From 87666e5bce23c8ef420dfb0e5d86668ddf1acbf2 Mon Sep 17 00:00:00 2001
From: Lzu Tao <taolzu@gmail.com>
Date: Wed, 16 Sep 2020 04:46:23 +0000
Subject: [PATCH 1/2] Prefer asm! over llvm_asm! in core

---
 library/core/src/hint.rs                  |  5 +++--
 library/core/src/num/dec2flt/algorithm.rs | 20 +++++++++++++++++---
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/library/core/src/hint.rs b/library/core/src/hint.rs
index d40a380286762..929c22e4538f1 100644
--- a/library/core/src/hint.rs
+++ b/library/core/src/hint.rs
@@ -111,7 +111,7 @@ pub fn spin_loop() {
 #[inline]
 #[unstable(feature = "test", issue = "50297")]
 #[allow(unreachable_code)] // this makes #[cfg] a bit easier below.
-pub fn black_box<T>(dummy: T) -> T {
+pub fn black_box<T>(mut dummy: T) -> T {
     // We need to "use" the argument in some way LLVM can't introspect, and on
     // targets that support it we can typically leverage inline assembly to do
     // this. LLVM's interpretation of inline assembly is that it's, well, a black
@@ -121,7 +121,8 @@ pub fn black_box<T>(dummy: T) -> T {
     #[cfg(not(miri))] // This is just a hint, so it is fine to skip in Miri.
     // SAFETY: the inline assembly is a no-op.
     unsafe {
-        llvm_asm!("" : : "r"(&dummy));
+        // FIXME: Cannot use `asm!` because it doesn't support MIPS and other architectures.
+        llvm_asm!("" : : "r"(&mut dummy));
     }
 
     dummy
diff --git a/library/core/src/num/dec2flt/algorithm.rs b/library/core/src/num/dec2flt/algorithm.rs
index aaeb4d8a22c29..a5fbdc6ee2d48 100644
--- a/library/core/src/num/dec2flt/algorithm.rs
+++ b/library/core/src/num/dec2flt/algorithm.rs
@@ -60,12 +60,19 @@ mod fpu_precision {
     fn set_cw(cw: u16) {
         // SAFETY: the `fldcw` instruction has been audited to be able to work correctly with
         // any `u16`
-        unsafe { llvm_asm!("fldcw $0" :: "m" (cw) :: "volatile") }
+        unsafe {
+            asm!(
+                "fldcw ({})",
+                in(reg) &cw,
+                // FIXME: We are using ATT syntax to support LLVM 8 and LLVM 9.
+                options(att_syntax, nostack),
+            )
+        }
     }
 
     /// Sets the precision field of the FPU to `T` and returns a `FPUControlWord`.
     pub fn set_precision<T>() -> FPUControlWord {
-        let cw = 0u16;
+        let mut cw = 0_u16;
 
         // Compute the value for the Precision Control field that is appropriate for `T`.
         let cw_precision = match size_of::<T>() {
@@ -78,7 +85,14 @@ mod fpu_precision {
         // `FPUControlWord` structure is dropped
         // SAFETY: the `fnstcw` instruction has been audited to be able to work correctly with
         // any `u16`
-        unsafe { llvm_asm!("fnstcw $0" : "=*m" (&cw) ::: "volatile") }
+        unsafe {
+            asm!(
+                "fnstcw ({})",
+                in(reg) &mut cw,
+                // FIXME: We are using ATT syntax to support LLVM 8 and LLVM 9.
+                options(att_syntax, nostack),
+            )
+        }
 
         // Set the control word to the desired precision. This is achieved by masking away the old
         // precision (bits 8 and 9, 0x300) and replacing it with the precision flag computed above.

From 4dc4e9f671a36026cf59894622fdf4f6b979bf76 Mon Sep 17 00:00:00 2001
From: Lzu Tao <taolzu@gmail.com>
Date: Wed, 16 Sep 2020 09:25:54 +0000
Subject: [PATCH 2/2] Fix black_box bug detected by Amanieu

Co-authored-by: Amanieu <amanieu@gmail.com>
---
 library/core/src/hint.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/library/core/src/hint.rs b/library/core/src/hint.rs
index 929c22e4538f1..1192b9e164a14 100644
--- a/library/core/src/hint.rs
+++ b/library/core/src/hint.rs
@@ -122,7 +122,7 @@ pub fn black_box<T>(mut dummy: T) -> T {
     // SAFETY: the inline assembly is a no-op.
     unsafe {
         // FIXME: Cannot use `asm!` because it doesn't support MIPS and other architectures.
-        llvm_asm!("" : : "r"(&mut dummy));
+        llvm_asm!("" : : "r"(&mut dummy) : "memory" : "volatile");
     }
 
     dummy