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Document and update i686 triples #31632

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Document and update i686 triples #31632

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0062f72
Add comments about the differences between Clang and rustc target CPUs
ranma42 Feb 13, 2016
8c840ee
Synchronize i686 rustc triples with Clang
ranma42 Feb 13, 2016
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4 changes: 3 additions & 1 deletion src/librustc_back/target/i686_apple_darwin.rs
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Expand Up @@ -12,7 +12,9 @@ use target::Target;

pub fn target() -> Target {
let mut base = super::apple_base::opts();
base.cpu = "yonah".to_string();
// Use i686 as default CPU. Clang uses the same default.
base.cpu = "i686".to_string();
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According to the commit message that made this a yonah

Use more specific target CPUs on Darwin

Macs don't come with anything older than a Yonah (32bit) or Core2 (64bit), so we can default to those targets. Clang does the same.

I’m not sure why clang would change their default, but macs not existing with pre-yonah hardware seems like a pretty good reason to just use a yonah.

cc @dotdash

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See my comment above: Clang defaults to yonah on i386-apple-darwin, but not on i686-apple-darwin.

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@ranma42 but if there can’t possibly be such a combination of darwin+x86 which uses anything pre-yonah, why bother (EDIT: or, rather, restrict ourselves to) targeting a decade-older CPU?

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@ranma42 Hm, where does clang do that distinction? Did you check the code or is there a command I could use to reproduce/check this (without owning a Mac that is ;-))

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Nevermind, found the command in the other PR.

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So if I'm reading the code correctly, there's some special handling for Darwin that disables the automatic CPU selection for any x86 target except for the i386 one. I wonder whether that's actually intentional.

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@nagisa I do not know why Clang restricts itself to a decade-older CPU; we are about to do it in order to be consistent with Clang. I agree with you that it is surprising to have a sub-optimal default on Mac and that is the reason why I was suggesting to provide an i386-apple-darwin triple as default target for 32-bit Mac.

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Clang in this regard seems... somewhat inconsistent? At the very least it seems fine to leave this as-is and perhaps document the oddity (to allow this PR to land)


base.pre_link_args.push("-m32".to_string());

Target {
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6 changes: 5 additions & 1 deletion src/librustc_back/target/i686_linux_android.rs
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Expand Up @@ -12,7 +12,11 @@ use target::Target;

pub fn target() -> Target {
let mut base = super::android_base::opts();
base.cpu = "pentium4".to_string();

// Use i686 as default CPU and enable SSSE3.
// Clang and GCC do the same.
base.cpu = "i686".to_string();
base.features = "+ssse3".to_string();

Target {
llvm_target: "i686-linux-android".to_string(),
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3 changes: 3 additions & 0 deletions src/librustc_back/target/i686_pc_windows_gnu.rs
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Expand Up @@ -12,6 +12,9 @@ use target::Target;

pub fn target() -> Target {
let mut base = super::windows_base::opts();

// Use pentium4 as default CPU to enable SSE[2] instructions.
// Clang uses the same default.
base.cpu = "pentium4".to_string();

// Mark all dynamic libraries and executables as compatible with the larger 4GiB address
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3 changes: 3 additions & 0 deletions src/librustc_back/target/i686_pc_windows_msvc.rs
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Expand Up @@ -12,6 +12,9 @@ use target::Target;

pub fn target() -> Target {
let mut base = super::windows_msvc_base::opts();

// Use pentium4 as default CPU to enable SSE[2] instructions.
// Clang uses the same default.
base.cpu = "pentium4".to_string();

// Mark all dynamic libraries and executables as compatible with the larger 4GiB address
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4 changes: 4 additions & 0 deletions src/librustc_back/target/i686_unknown_dragonfly.rs
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Expand Up @@ -12,7 +12,11 @@ use target::Target;

pub fn target() -> Target {
let mut base = super::dragonfly_base::opts();

// Use pentium4 as default CPU to enable SSE[2] instructions.
// Clang uses the same default.
base.cpu = "pentium4".to_string();

base.pre_link_args.push("-m32".to_string());

Target {
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5 changes: 4 additions & 1 deletion src/librustc_back/target/i686_unknown_freebsd.rs
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Expand Up @@ -12,7 +12,10 @@ use target::Target;

pub fn target() -> Target {
let mut base = super::freebsd_base::opts();
base.cpu = "pentium4".to_string();

// Use i486 as default CPU. Clang uses the same default.
base.cpu = "i486".to_string();

base.pre_link_args.push("-m32".to_string());

Target {
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4 changes: 4 additions & 0 deletions src/librustc_back/target/i686_unknown_linux_gnu.rs
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Expand Up @@ -12,7 +12,11 @@ use target::Target;

pub fn target() -> Target {
let mut base = super::linux_base::opts();

// Use pentium4 as default CPU to enable SSE[2] instructions.
// Clang uses the same default.
base.cpu = "pentium4".to_string();

base.pre_link_args.push("-m32".to_string());

Target {
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4 changes: 4 additions & 0 deletions src/librustc_back/target/i686_unknown_linux_musl.rs
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Expand Up @@ -14,7 +14,11 @@ use target::Target;

pub fn target() -> Target {
let mut base = super::linux_base::opts();

// Use pentium4 as default CPU to enable SSE[2] instructions.
// Clang uses the same default.
base.cpu = "pentium4".to_string();

base.pre_link_args.push("-m32".to_string());
base.pre_link_args.push("-Wl,-melf_i386".to_string());

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