[ARM] Add support for target("arm") and target("thumb").

[fhahn]

Summary

This patch adds support for the target("arm") and target("thumb")
attributes, which can be used to force the compiler to generated ARM or
Thumb code for a function.

In LLVM, ARM or Thumb code generation can be controlled by the
thumb-mode target feature. But GCC already uses target("arm") and
target("thumb"), so we have to substitute "arm" with -thumb-mode and
"thumb" with +thumb-mode.

[javed.absar]

include/clang/Basic/Attr.td

1774 ↗

(On Diff #100854)

Would this be a more accurate comment:

"...arm and thumb to thumb-mode" => "arm and thumb to arm-mode or thumb-mode, respectively"
Or
"[-|+] thumb-mode"

[fhahn]

reworded comment and improved test case to ensure only a single thumb-mode attribute is added.

[echristo]

include/clang/Basic/Attr.td

1790–1794 ↗

(On Diff #100880)

This is a little painful here - I wonder if we have access to TargetInfo or maybe translate it in the target specific area of the front end? I worry about this sort of thing getting unwieldy.

Thoughts?

Otherwise OK.

[fhahn]

Agreed, ARMTargetInfo is a much better place to do the conversion! Moved attribute conversion to ARMTargetInfo::initFeatureMap. Unfortunately FeaturesVec is const, so creating a mutable clone seemed the most straight-forward thing to do.

[echristo]

lib/Basic/Targets.cpp

5442–5445

Won't work below in handleTargetFeatures?

[fhahn]

lib/Basic/Targets.cpp

5442–5445

Unfortunately I don't think so, as it seems like handleTargetFeatures is only called once in TargetInfo::CreateTargetInfo (https://github.com/llvm-mirror/clang/blob/master/lib/Basic/Targets.cpp#L9679
), while initFeatureMap is called for each function and thus can be used to modify the user provided target-features for individual functions (
https://github.com/llvm-mirror/clang/blob/master/lib/CodeGen/CodeGenModule.cpp#L4426)

[ahatanak]

lib/Basic/Targets.cpp

5447

This can be "else if".

[fhahn]

use else if

[echristo]

Ah right. Thanks for looking.

LGTM.

-eric

lib/Basic/Targets.cpp

initFeatureMap(llvm::StringMap<bool> &Features, DiagnosticsEngine &Diags,
     // get default Extension features
     unsigned Extensions = llvm::ARM::getDefaultExtensions(CPU, Arch);
     llvm::ARM::getExtensionFeatures(Extensions, TargetFeatures);
 
     for (auto Feature : TargetFeatures)
       if (Feature[0] == '+')
         Features[Feature.drop_front(1)] = true;
 
-    return TargetInfo::initFeatureMap(Features, Diags, CPU, FeaturesVec);
+    // Convert user-provided arm and thumb GNU target attributes to
+    // [-|+]thumb-mode target features respectively.
+    std::vector<std::string> UpdatedFeaturesVec(FeaturesVec);
+    for (auto &Feature : UpdatedFeaturesVec) {
+      if (Feature.compare("+arm") == 0)
+        Feature = "-thumb-mode";
+      else if (Feature.compare("+thumb") == 0)
+        Feature = "+thumb-mode";
+    }
+
+    return TargetInfo::initFeatureMap(Features, Diags, CPU, UpdatedFeaturesVec);
   }
 
   bool handleTargetFeatures(std::vector<std::string> &Features,
                             DiagnosticsEngine &Diags) override {
     FPU = 0;
     CRC = 0;
     Crypto = 0;
     DSP = 0;

test/CodeGen/arm-target-attr.c

+// RUN: %clang_cc1 -triple thumb-apple-darwin -emit-llvm -o - %s | FileCheck --check-prefix CHECKPOS %s
+// RUN: %clang_cc1 -triple thumb-apple-darwin -emit-llvm -o - %s | FileCheck --check-prefix CHECKNEG %s
+// RUN: %clang_cc1 -triple arm-apple-darwin -emit-llvm -o - %s | FileCheck --check-prefix CHECKPOS %s
+// RUN: %clang_cc1 -triple arm-apple-darwin -emit-llvm -o - %s | FileCheck --check-prefix CHECKNEG %s
+
+__attribute__((target("arm"))) void test_target_arm() {
+  // CHECKPOS: define void @test_target_arm() [[ARM_ATTRS:#[0-9]+]]
+  // CHECKNEG: define void @test_target_arm() [[ARM_ATTRS:#[0-9]+]]
+}
+
+__attribute__((target("thumb"))) void test_target_thumb() {
+  // CHECKPOS: define void @test_target_thumb() [[THUMB_ATTRS:#[0-9]+]]
+  // CHECKNEG: define void @test_target_thumb() [[THUMB_ATTRS:#[0-9]+]]
+}
+
+// CHECKPOS: attributes [[ARM_ATTRS]] = { {{.*}} "target-features"="{{.*}}-thumb-mode{{.*}}"
+// CHECKPOS: attributes [[THUMB_ATTRS]] = { {{.*}} "target-features"="{{.*}}+thumb-mode{{.*}}"
+// CHECKNEG-NOT: attributes [[ARM_ATTRS]] = { {{.*}} "target-features"="{{.*}}+thumb-mode{{.*}}"
+// CHECKNEG-NOT: attributes [[THUMB_ATTRS]] = { {{.*}} "target-features"="{{.*}}-thumb-mode{{.*}}"