Auto merge of rust-lang#121614 - clubby789:no-expect, r=saethlin

Don't emit `expect`/`assume` in opt-level=0

LLVM does not make use of expect/assume calls in `opt-level=0`, so we can simplify IR by not emitting them in this case.

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 {

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.

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 },

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)]