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gccrs: Support some LLVM builtin functions - #4809

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Polygonalr:llvm-extern2
Aug 31, 2026
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gccrs: Support some LLVM builtin functions#4809
philberty merged 4 commits into
Rust-GCC:masterfrom
Polygonalr:llvm-extern2

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@Polygonalr

@Polygonalr Polygonalr commented Aug 23, 2026 •
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Closes #4818, currently it only supports the rdrand and rdseed functions, I'll need to write more function adapters to support other LLVM built-ins.

In theory it should support all the LLVM built-ins used in stdarch, though llvm.x86.vcvtph2ps and llvm.x86.vcvtps2ph requires the SIMD types to be compiled as well (which will also be compiled as part of core_arch within stdarch).

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Polygonalr marked this pull request as draft August 23, 2026 08:07
@powerboat9

powerboat9 commented Aug 23, 2026

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Could you replace "frontend" in your first commit with "front end"? Also, you should probably replace the mention of (BuiltinsContext) with a mention of (BuiltinsContext::get) and a (BuiltinsContext::BuiltinsContext): Likewise..

@Polygonalr
gccrs: Make gcc targetm builtins available to the Rust front end
e5b56bd 
This is part of making LLVM builtins work for gccrs.

gcc/rust/ChangeLog:

	* backend/rust-builtins.h (BuiltinsContext::SetupState): New enum.
	* backend/rust-builtins.cc (BuiltinsContext::get): Ensure that BuiltinsContext is only
	initialized once.
	(BuiltinsContext::BuiltinsContext): Likewise.
	(BuiltinsContext::setup): Call targetm.init_builtins to make GCC builtins available
	to the frontend.
	* rust-gcc.cc (init): Eagerly initialize BuiltinsContext.

Signed-Off-By: Yap Zhi Heng <yapzhhg@gmail.com>
@Polygonalr Polygonalr mentioned this pull request Aug 25, 2026
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@Polygonalr
Polygonalr force-pushed the llvm-extern2 branch 3 times, most recently from 781077d to a19832f Compare August 29, 2026 06:25
@Polygonalr
gccrs: Initial implementation of LLVM builtin to GCC adapter
ef8e125 
Only works for rdseed, rdrand, addcarry and subborrow for now. Compiled 006t.original output
from compiling llvm_builtins.rs:

```
struct (u16, i32) x86_rdrand16_step ()
{
  u16 RUSTTMP.0;
  i32 RUSTTMP.1;

  RUSTTMP.1 = __builtin_ia32_rdrand16_step (&RUSTTMP.0);
  return {.__0=RUSTTMP.0, .__1=RUSTTMP.1};
}

struct (u32, i32) x86_rdrand32_step ()
{
  u32 RUSTTMP.2;
  i32 RUSTTMP.3;

  RUSTTMP.3 = __builtin_ia32_rdrand32_step (&RUSTTMP.2);
  return {.__0=RUSTTMP.2, .__1=RUSTTMP.3};
}

struct (u64, i32) x86_rdrand64_step ()
{
  u64 RUSTTMP.4;
  i32 RUSTTMP.5;

  RUSTTMP.5 = __builtin_ia32_rdrand64_step ((unsigned long *) &RUSTTMP.4);
  return {.__0=RUSTTMP.4, .__1=RUSTTMP.5};
}

struct (u16, i32) x86_rdseed16_step ()
{
  u16 RUSTTMP.6;
  i32 RUSTTMP.7;

  RUSTTMP.7 = __builtin_ia32_rdseed_hi_step (&RUSTTMP.6);
  return {.__0=RUSTTMP.6, .__1=RUSTTMP.7};
}

struct (u32, i32) x86_rdseed32_step ()
{
  u32 RUSTTMP.8;
  i32 RUSTTMP.9;

  RUSTTMP.9 = __builtin_ia32_rdseed_si_step (&RUSTTMP.8);
  return {.__0=RUSTTMP.8, .__1=RUSTTMP.9};
}

struct (u64, i32) x86_rdseed64_step ()
{
  u64 RUSTTMP.10;
  i32 RUSTTMP.11;

  RUSTTMP.11 = __builtin_ia32_rdseed_di_step ((unsigned long *) &RUSTTMP.10);
  return {.__0=RUSTTMP.10, .__1=RUSTTMP.11};
}

struct (u8, u32) llvm_addcarry_u32 (const u8 a, const u32 b, const u32 c)
{
  u32 RUSTTMP.12;
  u8 RUSTTMP.13;

  RUSTTMP.13 = (u8) __builtin_ia32_addcarryx_u32 ((unsigned char) a, (u32) b, (u32) c, &RUSTTMP.12);
  return {.__0=RUSTTMP.13, .__1=RUSTTMP.12};
}

struct (u8, u32) llvm_subborrow_u32 (const u8 a, const u32 b, const u32 c)
{
  u32 RUSTTMP.14;
  u8 RUSTTMP.15;

  RUSTTMP.15 = (u8) __builtin_ia32_sbb_u32 ((unsigned char) a, (u32) b, (u32) c, &RUSTTMP.14);
  return {.__0=RUSTTMP.15, .__1=RUSTTMP.14};
}

struct (u8, u64) llvm_addcarry_u64 (const u8 a, const u64 b, const u64 c)
{
  u64 RUSTTMP.16;
  u8 RUSTTMP.17;

  RUSTTMP.17 = (u8) __builtin_ia32_addcarryx_u64 ((unsigned char) a, (unsigned long) b, (unsigned long) c, (unsigned long *) &RUSTTMP.16);
  return {.__0=RUSTTMP.17, .__1=RUSTTMP.16};
}

struct (u8, u64) llvm_subborrow_u64 (const u8 a, const u64 b, const u64 c)
{
  u64 RUSTTMP.18;
  u8 RUSTTMP.19;

  RUSTTMP.19 = (u8) __builtin_ia32_sbb_u64 ((unsigned char) a, (unsigned long) b, (unsigned long) c, (unsigned long *) &RUSTTMP.18);
  return {.__0=RUSTTMP.19, .__1=RUSTTMP.18};
}
```

gcc/rust/ChangeLog:

	* backend/rust-builtins.h (LlvmBuiltinMappingResult): New enum.
	(LlvmBuiltinAdapter): New enum.
	(LlvmBuiltinMapping): New enum.
	(BuiltinsContext::map_llvm_to_gcc_builtin): New function for LLVM built-in mapping.
	(BuiltinsContext::register_builtin): New function for registering built-ins.
	(BuiltinsContext::register_llvm_to_gcc_builtin): New function.
	(BuiltinsContext::llvm_to_gcc_builtin): New map to translate function names.
	* backend/rust-builtins.cc (BuiltinsContext::map_llvm_to_gcc_builtin): Implementation.
	(BuiltinsContext::register_llvm_to_gcc_builtin): Implementation.
	(BuiltinsContext::register_builtin): Implementation.
	(BuiltinsContext::setup): Call register_llvm_to_gcc_builtin during setup.
	* rust-lang.cc (grs_langhook_builtin_function): Register GCC built-in functions.
	* backend/rust-compile-extern.h (CompileExternItem::OutputTupleOrder): New enum to denote
	the tuple field order of the LLVM built-in's return type.
	(CompileExternItem::compile_x86_output_pointer_adapter): New function to adapt LLVM's
	rdseed, rdrand, addcarry, subborrow function signatures to GCC's equivalents.
	(CompileExternItem::visit (HIR::ExternalFunctionItem)): Handle UNADJUSTED ABI case by
	properly resolving LLVM intrinsic function names.

Signed-off-by: Yap Zhi Heng <yapzhhg@gmail.com>
@Polygonalr
gccrs: Implement 1-to-1 adapters for compiling LLVM built-ins signatu…
8b93619 
…res with GCC built-ins

Similar to the previous commit, but for FORWARD_ARGUMENTS cases in CompileExternItem::visit
(ExternalFunctionItem). Compiled 006t.original output from compiling llvm_builtins.rs for only
the enabled FORWARD_ARGUMENT cases ():

```
u8 llvm_addcarryx_u32 (const u8 a, const u32 b, const u32 c, u8 * const {ref-all} d)
{
  return (u8) __builtin_ia32_addcarryx_u32 ((unsigned char) a, (u32) b, (u32) c, (u32 *) d);
}

u8 llvm_addcarryx_u64 (const u8 a, const u64 b, const u64 c, u8 * const {ref-all} d)
{
  return (u8) __builtin_ia32_addcarryx_u64 ((unsigned char) a, (unsigned long) b, (unsigned long) c, (unsigned long *) d);
}
```

vcvtph2ps and vcvtps2ph functions are not supported yet as gccrs doesn't support SIMD types yet.

gcc/rust/ChangeLog:

	* backend/rust-builtins.cc (BuiltinsContext::register_llvm_to_gcc_builtin): Add entries
	for vcvtph2ps & vcvtps2ph cases (currently unused due to the reason mentioned above).
	* backend/rust-compile-extern.h (CompileExternItem::visit(HIR::ExternalFunctionItem)):
	Remove placeholder function in the FORWARD_ARGUMENTS case under compilation of UNADJUSTED
	ABI.
	(CompileExternItem::compile_x86_forwarding_adapter): New function to adapt LLVM's addcarryx
	function signatures by simply forwarding the parameters and return var without changes.

gcc/testsuite/ChangeLog:

	* rust/compile/llvm_builtins.rs: Enable addcarryx cases, add TODO comment for vcvtph2ps &
	vcvtps2ph cases.

Signed-off-by: Yap Zhi Heng <yapzhhg@gmail.com>
@Polygonalr
Polygonalr marked this pull request as ready for review August 29, 2026 08:27
@Polygonalr

Polygonalr commented Aug 29, 2026

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Tests are not final yet.

  • It seems like tests on the 32-bit arches are failing due to not having 64-bit built-ins such as __builtin_ia32_rdrand64_step and __builtin_ia32_rdseed_di_step, wondering if I should remove them or find a way to exclude these functions from the 32-bit arches.
  • I'll also need to include some dg-final directives in my tests similar to what I did in #[repr(transparent)] initial implementation #4650.

@powerboat9

powerboat9 commented Aug 29, 2026

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I think the test should probably be restricted to run only on x86_64

@Polygonalr
Polygonalr force-pushed the llvm-extern2 branch 2 times, most recently from 3329098 to e92e3a6 Compare August 30, 2026 11:43
@Polygonalr
gccrs: Update llvm_builtins test cases
5264698 
gcc/testsuite/ChangeLog:

	* rust/compile/llvm_builtins.rs: Removed 64-bit functions, ensure main calls all llvm
	built-ins, add dg-final directives to check the generated tree dump, ensure the test
	only gets compiled on x86 targets.
	* rust/compile/llvm_builtins_64_bit.rs: New test derived from llvm_builtins.rs, but
	for 64-bit functions.

Signed-off-by: Yap Zhi Heng <yapzhhg@gmail.com>
philberty
philberty approved these changes Aug 30, 2026
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LGTM

philberty
philberty reviewed Aug 30, 2026
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Comment thread gcc/testsuite/rust/compile/llvm_builtins.rs
#[link_name = "llvm.x86.subborrow.32"]
fn llvm_subborrow_u32(a: u8, b: u32, c: u32) -> (u8, u32);

// TODO implement the SIMD types (i16x8, f32x4, f32x8) before

@philberty philberty Aug 30, 2026

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repr simd should be there they will be VECTOR_TYPES which are basically structs in a lot of ways

@philberty
philberty added this pull request to the merge queue Aug 31, 2026
Merged via the queue into Rust-GCC:master with commit 63ea23d Aug 31, 2026
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Compile UNADJUSTED ABI extern functions

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@Polygonalr @powerboat9 @philberty