Android: Default to cortex-a8 CPU for ARMv7-A (#3439)

Hardcoded instead of pre-setting ldc2.conf for the prebuilt Android
packages, and thus simplifying cross-compilation (e.g., issue #3437).

Also use `core2` instead of `x86-64` for Android x86_64.

.azure-pipelines/posix.yml

@@ -137,7 +137,6 @@ steps:
     chmod 755 llvm-$ARCH/bin/llvm-config
     # Set up DFLAGS for cross-compiling/linking with host ldmd2
     DFLAGS="-mtriple=$LLVM_TRIPLE -L-L$PWD/ldc-build-runtime.tmp/lib -gcc=$PWD/android-ndk-r21/toolchains/llvm/prebuilt/linux-x86_64/bin/$ARCH-linux-${androidEnv}21-clang"
-    if [ "$ARCH" = "armv7a" ]; then DFLAGS="$DFLAGS -mcpu=cortex-a8"; fi
     set +x
     echo "##vso[task.setvariable variable=DFLAGS]$DFLAGS"
   displayName: 'Android: Set up cross-compilation'
@@ -159,8 +158,6 @@ steps:
     installDir=$PWD/install
     mkdir build-$ARCH
     cd build-$ARCH
-    DEFAULT_LDC_SWITCHES=''
-    if [ "$ARCH" = "armv7a" ]; then DEFAULT_LDC_SWITCHES=" \"-mcpu=cortex-a8\","; fi
     IFS=$'\n' extraFlags=( $(xargs -n1 <<<"$EXTRA_CMAKE_FLAGS $EXTRA_CMAKE_FLAGS_ANDROID") )
     cmake -G Ninja $BUILD_SOURCESDIRECTORY \
       -DCMAKE_BUILD_TYPE=Release \
@@ -169,7 +166,6 @@ steps:
       -DCMAKE_INSTALL_PREFIX=$installDir \
       -DINCLUDE_INSTALL_DIR=$installDir/import \
       -DD_LINKER_ARGS="-L$PWD/../ldc-build-runtime.tmp/lib;-lphobos2-ldc;-ldruntime-ldc" \
-      -DADDITIONAL_DEFAULT_LDC_SWITCHES="$DEFAULT_LDC_SWITCHES" \
       "${extraFlags[@]}"
     ninja -j$PARALLEL_JOBS -v ldc2 ldmd2 ldc-build-runtime ldc-profdata ldc-prune-cache
   displayName: 'Android: Cross-compile LDC executables'

driver/targetmachine.cpp

@@ -124,6 +124,13 @@ static std::string getX86TargetCPU(const llvm::Triple &triple) {
   if (triple.isOSDarwin()) {
     return triple.isArch64Bit() ? "core2" : "yonah";
   }
+
+  // All x86 devices running Android have core2 as their common
+  // denominator.
+  if (triple.getEnvironment() == llvm::Triple::Android) {
+    return "core2";
+  }
+
   // Everything else goes to x86-64 in 64-bit mode.
   if (triple.isArch64Bit()) {
     return "x86-64";
@@ -146,18 +153,20 @@ static std::string getX86TargetCPU(const llvm::Triple &triple) {
   if (triple.getOSName().startswith("dragonfly")) {
     return "i486";
   }
-  // All x86 devices running Android have core2 as their common
-  // denominator. This makes a better choice than pentium4.
-  if (triple.getEnvironment() == llvm::Triple::Android) {
-    return "core2";
 
-    // Fallback to p4.
-  }
+  // Fallback to p4.
   return "pentium4";
 }
 
 static std::string getARMTargetCPU(const llvm::Triple &triple) {
   auto defaultCPU = llvm::ARM::getDefaultCPU(triple.getArchName());
+
+  // 32-bit Android: default to cortex-a8
+  if (defaultCPU == "generic" &&
+      triple.getEnvironment() == llvm::Triple::Android) {
+    return "cortex-a8";
+  }
+
   if (!defaultCPU.empty())
     return std::string(defaultCPU);
 
@@ -291,8 +300,7 @@ const llvm::Target *lookupTarget(const std::string &arch, llvm::Triple &triple,
 
     if (!target) {
       errorMsg = "invalid target architecture '" + arch +
-                 "', see "
-                 "-version for a list of supported targets.";
+                 "', see -version for a list of supported targets.";
       return nullptr;
     }