From 5b96ae7106e04606c67588d55927e88653529ec7 Mon Sep 17 00:00:00 2001
From: clubby789 <jamie@hill-daniel.co.uk>
Date: Sun, 25 Feb 2024 22:56:08 +0000
Subject: [PATCH] Don't codegen `expect` in opt-level=0

---
 compiler/rustc_codegen_llvm/src/intrinsic.rs    | 17 ++++++++++-------
 compiler/rustc_codegen_ssa/src/mir/rvalue.rs    |  2 +-
 compiler/rustc_codegen_ssa/src/mir/statement.rs |  7 ++-----
 tests/codegen/intrinsics/likely.rs              |  2 +-
 4 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
index a300f5f707a88..05fb77a193af3 100644
--- a/compiler/rustc_codegen_llvm/src/intrinsic.rs
+++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -187,9 +187,7 @@ impl<'ll, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'_, 'll, 'tcx> {
                     Some(instance),
                 )
             }
-            sym::likely => {
-                self.call_intrinsic("llvm.expect.i1", &[args[0].immediate(), self.const_bool(true)])
-            }
+            sym::likely => self.expect(args[0].immediate(), true),
             sym::is_val_statically_known => {
                 let intrinsic_type = args[0].layout.immediate_llvm_type(self.cx);
                 let kind = self.type_kind(intrinsic_type);
@@ -210,8 +208,7 @@ impl<'ll, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'_, 'll, 'tcx> {
                     self.const_bool(false)
                 }
             }
-            sym::unlikely => self
-                .call_intrinsic("llvm.expect.i1", &[args[0].immediate(), self.const_bool(false)]),
+            sym::unlikely => self.expect(args[0].immediate(), false),
             sym::select_unpredictable => {
                 let cond = args[0].immediate();
                 assert_eq!(args[1].layout, args[2].layout);
@@ -604,11 +601,17 @@ impl<'ll, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'_, 'll, 'tcx> {
     }
 
     fn assume(&mut self, val: Self::Value) {
-        self.call_intrinsic("llvm.assume", &[val]);
+        if self.cx.sess().opts.optimize != rustc_session::config::OptLevel::No {
+            self.call_intrinsic("llvm.assume", &[val]);
+        }
     }
 
     fn expect(&mut self, cond: Self::Value, expected: bool) -> Self::Value {
-        self.call_intrinsic("llvm.expect.i1", &[cond, self.const_bool(expected)])
+        if self.cx.sess().opts.optimize != rustc_session::config::OptLevel::No {
+            self.call_intrinsic("llvm.expect.i1", &[cond, self.const_bool(expected)])
+        } else {
+            cond
+        }
     }
 
     fn type_test(&mut self, pointer: Self::Value, typeid: Self::Value) -> Self::Value {
diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
index d94c6f8ddcec3..91fd9905f63cc 100644
--- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
@@ -382,7 +382,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         scalar: abi::Scalar,
         backend_ty: Bx::Type,
     ) {
-        if matches!(self.cx.sess().opts.optimize, OptLevel::No | OptLevel::Less)
+        if matches!(self.cx.sess().opts.optimize, OptLevel::No)
             // For now, the critical niches are all over `Int`eger values.
             // Should floating-point values or pointers ever get more complex
             // niches, then this code will probably want to handle them too.
diff --git a/compiler/rustc_codegen_ssa/src/mir/statement.rs b/compiler/rustc_codegen_ssa/src/mir/statement.rs
index 2ef860fc336d6..73283cafb4947 100644
--- a/compiler/rustc_codegen_ssa/src/mir/statement.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/statement.rs
@@ -1,6 +1,5 @@
 use rustc_middle::mir::{self, NonDivergingIntrinsic};
 use rustc_middle::span_bug;
-use rustc_session::config::OptLevel;
 use tracing::instrument;
 
 use super::{FunctionCx, LocalRef};
@@ -68,10 +67,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 self.codegen_coverage(bx, kind, statement.source_info.scope);
             }
             mir::StatementKind::Intrinsic(box NonDivergingIntrinsic::Assume(ref op)) => {
-                if !matches!(bx.tcx().sess.opts.optimize, OptLevel::No | OptLevel::Less) {
-                    let op_val = self.codegen_operand(bx, op);
-                    bx.assume(op_val.immediate());
-                }
+                let op_val = self.codegen_operand(bx, op);
+                bx.assume(op_val.immediate());
             }
             mir::StatementKind::Intrinsic(box NonDivergingIntrinsic::CopyNonOverlapping(
                 mir::CopyNonOverlapping { ref count, ref src, ref dst },
diff --git a/tests/codegen/intrinsics/likely.rs b/tests/codegen/intrinsics/likely.rs
index 098fd9936ce17..9dc31d210454b 100644
--- a/tests/codegen/intrinsics/likely.rs
+++ b/tests/codegen/intrinsics/likely.rs
@@ -1,4 +1,4 @@
-//@ compile-flags: -C no-prepopulate-passes
+//@ compile-flags: -C no-prepopulate-passes -Copt-level=1
 
 #![crate_type = "lib"]
 #![feature(core_intrinsics)]