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Don't force -O1 with ThinLTO

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This doesn't seem to be necessary anymore, although I don't know
at which point or why that changed.

Forcing -O1 makes some tests fail under NewPM, because NewPM also
performs inlining at -O1, so it ends up performing much more
optimization in practice than before.
This commit is contained in:
Nikita Popov 2021-04-05 11:12:45 +02:00
parent 7c4989ab70
commit 5519cbfe33
1 changed files with 0 additions and 22 deletions
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22
compiler/rustc_codegen_llvm/src/back/lto.rs
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@ -584,12 +584,6 @@ pub(crate) fn run_pass_manager(
if write::should_use_new_llvm_pass_manager(config) { if write::should_use_new_llvm_pass_manager(config) {
let opt_stage = if thin { llvm::OptStage::ThinLTO } else { llvm::OptStage::FatLTO }; let opt_stage = if thin { llvm::OptStage::ThinLTO } else { llvm::OptStage::FatLTO };
let opt_level = config.opt_level.unwrap_or(config::OptLevel::No); let opt_level = config.opt_level.unwrap_or(config::OptLevel::No);
// See comment below for why this is necessary.
let opt_level = if let config::OptLevel::No = opt_level {
config::OptLevel::Less
} else {
opt_level
};
write::optimize_with_new_llvm_pass_manager(cgcx, module, config, opt_level, opt_stage); write::optimize_with_new_llvm_pass_manager(cgcx, module, config, opt_level, opt_stage);
debug!("lto done"); debug!("lto done");
return; return;
@ -603,26 +597,10 @@ pub(crate) fn run_pass_manager(
llvm::LLVMRustAddPass(pm, pass.unwrap()); llvm::LLVMRustAddPass(pm, pass.unwrap());
} }
// When optimizing for LTO we don't actually pass in `-O0`, but we force
// it to always happen at least with `-O1`.
//
// With ThinLTO we mess around a lot with symbol visibility in a way
// that will actually cause linking failures if we optimize at O0 which
// notable is lacking in dead code elimination. To ensure we at least
// get some optimizations and correctly link we forcibly switch to `-O1`
// to get dead code elimination.
//
// Note that in general this shouldn't matter too much as you typically
// only turn on ThinLTO when you're compiling with optimizations
// otherwise.
let opt_level = config let opt_level = config
.opt_level .opt_level
.map(|x| to_llvm_opt_settings(x).0) .map(|x| to_llvm_opt_settings(x).0)
.unwrap_or(llvm::CodeGenOptLevel::None); .unwrap_or(llvm::CodeGenOptLevel::None);
let opt_level = match opt_level {
llvm::CodeGenOptLevel::None => llvm::CodeGenOptLevel::Less,
level => level,
};
with_llvm_pmb(module.module_llvm.llmod(), config, opt_level, false, &mut |b| { with_llvm_pmb(module.module_llvm.llmod(), config, opt_level, false, &mut |b| {
if thin { if thin {
llvm::LLVMRustPassManagerBuilderPopulateThinLTOPassManager(b, pm); llvm::LLVMRustPassManagerBuilderPopulateThinLTOPassManager(b, pm);