Simplify LTO flags handling
... and add more comments about the use of --lto-O0.
Test: presubmit
Change-Id: I2ef7bf4f100a8d7559a6b738e9211c596d579dc6
diff --git a/cc/lto.go b/cc/lto.go
index 547ebff..510dd79 100644
--- a/cc/lto.go
+++ b/cc/lto.go
@@ -76,43 +76,44 @@
return flags
}
if lto.Properties.LtoEnabled {
- var ltoCFlag string
- var ltoLdFlag string
- if lto.ThinLTO() {
- ltoCFlag = "-flto=thin -fsplit-lto-unit"
- } else {
- ltoCFlag = "-flto=thin -fsplit-lto-unit"
- ltoLdFlag = "-Wl,--lto-O0"
+ ltoCFlags := []string{"-flto=thin", "-fsplit-lto-unit"}
+ var ltoLdFlags []string
+
+ // The module did not explicitly turn on LTO. Only leverage LTO's
+ // better dead code elinmination and CFG simplification, but do
+ // not perform costly optimizations for a balance between compile
+ // time, binary size and performance.
+ if !lto.ThinLTO() {
+ ltoLdFlags = append(ltoLdFlags, "-Wl,--lto-O0")
}
- flags.Local.CFlags = append(flags.Local.CFlags, ltoCFlag)
- flags.Local.AsFlags = append(flags.Local.AsFlags, ltoCFlag)
- flags.Local.LdFlags = append(flags.Local.LdFlags, ltoCFlag)
- flags.Local.LdFlags = append(flags.Local.LdFlags, ltoLdFlag)
-
if Bool(lto.Properties.Whole_program_vtables) {
- flags.Local.CFlags = append(flags.Local.CFlags, "-fwhole-program-vtables")
+ ltoCFlags = append(ltoCFlags, "-fwhole-program-vtables")
}
if ctx.Config().IsEnvTrue("USE_THINLTO_CACHE") {
// Set appropriate ThinLTO cache policy
cacheDirFormat := "-Wl,--thinlto-cache-dir="
cacheDir := android.PathForOutput(ctx, "thinlto-cache").String()
- flags.Local.LdFlags = append(flags.Local.LdFlags, cacheDirFormat+cacheDir)
+ ltoLdFlags = append(ltoLdFlags, cacheDirFormat+cacheDir)
// Limit the size of the ThinLTO cache to the lesser of 10% of available
// disk space and 10GB.
cachePolicyFormat := "-Wl,--thinlto-cache-policy="
policy := "cache_size=10%:cache_size_bytes=10g"
- flags.Local.LdFlags = append(flags.Local.LdFlags, cachePolicyFormat+policy)
+ ltoLdFlags = append(ltoLdFlags, cachePolicyFormat+policy)
}
// If the module does not have a profile, be conservative and limit cross TU inline
// limit to 5 LLVM IR instructions, to balance binary size increase and performance.
if !ctx.Darwin() && !ctx.isPgoCompile() && !ctx.isAfdoCompile() {
- flags.Local.LdFlags = append(flags.Local.LdFlags,
- "-Wl,-plugin-opt,-import-instr-limit=5")
+ ltoLdFlags = append(ltoLdFlags, "-Wl,-plugin-opt,-import-instr-limit=5")
}
+
+ flags.Local.CFlags = append(flags.Local.CFlags, ltoCFlags...)
+ flags.Local.AsFlags = append(flags.Local.AsFlags, ltoCFlags...)
+ flags.Local.LdFlags = append(flags.Local.LdFlags, ltoCFlags...)
+ flags.Local.LdFlags = append(flags.Local.LdFlags, ltoLdFlags...)
}
return flags
}