[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

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

1775–1779

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

5439–5442 ↗

(On Diff #100994)

Won't work below in handleTargetFeatures?

[fhahn]

lib/Basic/Targets.cpp

5439–5442 ↗

(On Diff #100994)

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

5444 ↗

(On Diff #100994)

This can be "else if".

[fhahn]

use else if

[echristo]

Ah right. Thanks for looking.

LGTM.

-eric

include/clang/Basic/Attr.td

ParsedTargetAttr parse() const {
         // accepting it weirdly.
         Feature = Feature.trim();
 
         // We don't support cpu tuning this way currently.
         // TODO: Support the fpmath option. It will require checking
         // overall feature validity for the function with the rest of the
         // attributes on the function.
         if (Feature.startswith("fpmath=") || Feature.startswith("tune="))
-    continue;
+          continue;
 
+        // Convert GNU target names for arm and thumb to thumb-mode target
+        // feature.
+        if (Feature.compare("arm") == 0)
+          Ret.first.push_back("-thumb-mode");
+        else if (Feature.compare("thumb") == 0)
+          Ret.first.push_back("+thumb-mode");
         // While we're here iterating check for a different target cpu.
-        if (Feature.startswith("arch="))
+        else if (Feature.startswith("arch="))
           Ret.second = Feature.split("=").second.trim();
         else if (Feature.startswith("no-"))
           Ret.first.push_back("-" + Feature.split("-").second.str());
         else
           Ret.first.push_back("+" + Feature.str());
       }
       return Ret;
     }

test/CodeGen/arm-target-attr.c

+// RUN: %clang_cc1 -triple thumb-apple-darwin -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple arm-apple-darwin -emit-llvm -o - %s | FileCheck %s
+
+__attribute__((target("arm"))) void test_target_arm() {
+  // CHECK: define void @test_target_arm() [[ARM_ATTRS:#[0-9]+]]
+}
+
+__attribute__((target("thumb"))) void test_target_thumb() {
+  // CHECK: define void @test_target_thumb() [[THUMB_ATTRS:#[0-9]+]]
+}
+
+// CHECK: attributes [[ARM_ATTRS]] = { {{.*}} "target-features"="{{.*}}-thumb-mode{{.*}}"
+// CHECK: attributes [[THUMB_ATTRS]] = { {{.*}} "target-features"="{{.*}}+thumb-mode{{.*}}"