clang driver: enable fast unaligned access for Android on RISCV64

[hiraditya]

Android CTS test already requires fast unaligned access https://android-review.googlesource.com/c/platform/cts/+/2675633

[llvmbot]

@llvm/pr-subscribers-clang-driver
@llvm/pr-subscribers-backend-risc-v

@llvm/pr-subscribers-clang

Author: AdityaK (hiraditya)

Changes

Android CTS test already requires fast unaligned access https://android-review.googlesource.com/c/platform/cts/+/2675633

Pending testcase

---

Full diff: https://github.com/llvm/llvm-project/pull/85704.diff

2 Files Affected:

• (modified) clang/lib/Driver/ToolChains/Arch/RISCV.cpp (+4)
• (modified) clang/test/Driver/riscv-features.c (+1-1)

diff --git a/clang/lib/Driver/ToolChains/Arch/RISCV.cpp b/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
index 5165bccc6d7e30..b1dd7c4372d475 100644
--- a/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
+++ b/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
@@ -167,6 +167,10 @@ void riscv::getRISCVTargetFeatures(const Driver &D, const llvm::Triple &Triple,
     Features.push_back("-relax");
   }
 
+  // Android requires fast unaligned access on RISCV64.
+  if (Triple.isAndroid())
+    Features.push_back("+fast-unaligned-access");
+
   // -mstrict-align is default, unless -mno-strict-align is specified.
   AddTargetFeature(Args, Features, options::OPT_mno_strict_align,
                    options::OPT_mstrict_align, "fast-unaligned-access");
diff --git a/clang/test/Driver/riscv-features.c b/clang/test/Driver/riscv-features.c
index fe74ac773ef8ca..7db3adb117ae47 100644
--- a/clang/test/Driver/riscv-features.c
+++ b/clang/test/Driver/riscv-features.c
@@ -1,7 +1,7 @@
 // RUN: %clang --target=riscv32-unknown-elf -### %s -fsyntax-only 2>&1 | FileCheck %s
 // RUN: %clang --target=riscv64-unknown-elf -### %s -fsyntax-only 2>&1 | FileCheck %s
 // RUN: %clang --target=riscv64-linux-android -### %s -fsyntax-only 2>&1 | FileCheck %s -check-prefixes=ANDROID,DEFAULT
-// RUN: %clang -mabi=lp64d --target=riscv64-linux-android -### %s -fsyntax-only 2>&1 | FileCheck %s -check-prefixes=ANDROID,DEFAULT
+// RUN: %clang -mabi=lp64d --target=riscv64-linux-android -### %s -fsyntax-only 2>&1 | FileCheck %s -check-prefixes=ANDROID,DEFAULT,FAST-UNALIGNED-ACCESS
 
 // CHECK: fno-signed-char
 

[enh-google]

thanks!

[MaskRay]

This adds two +fast-unaligned-access if -mno-strict-align is specified. Best to update the following AddTargetFeature in case -mstrict-align is specified.

[hiraditya]

./bin/clang -mabi=lp64d --target=riscv64-linux-android -### -fsyntax-only ../clang/test/Driver/riscv-features.c -mno-strict-align

prints only one "-target-feature" "+fast-unaligned-access"

[hiraditya]

AIUI, it seems common to add target-features as requested and then at the end tools::unifyTargetFeatures normalizes the flags.

[pirama-arumuga-nainar]

I think the concern is that -target riscv64-linux-android -mstrict-align will add +fast-unaligned-access and -fast-unaligned-access - which would not be handled correctly by unifyTargetFeatures.

[hiraditya]

Added a test to check that following -mstrict-align would disable fast unaligned access.

[MaskRay]

.