[RISCV] Unify all the code that adds unaligned-scalar/vector-mem to Features vector. (#94660)

Instead of having multiple places insert into the Features vector
independently, check all the conditions in one place.

This avoids a subtle ordering requirement that -mstrict-align processing
had to be done after the others.

Author: topperc

clang/lib/Driver/ToolChains/Arch/RISCV.cpp

@@ -67,11 +67,6 @@ static void getRISCFeaturesFromMcpu(const Driver &D, const Arg *A,
       D.Diag(clang::diag::err_drv_unsupported_option_argument)
           << A->getSpelling() << Mcpu;
   }
-
-  if (llvm::RISCV::hasFastUnalignedAccess(Mcpu)) {
-    Features.push_back("+unaligned-scalar-mem");
-    Features.push_back("+unaligned-vector-mem");
-  }
 }
 
 void riscv::getRISCVTargetFeatures(const Driver &D, const llvm::Triple &Triple,
@@ -82,6 +77,8 @@ void riscv::getRISCVTargetFeatures(const Driver &D, const llvm::Triple &Triple,
   if (!getArchFeatures(D, MArch, Features, Args))
     return;
 
+  bool CPUFastUnaligned = false;
+
   // If users give march and mcpu, get std extension feature from MArch
   // and other features (ex. mirco architecture feature) from mcpu
   if (Arg *A = Args.getLastArg(options::OPT_mcpu_EQ)) {
@@ -90,6 +87,9 @@ void riscv::getRISCVTargetFeatures(const Driver &D, const llvm::Triple &Triple,
       CPU = llvm::sys::getHostCPUName();
 
     getRISCFeaturesFromMcpu(D, A, Triple, CPU, Features);
+
+    if (llvm::RISCV::hasFastUnalignedAccess(CPU))
+      CPUFastUnaligned = true;
   }
 
   // Handle features corresponding to "-ffixed-X" options
@@ -169,18 +169,23 @@ void riscv::getRISCVTargetFeatures(const Driver &D, const llvm::Triple &Triple,
     Features.push_back("-relax");
   }
 
-  // Android requires fast unaligned access on RISCV64.
-  if (Triple.isAndroid()) {
+  // If -mstrict-align or -mno-strict-align is passed, use it. Otherwise, the
+  // unaligned-*-mem is enabled if the CPU supports it or the target is
+  // Android.
+  if (const Arg *A = Args.getLastArg(options::OPT_mno_strict_align,
+                                     options::OPT_mstrict_align)) {
+    if (A->getOption().matches(options::OPT_mno_strict_align)) {
+      Features.push_back("+unaligned-scalar-mem");
+      Features.push_back("+unaligned-vector-mem");
+    } else {
+      Features.push_back("-unaligned-scalar-mem");
+      Features.push_back("-unaligned-vector-mem");
+    }
+  } else if (CPUFastUnaligned || Triple.isAndroid()) {
     Features.push_back("+unaligned-scalar-mem");
     Features.push_back("+unaligned-vector-mem");
   }
 
-  // -mstrict-align is default, unless -mno-strict-align is specified.
-  AddTargetFeature(Args, Features, options::OPT_mno_strict_align,
-                   options::OPT_mstrict_align, "unaligned-scalar-mem");
-  AddTargetFeature(Args, Features, options::OPT_mno_strict_align,
-                   options::OPT_mstrict_align, "unaligned-vector-mem");
-
   // Now add any that the user explicitly requested on the command line,
   // which may override the defaults.
   handleTargetFeaturesGroup(D, Triple, Args, Features,