Compile tools and internal libraries with the initial-exec TLS model

joshtriplett · Mark-Simulacrum · joshtriplett · commit 0328e69287b0 · 2020-11-06T15:07:05.000-08:00
This should produce more efficient code, with fewer calls to
__tls_get_addr. The tradeoff is that libraries using it won't work with
dlopen, but that shouldn't be a problem for tools or for our own
internal libraries.

Co-authored-by: Mark Rousskov &lt;mark.simulacrum@gmail.com&gt;
diff --git a/src/bootstrap/builder.rs b/src/bootstrap/builder.rs
@@ -1140,6 +1140,14 @@ impl<'a> Builder<'a> {
             }
         }
 
+        // Compile everything except libraries and proc macros with the more
+        // efficient initial-exec TLS model. This doesn't work with `dlopen`,
+        // so we can't use it by default in general, but we can use it for tools
+        // and our own internal libraries.
+        if !mode.must_support_dlopen() {
+            rustflags.arg("-Ztls-model=initial-exec");
+        }
+
         if self.config.incremental {
             cargo.env("CARGO_INCREMENTAL", "1");
         } else {
diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
@@ -332,6 +332,10 @@ impl Mode {
     pub fn is_tool(&self) -> bool {
         matches!(self, Mode::ToolBootstrap | Mode::ToolRustc | Mode::ToolStd)
     }
+
+    pub fn must_support_dlopen(&self) -> bool {
+        matches!(self, Mode::Std | Mode::Codegen)
+    }
 }
 
 impl Build {

Original file line number	Diff line number	Diff line change
`@@ -1140,6 +1140,14 @@ impl<'a> Builder<'a> {`
`1140`	`1140`	`}`
`1141`	`1141`	`}`
`1142`	`1142`
	`1143`	`+ // Compile everything except libraries and proc macros with the more`
	`1144`	+ // efficient initial-exec TLS model. This doesn't work with `dlopen`,
	`1145`	`+ // so we can't use it by default in general, but we can use it for tools`
	`1146`	`+ // and our own internal libraries.`
	`1147`	`+ if !mode.must_support_dlopen() {`
	`1148`	`+ rustflags.arg("-Ztls-model=initial-exec");`
	`1149`	`+ }`
	`1150`	`+`
`1143`	`1151`	`if self.config.incremental {`
`1144`	`1152`	`cargo.env("CARGO_INCREMENTAL", "1");`
`1145`	`1153`	`} else {`
Original file line number	Diff line number	Diff line change
`@@ -332,6 +332,10 @@ impl Mode {`
`332`	`332`	`pub fn is_tool(&self) -> bool {`
`333`	`333`	`matches!(self, Mode::ToolBootstrap \| Mode::ToolRustc \| Mode::ToolStd)`
`334`	`334`	`}`
	`335`	`+`
	`336`	`+ pub fn must_support_dlopen(&self) -> bool {`
	`337`	`+ matches!(self, Mode::Std \| Mode::Codegen)`
	`338`	`+ }`
`335`	`339`	`}`
`336`	`340`
`337`	`341`	`impl Build {`