Rollup merge of #65151 - tmandry:revert-emscripten-upgrade, r=tmandry

Revert #63649 - "Upgrade Emscripten targets to use upstream LLVM backend"

This change caused the runtime of the linux-asmjs builder to nearly double from 2+ hours to about 4 hours, which happens to be the bors timeout. (It made it in barely under 4 hours when it was merged.) This is causing timeouts on all new changes.

This reverts commit 7870050796e5904a0fc85ecbe6fa6dde1cfe0c91, reversing
changes made to 2e7244807a7878f6eca3eb7d97ae9b413aa49014.

2 files changed, 54 insertions, 18 deletions

diff --git a/src/libcore/ffi.rs b/src/libcore/ffi.rs
index 0ea4187ccd4..eda0e7c518c 100644
--- a/src/libcore/ffi.rs
+++ b/src/libcore/ffi.rs
@@ -49,10 +49,8 @@ impl fmt::Debug for c_void {
 /// Basic implementation of a `va_list`.
 // The name is WIP, using `VaListImpl` for now.
 #[cfg(any(all(not(target_arch = "aarch64"), not(target_arch = "powerpc"),
-              not(target_arch = "x86_64")),
+              not(target_arch = "x86_64"), not(target_arch = "asmjs")),
           all(target_arch = "aarch64", target_os = "ios"),
-          target_arch = "wasm32",
-          target_arch = "asmjs",
           windows))]
 #[repr(transparent)]
 #[unstable(feature = "c_variadic",
@@ -69,10 +67,8 @@ pub struct VaListImpl<'f> {
 }
 
 #[cfg(any(all(not(target_arch = "aarch64"), not(target_arch = "powerpc"),
-              not(target_arch = "x86_64")),
+              not(target_arch = "x86_64"), not(target_arch = "asmjs")),
           all(target_arch = "aarch64", target_os = "ios"),
-          target_arch = "wasm32",
-          target_arch = "asmjs",
           windows))]
 #[unstable(feature = "c_variadic",
            reason = "the `c_variadic` feature has not been properly tested on \
@@ -141,6 +137,38 @@ pub struct VaListImpl<'f> {
     _marker: PhantomData<&'f mut &'f c_void>,
 }
 
+/// asm.js ABI implementation of a `va_list`.
+// asm.js uses the PNaCl ABI, which specifies that a `va_list` is
+// an array of 4 32-bit integers, according to the old PNaCl docs at
+// https://web.archive.org/web/20130518054430/https://www.chromium.org/nativeclient/pnacl/bitcode-abi#TOC-Derived-Types
+// and clang does the same in `CreatePNaClABIBuiltinVaListDecl` from `lib/AST/ASTContext.cpp`
+#[cfg(all(target_arch = "asmjs", not(windows)))]
+#[repr(C)]
+#[unstable(feature = "c_variadic",
+           reason = "the `c_variadic` feature has not been properly tested on \
+                     all supported platforms",
+           issue = "44930")]
+#[lang = "va_list"]
+pub struct VaListImpl<'f> {
+    inner: [crate::mem::MaybeUninit<i32>; 4],
+    _marker: PhantomData<&'f mut &'f c_void>,
+}
+
+#[cfg(all(target_arch = "asmjs", not(windows)))]
+#[unstable(feature = "c_variadic",
+           reason = "the `c_variadic` feature has not been properly tested on \
+                     all supported platforms",
+           issue = "44930")]
+impl<'f> fmt::Debug for VaListImpl<'f> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        unsafe {
+            write!(f, "va_list* [{:#x}, {:#x}, {:#x}, {:#x}]",
+                   self.inner[0].read(), self.inner[1].read(),
+                   self.inner[2].read(), self.inner[3].read())
+        }
+    }
+}
+
 /// A wrapper for a `va_list`
 #[repr(transparent)]
 #[derive(Debug)]
@@ -150,18 +178,14 @@ pub struct VaListImpl<'f> {
            issue = "44930")]
 pub struct VaList<'a, 'f: 'a> {
     #[cfg(any(all(not(target_arch = "aarch64"), not(target_arch = "powerpc"),
-                  not(target_arch = "x86_64")),
+                  not(target_arch = "x86_64"), not(target_arch = "asmjs")),
               all(target_arch = "aarch64", target_os = "ios"),
-              target_arch = "wasm32",
-              target_arch = "asmjs",
               windows))]
     inner: VaListImpl<'f>,
 
     #[cfg(all(any(target_arch = "aarch64", target_arch = "powerpc",
-                  target_arch = "x86_64"),
+                  target_arch = "x86_64", target_arch = "asmjs"),
               any(not(target_arch = "aarch64"), not(target_os = "ios")),
-              not(target_arch = "wasm32"),
-              not(target_arch = "asmjs"),
               not(windows)))]
     inner: &'a mut VaListImpl<'f>,
 
@@ -169,10 +193,8 @@ pub struct VaList<'a, 'f: 'a> {
 }
 
 #[cfg(any(all(not(target_arch = "aarch64"), not(target_arch = "powerpc"),
-              not(target_arch = "x86_64")),
+              not(target_arch = "x86_64"), not(target_arch = "asmjs")),
           all(target_arch = "aarch64", target_os = "ios"),
-          target_arch = "wasm32",
-          target_arch = "asmjs",
           windows))]
 #[unstable(feature = "c_variadic",
            reason = "the `c_variadic` feature has not been properly tested on \
@@ -190,10 +212,8 @@ impl<'f> VaListImpl<'f> {
 }
 
 #[cfg(all(any(target_arch = "aarch64", target_arch = "powerpc",
-              target_arch = "x86_64"),
+              target_arch = "x86_64", target_arch = "asmjs"),
           any(not(target_arch = "aarch64"), not(target_os = "ios")),
-          not(target_arch = "wasm32"),
-          not(target_arch = "asmjs"),
           not(windows)))]
 #[unstable(feature = "c_variadic",
            reason = "the `c_variadic` feature has not been properly tested on \
diff --git a/src/libcore/hint.rs b/src/libcore/hint.rs
index 368a2f16b28..ee4be6c9151 100644
--- a/src/libcore/hint.rs
+++ b/src/libcore/hint.rs
@@ -114,8 +114,24 @@ pub fn black_box<T>(dummy: T) -> T {
     // this. LLVM's intepretation of inline assembly is that it's, well, a black
     // box. This isn't the greatest implementation since it probably deoptimizes
     // more than we want, but it's so far good enough.
+    #[cfg(not(any(
+        target_arch = "asmjs",
+        all(
+            target_arch = "wasm32",
+            target_os = "emscripten"
+        )
+    )))]
     unsafe {
         asm!("" : : "r"(&dummy));
         return dummy;
     }
+
+    // Not all platforms support inline assembly so try to do something without
+    // inline assembly which in theory still hinders at least some optimizations
+    // on those targets. This is the "best effort" scenario.
+    unsafe {
+        let ret = crate::ptr::read_volatile(&dummy);
+        crate::mem::forget(dummy);
+        ret
+    }
 }