[Driver][CodeGen] Add -mprefer-vector-width driver option and attribute during CodeGen.

This adds a new command line option -mprefer-vector-width to specify a preferred vector width for the vectorizers. Valid values are 'none' and unsigned integers. The driver will check that it meets those constraints. Specific supported integers will be managed by the targets in the backend.

Clang will take the value and add it as a new function attribute during CodeGen.

This represents the alternate direction proposed by Sanjay in this RFC: http://lists.llvm.org/pipermail/llvm-dev/2017-November/118734.html

The syntax here matches gcc, though gcc treats it as an x86 specific command line argument. gcc only allows values of 128, 256, and 512. I'm not having clang check any values.

Differential Revision: https://reviews.llvm.org/D40230

llvm-svn: 320419

8 files changed, 79 insertions, 0 deletions

diff --git a/clang/docs/ClangCommandLineReference.rst b/clang/docs/ClangCommandLineReference.rst
index 9755efa2b8a..4d095883a4b 100644
--- a/clang/docs/ClangCommandLineReference.rst
+++ b/clang/docs/ClangCommandLineReference.rst
@@ -2120,6 +2120,10 @@ Omit frame pointer setup for leaf functions
 
 Use copy relocations support for PIE builds
 
+.. option:: -mprefer-vector-width=<arg>
+
+Specifies preferred vector width for auto-vectorization. Defaults to 'none' which allows target specific decisions.
+
 .. option:: -mqdsp6-compat
 
 Enable hexagon-qdsp6 backward compatibility
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index d155d703a79..1ed4fd2dab7 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -1954,6 +1954,8 @@ def mno_implicit_float : Flag<["-"], "mno-implicit-float">, Group<m_Group>,
 def mimplicit_float : Flag<["-"], "mimplicit-float">, Group<m_Group>;
 def mrecip : Flag<["-"], "mrecip">, Group<m_Group>;
 def mrecip_EQ : CommaJoined<["-"], "mrecip=">, Group<m_Group>, Flags<[CC1Option]>;
+def mprefer_vector_width_EQ : Joined<["-"], "mprefer-vector-width=">, Group<m_Group>, Flags<[CC1Option]>,
+  HelpText<"Specifies preferred vector width for auto-vectorization. Defaults to 'none' which allows target specific decisions.">;
 def mpie_copy_relocations : Flag<["-"], "mpie-copy-relocations">, Group<m_Group>,
   Flags<[CC1Option]>,
   HelpText<"Use copy relocations support for PIE builds">;
diff --git a/clang/include/clang/Frontend/CodeGenOptions.h b/clang/include/clang/Frontend/CodeGenOptions.h
index 425db0359e3..6b8d2b935fd 100644
--- a/clang/include/clang/Frontend/CodeGenOptions.h
+++ b/clang/include/clang/Frontend/CodeGenOptions.h
@@ -253,6 +253,11 @@ public:
 
   std::vector<std::string> Reciprocals;
 
+  /// The preferred width for auto-vectorization transforms. This is intended to
+  /// override default transforms based on the width of the architected vector
+  /// registers.
+  std::string PreferVectorWidth;
+
 public:
   // Define accessors/mutators for code generation options of enumeration type.
 #define CODEGENOPT(Name, Bits, Default)
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 15c8553249b..c3709bf2e44 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -1744,6 +1744,11 @@ void CodeGenModule::ConstructDefaultFnAttrList(StringRef Name, bool HasOptnone,
       FuncAttrs.addAttribute("reciprocal-estimates",
                              llvm::join(Recips, ","));
 
+    if (!CodeGenOpts.PreferVectorWidth.empty() &&
+        CodeGenOpts.PreferVectorWidth != "none")
+      FuncAttrs.addAttribute("prefer-vector-width",
+                             CodeGenOpts.PreferVectorWidth);
+
     if (CodeGenOpts.StackRealignment)
       FuncAttrs.addAttribute("stackrealign");
     if (CodeGenOpts.Backchain)
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 2d6ac642f0f..706ac5bee29 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -274,6 +274,27 @@ static void ParseMRecip(const Driver &D, const ArgList &Args,
   OutStrings.push_back(Args.MakeArgString(Out));
 }
 
+/// The -mprefer-vector-width option accepts either a positive integer
+/// or the string "none".
+static void ParseMPreferVectorWidth(const Driver &D, const ArgList &Args,
+                                    ArgStringList &CmdArgs) {
+  Arg *A = Args.getLastArg(options::OPT_mprefer_vector_width_EQ);
+  if (!A)
+    return;
+
+  StringRef Value = A->getValue();
+  if (Value == "none") {
+    CmdArgs.push_back("-mprefer-vector-width=none");
+  } else {
+    unsigned Width;
+    if (Value.getAsInteger(10, Width)) {
+      D.Diag(diag::err_drv_invalid_value) << A->getOption().getName() << Value;
+      return;
+    }
+    CmdArgs.push_back(Args.MakeArgString("-mprefer-vector-width=" + Value));
+  }
+}
+
 static void getWebAssemblyTargetFeatures(const ArgList &Args,
                                          std::vector<StringRef> &Features) {
   handleTargetFeaturesGroup(Args, Features, options::OPT_m_wasm_Features_Group);
@@ -4333,6 +4354,8 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
                    options::OPT_fno_slp_vectorize, EnableSLPVec))
     CmdArgs.push_back("-vectorize-slp");
 
+  ParseMPreferVectorWidth(D, Args, CmdArgs);
+
   if (Arg *A = Args.getLastArg(options::OPT_fshow_overloads_EQ))
     A->render(Args, CmdArgs);
 
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 2ebdc2a62aa..3aa615b490f 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -713,6 +713,8 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.VectorizeLoop = Args.hasArg(OPT_vectorize_loops);
   Opts.VectorizeSLP = Args.hasArg(OPT_vectorize_slp);
 
+  Opts.PreferVectorWidth = Args.getLastArgValue(OPT_mprefer_vector_width_EQ);
+
   Opts.MainFileName = Args.getLastArgValue(OPT_main_file_name);
   Opts.VerifyModule = !Args.hasArg(OPT_disable_llvm_verifier);
 
diff --git a/clang/test/CodeGen/attr-mprefer-vector-width.c b/clang/test/CodeGen/attr-mprefer-vector-width.c
new file mode 100644
index 00000000000..30edba5852f
--- /dev/null
+++ b/clang/test/CodeGen/attr-mprefer-vector-width.c
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -mprefer-vector-width=128 -emit-llvm %s -o - | FileCheck %s --check-prefix=CHECK128
+// RUN: %clang_cc1 -mprefer-vector-width=256 -emit-llvm %s -o - | FileCheck %s --check-prefix=CHECK256
+// RUN: %clang_cc1 -mprefer-vector-width=none -emit-llvm %s -o - | FileCheck %s --check-prefix=CHECKNONE
+
+int baz(int a) { return 4; }
+
+// CHECK128: baz{{.*}} #0
+// CHECK128: #0 = {{.*}}"prefer-vector-width"="128"
+
+// CHECK256: baz{{.*}} #0
+// CHECK256: #0 = {{.*}}"prefer-vector-width"="256"
+
+// CHECKNONE: baz{{.*}} #0
+// CHECKNONE-NOT: #0 = {{.*}}"prefer-vector-width"="none"
diff --git a/clang/test/Driver/mprefer-vector-width.c b/clang/test/Driver/mprefer-vector-width.c
new file mode 100644
index 00000000000..d927b35c098
--- /dev/null
+++ b/clang/test/Driver/mprefer-vector-width.c
@@ -0,0 +1,24 @@
+////
+//// Verify that valid options for the -mprefer-vector-width flag are passed through and invalid options cause an error.
+////
+
+//// If there are no options, convert to 'all'.
+
+// RUN: %clang -### -S %s -mprefer-vector-width=none  2>&1 | FileCheck --check-prefix=WIDTHNONE %s
+// WIDTHNONE: "-mprefer-vector-width=none"
+
+//// Check options that cover all types.
+
+// RUN: %clang -### -S %s -mprefer-vector-width=128  2>&1 | FileCheck --check-prefix=WIDTH128 %s
+// WIDTH128: "-mprefer-vector-width=128"
+
+//// Check invalid parameters.
+
+// RUN: %clang -### -S %s -mprefer-vector-width=one  2>&1 | FileCheck --check-prefix=WIDTHONE %s
+// WIDTHONE: invalid value 'one' in 'mprefer-vector-width='
+
+// RUN: %clang -### -S %s -mprefer-vector-width=128.5  2>&1 | FileCheck --check-prefix=WIDTH128p5 %s
+// WIDTH128p5: invalid value '128.5' in 'mprefer-vector-width='
+
+// RUN: %clang -### -S %s -mprefer-vector-width=-128  2>&1 | FileCheck --check-prefix=WIDTHNEG128 %s
+// WIDTHNEG128: invalid value '-128' in 'mprefer-vector-width='