From 01510f2c922af8629c7a730ef92a31fa83bd9f49 Mon Sep 17 00:00:00 2001 From: Yong He Date: Wed, 15 Oct 2025 20:59:47 -0700 Subject: Immutable access qualifier for pointers and use `__ldg` on cuda. (#8710) This PR implements `Access.Immutable` to allow pointers to immutable data. The new type `ImmutablePtr` is defined as an alias of `Ptr`. By forming a immutable pointer, the programmer is conveying to the compiler that the data at the pointer address will never change during the execution of the current program. Therefore loads from immutable pointers can be deduplicated by the compiler, and will translate to `__ldg` when generating code for CUDA. The SPIRV backend is not changed in this PR, since the current SPIRV spec makes it very difficult to specify loads from immutable address without generating tons of wrappers and boilerplate type declarations. We would like to see the spec evolved a bit to around its support of `NonWritable` physical storage pointers or immutable loads before we attempt to express such immutability in SPIRV. For now we simply emit ordinary pointers and loads when generating spirv. --------- Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com> --- source/slang/slang-emit-spirv.cpp | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) (limited to 'source/slang/slang-emit-spirv.cpp') diff --git a/source/slang/slang-emit-spirv.cpp b/source/slang/slang-emit-spirv.cpp index d5697117a..1b59d3070 100644 --- a/source/slang/slang-emit-spirv.cpp +++ b/source/slang/slang-emit-spirv.cpp @@ -6481,12 +6481,19 @@ struct SPIRVEmitContext : public SourceEmitterBase, public SPIRVEmitSharedContex SpvStorageClassPhysicalStorageBuffer) { // If inst has a pointer type with PhysicalStorageBuffer address space, - // emit AliasedPointer decoration. - emitOpDecorate( - getSection(SpvLogicalSectionID::Annotations), - nullptr, - varInst, - (isVar ? SpvDecorationAliasedPointer : SpvDecorationAliased)); + // emit AliasedPointer or RestrictPointer decoration. + SpvDecoration decor; + if (ptrType->getAccessQualifier() == AccessQualifier::Immutable) + { + // We can always safely use RestrictPointer for immutable pointers. + // This will allow better optimization. + decor = isVar ? SpvDecorationRestrictPointer : SpvDecorationRestrict; + } + else + { + decor = isVar ? SpvDecorationAliasedPointer : SpvDecorationAliased; + } + emitOpDecorate(getSection(SpvLogicalSectionID::Annotations), nullptr, varInst, decor); } else { -- cgit v1.2.3