[clang] [llvm] [SPIR-V] Generate SPIR-V instructions when 'enable-maximal-reconvergence' function attribute is set (PR #163682)
Lucie Choi via cfe-commits
cfe-commits at lists.llvm.org
Thu Oct 16 11:30:26 PDT 2025
https://github.com/luciechoi updated https://github.com/llvm/llvm-project/pull/163682
>From 6c87062d610158fbd9080680f30ecba9f803f459 Mon Sep 17 00:00:00 2001
From: luciechoi <ychoi0407 at gmail.com>
Date: Wed, 15 Oct 2025 00:04:12 +0000
Subject: [PATCH 1/3] [SPIR-V] Generate SPIR-V instructions when
'enable-maximal-reconvergence' function attribute is set
[SPIR-V] Add maximal reconvergence instructions in SPIR-V codegen
---
clang/lib/Driver/ToolChains/HLSL.cpp | 38 ++++++++++++-------
llvm/docs/SPIRVUsage.rst | 2 +
llvm/lib/Target/SPIRV/SPIRVAsmPrinter.cpp | 20 ++++++++++
llvm/lib/Target/SPIRV/SPIRVCommandLine.cpp | 4 +-
llvm/lib/Target/SPIRV/SPIRVModuleAnalysis.cpp | 3 ++
.../lib/Target/SPIRV/SPIRVSymbolicOperands.td | 4 +-
.../enable-maximal-reconvergence.ll | 12 ++++++
7 files changed, 68 insertions(+), 15 deletions(-)
create mode 100644 llvm/test/CodeGen/SPIRV/extensions/SPV_KHR_maximal_reconvergence/enable-maximal-reconvergence.ll
diff --git a/clang/lib/Driver/ToolChains/HLSL.cpp b/clang/lib/Driver/ToolChains/HLSL.cpp
index 5c8891fbfb98a..20a320ea233d4 100644
--- a/clang/lib/Driver/ToolChains/HLSL.cpp
+++ b/clang/lib/Driver/ToolChains/HLSL.cpp
@@ -191,23 +191,35 @@ void getSpirvExtOperand(StringRef SpvExtensionArg, raw_ostream &out) {
// The extensions that are commented out are supported in DXC, but the SPIR-V
// backend does not know about them yet.
static const std::vector<StringRef> DxcSupportedExtensions = {
- "SPV_KHR_16bit_storage", "SPV_KHR_device_group",
- "SPV_KHR_fragment_shading_rate", "SPV_KHR_multiview",
- "SPV_KHR_post_depth_coverage", "SPV_KHR_non_semantic_info",
- "SPV_KHR_shader_draw_parameters", "SPV_KHR_ray_tracing",
- "SPV_KHR_shader_clock", "SPV_EXT_demote_to_helper_invocation",
- "SPV_EXT_descriptor_indexing", "SPV_EXT_fragment_fully_covered",
+ "SPV_KHR_16bit_storage",
+ "SPV_KHR_device_group",
+ "SPV_KHR_fragment_shading_rate",
+ "SPV_KHR_multiview",
+ "SPV_KHR_post_depth_coverage",
+ "SPV_KHR_non_semantic_info",
+ "SPV_KHR_shader_draw_parameters",
+ "SPV_KHR_ray_tracing",
+ "SPV_KHR_shader_clock",
+ "SPV_EXT_demote_to_helper_invocation",
+ "SPV_EXT_descriptor_indexing",
+ "SPV_EXT_fragment_fully_covered",
"SPV_EXT_fragment_invocation_density",
- "SPV_EXT_fragment_shader_interlock", "SPV_EXT_mesh_shader",
- "SPV_EXT_shader_stencil_export", "SPV_EXT_shader_viewport_index_layer",
+ "SPV_EXT_fragment_shader_interlock",
+ "SPV_EXT_mesh_shader",
+ "SPV_EXT_shader_stencil_export",
+ "SPV_EXT_shader_viewport_index_layer",
// "SPV_AMD_shader_early_and_late_fragment_tests",
- "SPV_GOOGLE_hlsl_functionality1", "SPV_GOOGLE_user_type",
- "SPV_KHR_ray_query", "SPV_EXT_shader_image_int64",
- "SPV_KHR_fragment_shader_barycentric", "SPV_KHR_physical_storage_buffer",
+ "SPV_GOOGLE_hlsl_functionality1",
+ "SPV_GOOGLE_user_type",
+ "SPV_KHR_ray_query",
+ "SPV_EXT_shader_image_int64",
+ "SPV_KHR_fragment_shader_barycentric",
+ "SPV_KHR_physical_storage_buffer",
"SPV_KHR_vulkan_memory_model",
// "SPV_KHR_compute_shader_derivatives",
- // "SPV_KHR_maximal_reconvergence",
- "SPV_KHR_float_controls", "SPV_NV_shader_subgroup_partitioned",
+ "SPV_KHR_maximal_reconvergence",
+ "SPV_KHR_float_controls",
+ "SPV_NV_shader_subgroup_partitioned",
// "SPV_KHR_quad_control"
};
diff --git a/llvm/docs/SPIRVUsage.rst b/llvm/docs/SPIRVUsage.rst
index d2d66462b5df9..85eeabf10244a 100644
--- a/llvm/docs/SPIRVUsage.rst
+++ b/llvm/docs/SPIRVUsage.rst
@@ -235,6 +235,8 @@ Below is a list of supported SPIR-V extensions, sorted alphabetically by their e
- Adds execution modes and decorations to control floating-point computations in both kernels and shaders. It can be used on whole modules and individual instructions.
* - ``SPV_INTEL_predicated_io``
- Adds predicated load and store instructions that conditionally read from or write to memory based on a boolean predicate.
+ * - ``SPV_KHR_maximal_reconvergence``
+ - Adds execution mode and capability to enable maximal reconvergence.
SPIR-V representation in LLVM IR
================================
diff --git a/llvm/lib/Target/SPIRV/SPIRVAsmPrinter.cpp b/llvm/lib/Target/SPIRV/SPIRVAsmPrinter.cpp
index 56a6168775365..640b014646f36 100644
--- a/llvm/lib/Target/SPIRV/SPIRVAsmPrinter.cpp
+++ b/llvm/lib/Target/SPIRV/SPIRVAsmPrinter.cpp
@@ -78,6 +78,8 @@ class SPIRVAsmPrinter : public AsmPrinter {
void outputExecutionModeFromNumthreadsAttribute(
const MCRegister &Reg, const Attribute &Attr,
SPIRV::ExecutionMode::ExecutionMode EM);
+ void outputExecutionModeFromEnableMaximalReconvergenceAttr(
+ const MCRegister &Reg, const SPIRVSubtarget &ST);
void outputExecutionMode(const Module &M);
void outputAnnotations(const Module &M);
void outputModuleSections();
@@ -495,6 +497,20 @@ void SPIRVAsmPrinter::outputExecutionModeFromNumthreadsAttribute(
outputMCInst(Inst);
}
+void SPIRVAsmPrinter::outputExecutionModeFromEnableMaximalReconvergenceAttr(
+ const MCRegister &Reg, const SPIRVSubtarget &ST) {
+ assert(ST.canUseExtension(SPIRV::Extension::SPV_KHR_maximal_reconvergence) &&
+ "Function called when SPV_KHR_maximal_reconvergence is not enabled.");
+
+ MCInst Inst;
+ Inst.setOpcode(SPIRV::OpExecutionMode);
+ Inst.addOperand(MCOperand::createReg(Reg));
+ unsigned EM =
+ static_cast<unsigned>(SPIRV::ExecutionMode::MaximallyReconvergesKHR);
+ Inst.addOperand(MCOperand::createImm(EM));
+ outputMCInst(Inst);
+}
+
void SPIRVAsmPrinter::outputExecutionMode(const Module &M) {
NamedMDNode *Node = M.getNamedMetadata("spirv.ExecutionMode");
if (Node) {
@@ -551,6 +567,10 @@ void SPIRVAsmPrinter::outputExecutionMode(const Module &M) {
if (Attribute Attr = F.getFnAttribute("hlsl.numthreads"); Attr.isValid())
outputExecutionModeFromNumthreadsAttribute(
FReg, Attr, SPIRV::ExecutionMode::LocalSize);
+ if (Attribute Attr = F.getFnAttribute("enable-maximal-reconvergence");
+ Attr.getValueAsBool()) {
+ outputExecutionModeFromEnableMaximalReconvergenceAttr(FReg, *ST);
+ }
if (MDNode *Node = F.getMetadata("work_group_size_hint"))
outputExecutionModeFromMDNode(FReg, Node,
SPIRV::ExecutionMode::LocalSizeHint, 3, 1);
diff --git a/llvm/lib/Target/SPIRV/SPIRVCommandLine.cpp b/llvm/lib/Target/SPIRV/SPIRVCommandLine.cpp
index 5f3ed862af893..96f5dee21bc2a 100644
--- a/llvm/lib/Target/SPIRV/SPIRVCommandLine.cpp
+++ b/llvm/lib/Target/SPIRV/SPIRVCommandLine.cpp
@@ -153,7 +153,9 @@ static const std::map<std::string, SPIRV::Extension::Extension, std::less<>>
SPIRV::Extension::Extension::
SPV_EXT_relaxed_printf_string_address_space},
{"SPV_INTEL_predicated_io",
- SPIRV::Extension::Extension::SPV_INTEL_predicated_io}};
+ SPIRV::Extension::Extension::SPV_INTEL_predicated_io},
+ {"SPV_KHR_maximal_reconvergence",
+ SPIRV::Extension::Extension::SPV_KHR_maximal_reconvergence}};
bool SPIRVExtensionsParser::parse(cl::Option &O, StringRef ArgName,
StringRef ArgValue,
diff --git a/llvm/lib/Target/SPIRV/SPIRVModuleAnalysis.cpp b/llvm/lib/Target/SPIRV/SPIRVModuleAnalysis.cpp
index 5144fb14fa6a6..6760f5a2829d3 100644
--- a/llvm/lib/Target/SPIRV/SPIRVModuleAnalysis.cpp
+++ b/llvm/lib/Target/SPIRV/SPIRVModuleAnalysis.cpp
@@ -2155,6 +2155,9 @@ static void collectReqs(const Module &M, SPIRV::ModuleAnalysisInfo &MAI,
SPIRV::OperandCategory::ExecutionModeOperand,
SPIRV::ExecutionMode::LocalSize, ST);
}
+ if (F.getFnAttribute("enable-maximal-reconvergence").getValueAsBool()) {
+ MAI.Reqs.addExtension(SPIRV::Extension::SPV_KHR_maximal_reconvergence);
+ }
if (F.getMetadata("work_group_size_hint"))
MAI.Reqs.getAndAddRequirements(
SPIRV::OperandCategory::ExecutionModeOperand,
diff --git a/llvm/lib/Target/SPIRV/SPIRVSymbolicOperands.td b/llvm/lib/Target/SPIRV/SPIRVSymbolicOperands.td
index 26256429537e9..7d08b29a51a6e 100644
--- a/llvm/lib/Target/SPIRV/SPIRVSymbolicOperands.td
+++ b/llvm/lib/Target/SPIRV/SPIRVSymbolicOperands.td
@@ -386,6 +386,7 @@ defm SPV_KHR_float_controls2 : ExtensionOperand<124, [EnvVulkan, EnvOpenCL]>;
defm SPV_INTEL_tensor_float32_conversion : ExtensionOperand<125, [EnvOpenCL]>;
defm SPV_KHR_bfloat16 : ExtensionOperand<126, [EnvVulkan, EnvOpenCL]>;
defm SPV_INTEL_predicated_io : ExtensionOperand<127, [EnvOpenCL]>;
+defm SPV_KHR_maximal_reconvergence : ExtensionOperand<128, [EnvVulkan]>;
//===----------------------------------------------------------------------===//
// Multiclass used to define Capabilities enum values and at the same time
@@ -698,7 +699,7 @@ defm IntersectionNV: ExecutionModelOperand<5314, [RayTracingNV]>;
defm AnyHitNV: ExecutionModelOperand<5315, [RayTracingNV]>;
defm ClosestHitNV: ExecutionModelOperand<5316, [RayTracingNV]>;
defm MissNV: ExecutionModelOperand<5317, [RayTracingNV]>;
-defm CallableNV: ExecutionModelOperand<5318, [RayTracingNV]>;
+defm CallableNV : ExecutionModelOperand<5318, [RayTracingNV]>;
//===----------------------------------------------------------------------===//
// Multiclass used to define MemoryModel enum values and at the same time
@@ -805,6 +806,7 @@ defm RoundingModeRTNINTEL : ExecutionModeOperand<5621, [RoundToInfinityINTEL]>;
defm FloatingPointModeALTINTEL : ExecutionModeOperand<5622, [FloatingPointModeINTEL]>;
defm FloatingPointModeIEEEINTEL : ExecutionModeOperand<5623, [FloatingPointModeINTEL]>;
defm FPFastMathDefault : ExecutionModeOperand<6028, [FloatControls2]>;
+defm MaximallyReconvergesKHR : ExecutionModeOperand<6023, [Shader]>;
//===----------------------------------------------------------------------===//
// Multiclass used to define StorageClass enum values and at the same time
diff --git a/llvm/test/CodeGen/SPIRV/extensions/SPV_KHR_maximal_reconvergence/enable-maximal-reconvergence.ll b/llvm/test/CodeGen/SPIRV/extensions/SPV_KHR_maximal_reconvergence/enable-maximal-reconvergence.ll
new file mode 100644
index 0000000000000..662190e039957
--- /dev/null
+++ b/llvm/test/CodeGen/SPIRV/extensions/SPV_KHR_maximal_reconvergence/enable-maximal-reconvergence.ll
@@ -0,0 +1,12 @@
+; RUN: llc -O0 -verify-machineinstrs -mtriple=spirv1.6-unknown-vulkan1.3-compute --spirv-ext=+SPV_KHR_maximal_reconvergence %s -o - | FileCheck %s
+; RUN: %if spirv-tools %{ llc -O0 -mtriple=spirv1.6-unknown-vulkan1.3-compute --spirv-ext=+SPV_KHR_maximal_reconvergence %s -o - -filetype=obj | spirv-val %}
+
+; CHECK: OpCapability Shader
+; CHECK: OpExtension "SPV_KHR_maximal_reconvergence"
+; CHECK: OpExecutionMode {{.*}} MaximallyReconvergesKHR
+define void @main() local_unnamed_addr #0 {
+entry:
+ ret void
+}
+
+attributes #0 = { mustprogress nofree noinline norecurse nosync nounwind willreturn memory(none) "enable-maximal-reconvergence"="true" "frame-pointer"="all" "hlsl.numthreads"="1,1,1" "hlsl.shader"="compute" "no-infs-fp-math"="true" "no-nans-fp-math"="true" "no-signed-zeros-fp-math"="true" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
>From 2cb4613ce05fd67bba660c6d9958702e6239fe87 Mon Sep 17 00:00:00 2001
From: luciechoi <ychoi0407 at gmail.com>
Date: Thu, 16 Oct 2025 17:41:24 +0000
Subject: [PATCH 2/3] Add a negative test case
---
.../enable-maximal-reconvergence.ll | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/llvm/test/CodeGen/SPIRV/extensions/SPV_KHR_maximal_reconvergence/enable-maximal-reconvergence.ll b/llvm/test/CodeGen/SPIRV/extensions/SPV_KHR_maximal_reconvergence/enable-maximal-reconvergence.ll
index 662190e039957..b4f95cf01b26f 100644
--- a/llvm/test/CodeGen/SPIRV/extensions/SPV_KHR_maximal_reconvergence/enable-maximal-reconvergence.ll
+++ b/llvm/test/CodeGen/SPIRV/extensions/SPV_KHR_maximal_reconvergence/enable-maximal-reconvergence.ll
@@ -3,10 +3,18 @@
; CHECK: OpCapability Shader
; CHECK: OpExtension "SPV_KHR_maximal_reconvergence"
+; CHECK-NOT: OpExtension "SPV_KHR_maximal_reconvergence"
; CHECK: OpExecutionMode {{.*}} MaximallyReconvergesKHR
+; CHECK-NOT: OpExecutionMode {{.*}} MaximallyReconvergesKHR
define void @main() local_unnamed_addr #0 {
entry:
ret void
}
-attributes #0 = { mustprogress nofree noinline norecurse nosync nounwind willreturn memory(none) "enable-maximal-reconvergence"="true" "frame-pointer"="all" "hlsl.numthreads"="1,1,1" "hlsl.shader"="compute" "no-infs-fp-math"="true" "no-nans-fp-math"="true" "no-signed-zeros-fp-math"="true" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
+define void @negative() local_unnamed_addr #1 {
+entry:
+ ret void
+}
+
+attributes #0 = { "enable-maximal-reconvergence"="true" "hlsl.numthreads"="1,1,1" "hlsl.shader"="compute" }
+attributes #1 = { "hlsl.numthreads"="1,1,1" "hlsl.shader"="compute" }
>From e0f30f19aba57c19fea46ddd9290283d035381b2 Mon Sep 17 00:00:00 2001
From: luciechoi <ychoi0407 at gmail.com>
Date: Thu, 16 Oct 2025 18:24:50 +0000
Subject: [PATCH 3/3] Fix tests
---
.../enable-maximal-reconvergence.ll | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/llvm/test/CodeGen/SPIRV/extensions/SPV_KHR_maximal_reconvergence/enable-maximal-reconvergence.ll b/llvm/test/CodeGen/SPIRV/extensions/SPV_KHR_maximal_reconvergence/enable-maximal-reconvergence.ll
index b4f95cf01b26f..456aad2ca5533 100644
--- a/llvm/test/CodeGen/SPIRV/extensions/SPV_KHR_maximal_reconvergence/enable-maximal-reconvergence.ll
+++ b/llvm/test/CodeGen/SPIRV/extensions/SPV_KHR_maximal_reconvergence/enable-maximal-reconvergence.ll
@@ -3,9 +3,9 @@
; CHECK: OpCapability Shader
; CHECK: OpExtension "SPV_KHR_maximal_reconvergence"
-; CHECK-NOT: OpExtension "SPV_KHR_maximal_reconvergence"
-; CHECK: OpExecutionMode {{.*}} MaximallyReconvergesKHR
+; CHECK: OpExecutionMode [[main:%[0-9]+]] MaximallyReconvergesKHR
; CHECK-NOT: OpExecutionMode {{.*}} MaximallyReconvergesKHR
+; CHECK: OpName [[main]] "main"
define void @main() local_unnamed_addr #0 {
entry:
ret void
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