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enable parallel codegen by default

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Enable parallel codegen (2 units) by default when --opt-level is 0 or 1.  This
gives a minor speedup on large crates (~10%), with only a tiny slowdown (~2%)
for small ones (which usually build in under a second regardless).  The current
default (no parallelization) is used when the user requests optimization
(--opt-level 2 or 3), and when the user has enabled LTO (which is incompatible
with parallel codegen).

This commit also changes the rust build system to use parallel codegen
when appropriate.  This means codegen-units=4 for stage0 always, and
also for stage1 and stage2 when configured with --disable-optimize.
(Other settings use codegen-units=1 for stage1 and stage2, to get
maximum performance for release binaries.)  The build system also sets
codegen-units=1 for compiletest tests (compiletest does its own
parallelization) and uses the same setting as stage2 for crate tests.
This commit is contained in:
Stuart Pernsteiner 2014-10-06 16:59:21 -07:00 committed by Patrick Walton
parent 4764c16011
commit c245c5bbad
3 changed files with 25 additions and 1 deletions
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7
mk/main.mk
View File

@ -157,6 +157,13 @@ RUSTFLAGS_STAGE1 += -C prefer-dynamic
# by not emitting them.
RUSTFLAGS_STAGE0 += -Z no-landing-pads
# Go fast for stage0, and also for stage1/stage2 if optimization is off.
RUSTFLAGS_STAGE0 += -C codegen-units=4
ifdef CFG_DISABLE_OPTIMIZE
RUSTFLAGS_STAGE1 += -C codegen-units=4
RUSTFLAGS_STAGE2 += -C codegen-units=4
endif
# platform-specific auto-configuration
include $(CFG_SRC_DIR)mk/platform.mk

4
mk/tests.mk
View File

@ -628,6 +628,10 @@ CTEST_RUSTC_FLAGS := $$(subst -O,,$$(CTEST_RUSTC_FLAGS))
ifndef CFG_DISABLE_OPTIMIZE_TESTS
CTEST_RUSTC_FLAGS += -O
endif
# Force codegen-units=1 for compiletest tests. compiletest does its own
# parallelization internally, so rustc's default codegen-units=2 will actually
# slow things down.
CTEST_RUSTC_FLAGS += -C codegen-units=1
CTEST_COMMON_ARGS$(1)-T-$(2)-H-$(3) := \
--compile-lib-path $$(HLIB$(1)_H_$(3)) \

15
src/librustc/driver/config.rs
View File

@ -780,7 +780,20 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
early_warn("the --crate-file-name argument has been renamed to \
--print-file-name");
}
let cg = build_codegen_options(matches);
let mut cg = build_codegen_options(matches);
if cg.codegen_units == 0 {
match opt_level {
// `-C lto` doesn't work with multiple codegen units.
_ if cg.lto => cg.codegen_units = 1,
No | Less => cg.codegen_units = 2,
Default | Aggressive => cg.codegen_units = 1,
}
}
let cg = cg;
if !cg.remark.is_empty() && debuginfo == NoDebugInfo {
early_warn("-C remark will not show source locations without --debuginfo");