Do not simultaneously clobber registers passed into assembly.

This is not actually legal (although the restriction is not
documented anywhere), and is not caught by LLVM unless the codegen
option -verify-machineinstrs is specified. This option is now used
on Travis.

While not legal, this does not seem to result in invalid output
(although it creates an unnecessary spill); however, under extremely
specific circumstances (e.g. when a register scavenger is run under
severe pressure), this will result in a codegen crash, which is
how I found it.

.travis.yml

@@ -3,8 +3,8 @@ rust: nightly
 sudo: false
 install:
   - .travis/docs/install
-script: 
-  - cargo build --verbose
+script:
+  - cargo rustc --verbose -- -C llvm-args=-verify-machineinstrs
   - cargo test --verbose
   - cargo bench --verbose
   - cargo doc

src/arch/or1k.rs

@@ -156,7 +156,7 @@ pub unsafe fn swap(arg: usize, old_sp: &mut StackPointer, new_sp: &StackPointer,
       "{r4}" (old_sp)
       "{r5}" (new_sp)
       "{r6}" (new_cfa)
-    :                      "r3",  "r4",  "r5",  "r6",  "r7",
+    :/*"r0", "r1",  "r2",  "r3",  "r4",  "r5",  "r6",*/"r7",
       "r8",  "r9",  "r10", "r11", "r12", "r13", "r14", "r15",
       "r16", "r17", "r18", "r19", "r20", "r21", "r22", "r23",
       "r24", "r25", "r26", "r27", "r28", "r29", "r30", "r31",

src/arch/x86.rs

@@ -151,7 +151,7 @@ pub unsafe fn swap(arg: usize, old_sp: &mut StackPointer, new_sp: &StackPointer,
       "{esi}" (old_sp)
       "{edx}" (new_sp)
       "{edi}" (new_cfa)
-    : "eax",  "ebx",  "ecx",  "edx",  "esi",  "edi", //"ebp",  "esp",
+    :/*"eax",*/"ebx",  "ecx",/*"edx",  "esi",  "edi", "ebp",  "esp",*/
       "mmx0", "mmx1", "mmx2", "mmx3", "mmx4", "mmx5", "mmx6", "mmx7",
       "xmm0", "xmm1", "xmm2", "xmm3", "xmm4", "xmm5", "xmm6", "xmm7",
       "cc", "fpsr", "flags", "memory"

src/arch/x86_64.rs

@@ -153,7 +153,7 @@ pub unsafe fn swap(arg: usize, old_sp: &mut StackPointer, new_sp: &StackPointer,
       "{rsi}" (old_sp)
       "{rdx}" (new_sp)
       "{rcx}" (new_cfa)
-    : "rax",   "rbx",   "rcx",   "rdx",   "rsi",   "rdi", //"rbp",   "rsp",
+    : "rax",   "rbx", /*"rcx",   "rdx",   "rsi",   "rdi",   "rbp",   "rsp",*/
       "r8",    "r9",    "r10",   "r11",   "r12",   "r13",   "r14",   "r15",
       "xmm0",  "xmm1",  "xmm2",  "xmm3",  "xmm4",  "xmm5",  "xmm6",  "xmm7",
       "xmm8",  "xmm9",  "xmm10", "xmm11", "xmm12", "xmm13", "xmm14", "xmm15",