[OpenCL] Add '-cl-uniform-work-group-size' compile option

Summary:
OpenCL 2.0 specification defines '-cl-uniform-work-group-size' option,
which requires that the global work-size be a multiple of the work-group
size specified to clEnqueueNDRangeKernel and allows optimizations that
are made possible by this restriction.

The patch introduces the support of this option.

To keep information about whether an OpenCL kernel has uniform work
group size or not, clang generates 'uniform-work-group-size' function
attribute for every kernel:
- "uniform-work-group-size"="true" for OpenCL 1.2 and lower,
- "uniform-work-group-size"="true" for OpenCL 2.0 and higher if
 '-cl-uniform-work-group-size' option was specified,
- "uniform-work-group-size"="false" for OpenCL 2.0 and higher if no
 '-cl-uniform-work-group-size' options was specified.

If the function is not an OpenCL kernel, 'uniform-work-group-size'
attribute isn't generated.

Patch by: krisb

Reviewers: yaxunl, Anastasia, b-sumner

Reviewed By: yaxunl, Anastasia

Subscribers: nhaehnle, yaxunl, Anastasia, cfe-commits

Differential Revision: https://reviews.llvm.org/D43570

llvm-svn: 325771

3 files changed, 18 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index d62b080e31c..959df69f22e 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -1870,6 +1870,21 @@ void CodeGenModule::ConstructAttributeList(
     }
   }
 
+  if (TargetDecl && TargetDecl->hasAttr<OpenCLKernelAttr>()) {
+    if (getLangOpts().OpenCLVersion <= 120) {
+      // OpenCL v1.2 Work groups are always uniform
+      FuncAttrs.addAttribute("uniform-work-group-size", "true");
+    } else {
+      // OpenCL v2.0 Work groups may be whether uniform or not.
+      // '-cl-uniform-work-group-size' compile option gets a hint
+      // to the compiler that the global work-size be a multiple of
+      // the work-group size specified to clEnqueueNDRangeKernel
+      // (i.e. work groups are uniform).
+      FuncAttrs.addAttribute("uniform-work-group-size",
+                             llvm::toStringRef(CodeGenOpts.UniformWGSize));
+    }
+  }
+
   if (!AttrOnCallSite) {
     bool DisableTailCalls =
         CodeGenOpts.DisableTailCalls ||
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 64bea9e56ab..cc5cf0f042f 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2379,6 +2379,7 @@ static void RenderOpenCLOptions(const ArgList &Args, ArgStringList &CmdArgs) {
       options::OPT_cl_no_signed_zeros,
       options::OPT_cl_denorms_are_zero,
       options::OPT_cl_fp32_correctly_rounded_divide_sqrt,
+      options::OPT_cl_uniform_work_group_size
   };
 
   if (Arg *A = Args.getLastArg(options::OPT_cl_std_EQ)) {
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 3bdc116b963..5be02c96826 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -659,6 +659,8 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.FlushDenorm = Args.hasArg(OPT_cl_denorms_are_zero);
   Opts.CorrectlyRoundedDivSqrt =
       Args.hasArg(OPT_cl_fp32_correctly_rounded_divide_sqrt);
+  Opts.UniformWGSize =
+      Args.hasArg(OPT_cl_uniform_work_group_size);
   Opts.Reciprocals = Args.getAllArgValues(OPT_mrecip_EQ);
   Opts.ReciprocalMath = Args.hasArg(OPT_freciprocal_math);
   Opts.NoTrappingMath = Args.hasArg(OPT_fno_trapping_math);