[HLSL][SPIR-V] Add -fspv-enable-maximal-reconvergence flag to clang dxc.
#163474
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
llvmbot
added
clang
|
@llvm/pr-subscribers-hlsl @llvm/pr-subscribers-clang-codegen Author: Lucie Choi (luciechoi) ChangesImplement the frontend change to support maximal reconvergence feature. The next work is to generate the corresponding SPIR-V instructions ( Addresses #136930 Full diff: https://github.com/llvm/llvm-project/pull/163474.diff 5 Files Affected:
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index 9e850089ad87f..d32fecdb96f32 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -243,6 +243,7 @@ ENUM_LANGOPT(HLSLVersion, HLSLLangStd, 16, HLSL_Unset, NotCompatible, "HLSL Vers
LANGOPT(HLSLStrictAvailability, 1, 0, NotCompatible,
"Strict availability diagnostic mode for HLSL built-in functions.")
LANGOPT(HLSLSpvUseUnknownImageFormat, 1, 0, NotCompatible, "For storage images and texel buffers, sets the default format to 'Unknown' when not specified via the `vk::image_format` attribute. If this option is not used, the format is inferred from the resource's data type.")
+LANGOPT(HLSLSpvEnableMaximalReconvergence, 1, 0, NotCompatible, "Enables maximal reconvergence for SPIR-V codegen. This ensures that all control flow merges at the nearest possible merge point as defined by the Vulkan spec.")
LANGOPT(CUDAIsDevice , 1, 0, NotCompatible, "compiling for CUDA device")
LANGOPT(CUDAHostDeviceConstexpr, 1, 1, NotCompatible, "treating unattributed constexpr functions as __host__ __device__")
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 60c4ad408ee43..a6f7c6e12dddd 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -9573,6 +9573,15 @@ def fhlsl_spv_use_unknown_image_format
"from the resource's data type.">,
MarshallingInfoFlag<LangOpts<"HLSLSpvUseUnknownImageFormat">>;
+def fhlsl_spv_enable_maximal_reconvergence
+ : Flag<["-"], "fspv-enable-maximal-reconvergence">,
+ Group<dxc_Group>,
+ Visibility<[CC1Option, DXCOption]>,
+ HelpText<"Enables maximal reconvergence for SPIR-V codegen. This ensures "
+ "that all control flow merges at the nearest possible merge point "
+ "as defined by the Vulkan spec.">,
+ MarshallingInfoFlag<LangOpts<"HLSLSpvEnableMaximalReconvergence">>;
+
def no_wasm_opt : Flag<["--"], "no-wasm-opt">,
Group<m_Group>,
HelpText<"Disable the wasm-opt optimizer">,
diff --git a/clang/lib/CodeGen/CGHLSLRuntime.cpp b/clang/lib/CodeGen/CGHLSLRuntime.cpp
index ede1780592bf5..37c35a4768098 100644
--- a/clang/lib/CodeGen/CGHLSLRuntime.cpp
+++ b/clang/lib/CodeGen/CGHLSLRuntime.cpp
@@ -509,6 +509,10 @@ void clang::CodeGen::CGHLSLRuntime::setHLSLEntryAttributes(
if (CGM.getCodeGenOpts().OptimizationLevel == 0)
Fn->addFnAttr(llvm::Attribute::OptimizeNone);
Fn->addFnAttr(llvm::Attribute::NoInline);
+
+ if (CGM.getLangOpts().HLSLSpvEnableMaximalReconvergence) {
+ Fn->addFnAttr("enable-maximal-reconvergence", "true");
+ }
}
static Value *buildVectorInput(IRBuilder<> &B, Function *F, llvm::Type *Ty) {
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 107b9ffd439a3..1e794250d9d22 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -3755,7 +3755,8 @@ static void RenderHLSLOptions(const ArgList &Args, ArgStringList &CmdArgs,
options::OPT_hlsl_entrypoint,
options::OPT_fdx_rootsignature_define,
options::OPT_fdx_rootsignature_version,
- options::OPT_fhlsl_spv_use_unknown_image_format};
+ options::OPT_fhlsl_spv_use_unknown_image_format,
+ options::OPT_fhlsl_spv_enable_maximal_reconvergence};
if (!types::isHLSL(InputType))
return;
for (const auto &Arg : ForwardedArguments)
diff --git a/clang/test/CodeGenHLSL/vk-features/maximal_reconvergence.hlsl b/clang/test/CodeGenHLSL/vk-features/maximal_reconvergence.hlsl
new file mode 100644
index 0000000000000..870fbabaac1bf
--- /dev/null
+++ b/clang/test/CodeGenHLSL/vk-features/maximal_reconvergence.hlsl
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -triple spirv1.6-unknown-vulkan1.3-compute -fspv-enable-maximal-reconvergence -emit-llvm -o - -O0 %s | FileCheck %s --check-prefixes=CHECK
+// RUN: %clang_cc1 -triple spirv1.6-unknown-vulkan1.3-compute -hlsl-entry test -fspv-enable-maximal-reconvergence -emit-llvm -o - -O0 %s | FileCheck %s --check-prefixes=CHECK-ENTRY
+
+[numthreads(1,1,1)]
+void main() {
+// CHECK: define void @main() [[attributeNumber:#[0-9]+]] {
+}
+
+// CHECK: attributes [[attributeNumber]] = {{.*}} "enable-maximal-reconvergence"="true" {{.*}}
+
+
+[numthreads(1,1,1)]
+void test() {
+// CHECK-ENTRY: define void @test() [[attributeNumber:#[0-9]+]] {
+}
+
+// CHECK-ENTRY: attributes [[attributeNumber]] = {{.*}} "enable-maximal-reconvergence"="true" {{.*}}
\ No newline at end of file
|
|
@llvm/pr-subscribers-clang-driver Author: Lucie Choi (luciechoi) ChangesImplement the frontend change to support maximal reconvergence feature. The next work is to generate the corresponding SPIR-V instructions ( Addresses #136930 Full diff: https://github.com/llvm/llvm-project/pull/163474.diff 5 Files Affected:
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index 9e850089ad87f..d32fecdb96f32 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -243,6 +243,7 @@ ENUM_LANGOPT(HLSLVersion, HLSLLangStd, 16, HLSL_Unset, NotCompatible, "HLSL Vers
LANGOPT(HLSLStrictAvailability, 1, 0, NotCompatible,
"Strict availability diagnostic mode for HLSL built-in functions.")
LANGOPT(HLSLSpvUseUnknownImageFormat, 1, 0, NotCompatible, "For storage images and texel buffers, sets the default format to 'Unknown' when not specified via the `vk::image_format` attribute. If this option is not used, the format is inferred from the resource's data type.")
+LANGOPT(HLSLSpvEnableMaximalReconvergence, 1, 0, NotCompatible, "Enables maximal reconvergence for SPIR-V codegen. This ensures that all control flow merges at the nearest possible merge point as defined by the Vulkan spec.")
LANGOPT(CUDAIsDevice , 1, 0, NotCompatible, "compiling for CUDA device")
LANGOPT(CUDAHostDeviceConstexpr, 1, 1, NotCompatible, "treating unattributed constexpr functions as __host__ __device__")
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 60c4ad408ee43..a6f7c6e12dddd 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -9573,6 +9573,15 @@ def fhlsl_spv_use_unknown_image_format
"from the resource's data type.">,
MarshallingInfoFlag<LangOpts<"HLSLSpvUseUnknownImageFormat">>;
+def fhlsl_spv_enable_maximal_reconvergence
+ : Flag<["-"], "fspv-enable-maximal-reconvergence">,
+ Group<dxc_Group>,
+ Visibility<[CC1Option, DXCOption]>,
+ HelpText<"Enables maximal reconvergence for SPIR-V codegen. This ensures "
+ "that all control flow merges at the nearest possible merge point "
+ "as defined by the Vulkan spec.">,
+ MarshallingInfoFlag<LangOpts<"HLSLSpvEnableMaximalReconvergence">>;
+
def no_wasm_opt : Flag<["--"], "no-wasm-opt">,
Group<m_Group>,
HelpText<"Disable the wasm-opt optimizer">,
diff --git a/clang/lib/CodeGen/CGHLSLRuntime.cpp b/clang/lib/CodeGen/CGHLSLRuntime.cpp
index ede1780592bf5..37c35a4768098 100644
--- a/clang/lib/CodeGen/CGHLSLRuntime.cpp
+++ b/clang/lib/CodeGen/CGHLSLRuntime.cpp
@@ -509,6 +509,10 @@ void clang::CodeGen::CGHLSLRuntime::setHLSLEntryAttributes(
if (CGM.getCodeGenOpts().OptimizationLevel == 0)
Fn->addFnAttr(llvm::Attribute::OptimizeNone);
Fn->addFnAttr(llvm::Attribute::NoInline);
+
+ if (CGM.getLangOpts().HLSLSpvEnableMaximalReconvergence) {
+ Fn->addFnAttr("enable-maximal-reconvergence", "true");
+ }
}
static Value *buildVectorInput(IRBuilder<> &B, Function *F, llvm::Type *Ty) {
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 107b9ffd439a3..1e794250d9d22 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -3755,7 +3755,8 @@ static void RenderHLSLOptions(const ArgList &Args, ArgStringList &CmdArgs,
options::OPT_hlsl_entrypoint,
options::OPT_fdx_rootsignature_define,
options::OPT_fdx_rootsignature_version,
- options::OPT_fhlsl_spv_use_unknown_image_format};
+ options::OPT_fhlsl_spv_use_unknown_image_format,
+ options::OPT_fhlsl_spv_enable_maximal_reconvergence};
if (!types::isHLSL(InputType))
return;
for (const auto &Arg : ForwardedArguments)
diff --git a/clang/test/CodeGenHLSL/vk-features/maximal_reconvergence.hlsl b/clang/test/CodeGenHLSL/vk-features/maximal_reconvergence.hlsl
new file mode 100644
index 0000000000000..870fbabaac1bf
--- /dev/null
+++ b/clang/test/CodeGenHLSL/vk-features/maximal_reconvergence.hlsl
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -triple spirv1.6-unknown-vulkan1.3-compute -fspv-enable-maximal-reconvergence -emit-llvm -o - -O0 %s | FileCheck %s --check-prefixes=CHECK
+// RUN: %clang_cc1 -triple spirv1.6-unknown-vulkan1.3-compute -hlsl-entry test -fspv-enable-maximal-reconvergence -emit-llvm -o - -O0 %s | FileCheck %s --check-prefixes=CHECK-ENTRY
+
+[numthreads(1,1,1)]
+void main() {
+// CHECK: define void @main() [[attributeNumber:#[0-9]+]] {
+}
+
+// CHECK: attributes [[attributeNumber]] = {{.*}} "enable-maximal-reconvergence"="true" {{.*}}
+
+
+[numthreads(1,1,1)]
+void test() {
+// CHECK-ENTRY: define void @test() [[attributeNumber:#[0-9]+]] {
+}
+
+// CHECK-ENTRY: attributes [[attributeNumber]] = {{.*}} "enable-maximal-reconvergence"="true" {{.*}}
\ No newline at end of file
|
|
@llvm/pr-subscribers-clang Author: Lucie Choi (luciechoi) ChangesImplement the frontend change to support maximal reconvergence feature. The next work is to generate the corresponding SPIR-V instructions ( Addresses #136930 Full diff: https://github.com/llvm/llvm-project/pull/163474.diff 5 Files Affected:
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index 9e850089ad87f..d32fecdb96f32 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -243,6 +243,7 @@ ENUM_LANGOPT(HLSLVersion, HLSLLangStd, 16, HLSL_Unset, NotCompatible, "HLSL Vers
LANGOPT(HLSLStrictAvailability, 1, 0, NotCompatible,
"Strict availability diagnostic mode for HLSL built-in functions.")
LANGOPT(HLSLSpvUseUnknownImageFormat, 1, 0, NotCompatible, "For storage images and texel buffers, sets the default format to 'Unknown' when not specified via the `vk::image_format` attribute. If this option is not used, the format is inferred from the resource's data type.")
+LANGOPT(HLSLSpvEnableMaximalReconvergence, 1, 0, NotCompatible, "Enables maximal reconvergence for SPIR-V codegen. This ensures that all control flow merges at the nearest possible merge point as defined by the Vulkan spec.")
LANGOPT(CUDAIsDevice , 1, 0, NotCompatible, "compiling for CUDA device")
LANGOPT(CUDAHostDeviceConstexpr, 1, 1, NotCompatible, "treating unattributed constexpr functions as __host__ __device__")
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 60c4ad408ee43..a6f7c6e12dddd 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -9573,6 +9573,15 @@ def fhlsl_spv_use_unknown_image_format
"from the resource's data type.">,
MarshallingInfoFlag<LangOpts<"HLSLSpvUseUnknownImageFormat">>;
+def fhlsl_spv_enable_maximal_reconvergence
+ : Flag<["-"], "fspv-enable-maximal-reconvergence">,
+ Group<dxc_Group>,
+ Visibility<[CC1Option, DXCOption]>,
+ HelpText<"Enables maximal reconvergence for SPIR-V codegen. This ensures "
+ "that all control flow merges at the nearest possible merge point "
+ "as defined by the Vulkan spec.">,
+ MarshallingInfoFlag<LangOpts<"HLSLSpvEnableMaximalReconvergence">>;
+
def no_wasm_opt : Flag<["--"], "no-wasm-opt">,
Group<m_Group>,
HelpText<"Disable the wasm-opt optimizer">,
diff --git a/clang/lib/CodeGen/CGHLSLRuntime.cpp b/clang/lib/CodeGen/CGHLSLRuntime.cpp
index ede1780592bf5..37c35a4768098 100644
--- a/clang/lib/CodeGen/CGHLSLRuntime.cpp
+++ b/clang/lib/CodeGen/CGHLSLRuntime.cpp
@@ -509,6 +509,10 @@ void clang::CodeGen::CGHLSLRuntime::setHLSLEntryAttributes(
if (CGM.getCodeGenOpts().OptimizationLevel == 0)
Fn->addFnAttr(llvm::Attribute::OptimizeNone);
Fn->addFnAttr(llvm::Attribute::NoInline);
+
+ if (CGM.getLangOpts().HLSLSpvEnableMaximalReconvergence) {
+ Fn->addFnAttr("enable-maximal-reconvergence", "true");
+ }
}
static Value *buildVectorInput(IRBuilder<> &B, Function *F, llvm::Type *Ty) {
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 107b9ffd439a3..1e794250d9d22 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -3755,7 +3755,8 @@ static void RenderHLSLOptions(const ArgList &Args, ArgStringList &CmdArgs,
options::OPT_hlsl_entrypoint,
options::OPT_fdx_rootsignature_define,
options::OPT_fdx_rootsignature_version,
- options::OPT_fhlsl_spv_use_unknown_image_format};
+ options::OPT_fhlsl_spv_use_unknown_image_format,
+ options::OPT_fhlsl_spv_enable_maximal_reconvergence};
if (!types::isHLSL(InputType))
return;
for (const auto &Arg : ForwardedArguments)
diff --git a/clang/test/CodeGenHLSL/vk-features/maximal_reconvergence.hlsl b/clang/test/CodeGenHLSL/vk-features/maximal_reconvergence.hlsl
new file mode 100644
index 0000000000000..870fbabaac1bf
--- /dev/null
+++ b/clang/test/CodeGenHLSL/vk-features/maximal_reconvergence.hlsl
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -triple spirv1.6-unknown-vulkan1.3-compute -fspv-enable-maximal-reconvergence -emit-llvm -o - -O0 %s | FileCheck %s --check-prefixes=CHECK
+// RUN: %clang_cc1 -triple spirv1.6-unknown-vulkan1.3-compute -hlsl-entry test -fspv-enable-maximal-reconvergence -emit-llvm -o - -O0 %s | FileCheck %s --check-prefixes=CHECK-ENTRY
+
+[numthreads(1,1,1)]
+void main() {
+// CHECK: define void @main() [[attributeNumber:#[0-9]+]] {
+}
+
+// CHECK: attributes [[attributeNumber]] = {{.*}} "enable-maximal-reconvergence"="true" {{.*}}
+
+
+[numthreads(1,1,1)]
+void test() {
+// CHECK-ENTRY: define void @test() [[attributeNumber:#[0-9]+]] {
+}
+
+// CHECK-ENTRY: attributes [[attributeNumber]] = {{.*}} "enable-maximal-reconvergence"="true" {{.*}}
\ No newline at end of file
|
luciechoi
force-pushed
the
maximal_reconvergence
branch
from
269f4df to
fce0b6b
Compare
llvm-beanz
reviewed
Oct 15, 2025
I don't know how many drivers, particularly on Android, accept have the necessary extension. I'll have to double check, but I'm thinking we flip it when it is available in most places. EDIT: See https://vulkan.gpuinfo.org/displayextensiondetail.php?extension=VK_KHR_shader_maximal_reconvergence. Even on desktops, support is only around 25%. For android, support is at 5%. |
s-perron
reviewed
Oct 15, 2025
luciechoi
force-pushed
the
maximal_reconvergence
branch
from
2bd00d5 to
1997b10
Compare
s-perron
approved these changes
Oct 16, 2025
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
4 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Implement the frontend change to support maximal reconvergence feature.
The next work is to generate the corresponding SPIR-V instructions (
OpExtensionandOpExecutionMode) based on the llvm ir added in this CL"enable-maximal-reconvergence"="true".Addresses #136930