >
> > ```
> > namespace ns { extern int var; }
> > asm (".pushsection .xxx,\"aw\"; .dc.a %0; .popsection" :: "Ws"(&var));
> > asm (".reloc ., BFD_RELOC_NONE, %0" :: "Ws"(&var));
> > ```
> >
> > gcc/ChangeLog:
> >
> > PR target/105576
> > * config/i386/constraints.md: Define constraint "Ws".
> > * doc/md.texi: Document it.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.target/i386/asm-raw-symbol.c: New testcase.
>
> OK.
Hi Fangrui,
I pushed it for you with indentation changes in the commit log.
Thanks.
> Thanks,
> Uros.
>
> >
> > ---
> >
> > This obsoletes https://gcc.gnu.org/pipermail/gcc-patches/2024-January/642580.html
> > I initially tried 'z', but Uros requested that a W prefix is used.
> > ---
> > gcc/config/i386/constraints.md | 4 ++++
> > gcc/doc/md.texi | 4 ++++
> > gcc/testsuite/gcc.target/i386/asm-raw-symbol.c | 13 +++++++++++++
> > 3 files changed, 21 insertions(+)
> > create mode 100644 gcc/testsuite/gcc.target/i386/asm-raw-symbol.c
> >
> > diff --git a/gcc/config/i386/constraints.md b/gcc/config/i386/constraints.md
> > index 0c6e662df25..280e4c8e36c 100644
> > --- a/gcc/config/i386/constraints.md
> > +++ b/gcc/config/i386/constraints.md
> > @@ -348,6 +348,10 @@ (define_constraint "Wf"
> > to double word size."
> > (match_operand 0 "x86_64_dwzext_immediate_operand"))
> >
> > +(define_constraint "Ws"
> > + "A symbolic reference or label reference."
> > + (match_code "const,symbol_ref,label_ref"))
> > +
> > (define_constraint "Z"
> > "32-bit unsigned integer constant, or a symbolic reference known
> > to fit that range (for immediate operands in zero-extending x86-64
> > diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
> > index 47a87d6ceec..b0c61925120 100644
> > --- a/gcc/doc/md.texi
> > +++ b/gcc/doc/md.texi
> > @@ -4275,6 +4275,10 @@ require non-@code{VOIDmode} immediate operands).
> > 128-bit integer constant where both the high and low 64-bit word
> > satisfy the @code{e} constraint.
> >
> > +@item Ws
> > +A symbolic reference or label reference.
> > +You can use the @code{%p} modifier to print the raw symbol.
> > +
> > @item Z
> > 32-bit unsigned integer constant, or a symbolic reference known
> > to fit that range (for immediate operands in zero-extending x86-64
> > diff --git a/gcc/testsuite/gcc.target/i386/asm-raw-symbol.c b/gcc/testsuite/gcc.target/i386/asm-raw-symbol.c
> > new file mode 100644
> > index 00000000000..b7854567dd9
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.target/i386/asm-raw-symbol.c
> > @@ -0,0 +1,13 @@
> > +/* { dg-do compile } */
> > +
> > +extern int var;
> > +
> > +void
> > +func (void)
> > +{
> > + __asm__ ("@ %p0" : : "Ws" (func));
> > + __asm__ ("@ %p0" : : "Ws" (&var + 1));
> > +}
> > +
> > +/* { dg-final { scan-assembler "@ func" } } */
> > +/* { dg-final { scan-assembler "@ var\\+4" } } */
> > --
> > 2.43.0.275.g3460e3d667-goog
> >
@@ -348,6 +348,10 @@ (define_constraint "Wf"
to double word size."
(match_operand 0 "x86_64_dwzext_immediate_operand"))
+(define_constraint "Ws"
+ "A symbolic reference or label reference."
+ (match_code "const,symbol_ref,label_ref"))
+
(define_constraint "Z"
"32-bit unsigned integer constant, or a symbolic reference known
to fit that range (for immediate operands in zero-extending x86-64
@@ -4275,6 +4275,10 @@ require non-@code{VOIDmode} immediate operands).
128-bit integer constant where both the high and low 64-bit word
satisfy the @code{e} constraint.
+@item Ws
+A symbolic reference or label reference.
+You can use the @code{%p} modifier to print the raw symbol.
+
@item Z
32-bit unsigned integer constant, or a symbolic reference known
to fit that range (for immediate operands in zero-extending x86-64
new file mode 100644
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+
+extern int var;
+
+void
+func (void)
+{
+ __asm__ ("@ %p0" : : "Ws" (func));
+ __asm__ ("@ %p0" : : "Ws" (&var + 1));
+}
+
+/* { dg-final { scan-assembler "@ func" } } */
+/* { dg-final { scan-assembler "@ var\\+4" } } */