Emit getelementptr inbounds nuw for pointer::add()

Author: nikic

compiler/rustc_codegen_llvm/src/builder.rs

@@ -32,7 +32,9 @@ use crate::abi::FnAbiLlvmExt;
 use crate::attributes;
 use crate::common::Funclet;
 use crate::context::{CodegenCx, SimpleCx};
-use crate::llvm::{self, AtomicOrdering, AtomicRmwBinOp, BasicBlock, False, GEPNoWrapFlags, Metadata, True};
+use crate::llvm::{
+    self, AtomicOrdering, AtomicRmwBinOp, BasicBlock, False, GEPNoWrapFlags, Metadata, True,
+};
 use crate::type_::Type;
 use crate::type_of::LayoutLlvmExt;
 use crate::value::Value;
@@ -939,6 +941,25 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         }
     }
 
+    fn inbounds_nuw_gep(
+        &mut self,
+        ty: &'ll Type,
+        ptr: &'ll Value,
+        indices: &[&'ll Value],
+    ) -> &'ll Value {
+        unsafe {
+            llvm::LLVMBuildGEPWithNoWrapFlags(
+                self.llbuilder,
+                ty,
+                ptr,
+                indices.as_ptr(),
+                indices.len() as c_uint,
+                UNNAMED,
+                GEPNoWrapFlags::InBounds | GEPNoWrapFlags::NUW,
+            )
+        }
+    }
+
     /* Casts */
     fn trunc(&mut self, val: &'ll Value, dest_ty: &'ll Type) -> &'ll Value {
         unsafe { llvm::LLVMBuildTrunc(self.llbuilder, val, dest_ty, UNNAMED) }

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -664,9 +664,15 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         lhs.layout.ty,
                     ),
 
-                    (OperandValue::Immediate(lhs_val), OperandValue::Immediate(rhs_val)) => {
-                        self.codegen_scalar_binop(bx, op, lhs_val, rhs_val, lhs.layout.ty)
-                    }
+                    (OperandValue::Immediate(lhs_val), OperandValue::Immediate(rhs_val)) => self
+                        .codegen_scalar_binop(
+                            bx,
+                            op,
+                            lhs_val,
+                            rhs_val,
+                            lhs.layout.ty,
+                            rhs.layout.ty,
+                        ),
 
                     _ => bug!(),
                 };
@@ -887,10 +893,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         op: mir::BinOp,
         lhs: Bx::Value,
         rhs: Bx::Value,
-        input_ty: Ty<'tcx>,
+        lhs_ty: Ty<'tcx>,
+        rhs_ty: Ty<'tcx>,
     ) -> Bx::Value {
-        let is_float = input_ty.is_floating_point();
-        let is_signed = input_ty.is_signed();
+        let is_float = lhs_ty.is_floating_point();
+        let is_signed = lhs_ty.is_signed();
         match op {
             mir::BinOp::Add => {
                 if is_float {
@@ -956,17 +963,21 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             mir::BinOp::BitAnd => bx.and(lhs, rhs),
             mir::BinOp::BitXor => bx.xor(lhs, rhs),
             mir::BinOp::Offset => {
-                let pointee_type = input_ty
+                let pointee_type = lhs_ty
                     .builtin_deref(true)
-                    .unwrap_or_else(|| bug!("deref of non-pointer {:?}", input_ty));
+                    .unwrap_or_else(|| bug!("deref of non-pointer {:?}", lhs_ty));
                 let pointee_layout = bx.cx().layout_of(pointee_type);
                 if pointee_layout.is_zst() {
                     // `Offset` works in terms of the size of pointee,
                     // so offsetting a pointer to ZST is a noop.
                     lhs
                 } else {
                     let llty = bx.cx().backend_type(pointee_layout);
-                    bx.inbounds_gep(llty, lhs, &[rhs])
+                    if !rhs_ty.is_signed() {
+                        bx.inbounds_nuw_gep(llty, lhs, &[rhs])
+                    } else {
+                        bx.inbounds_gep(llty, lhs, &[rhs])
+                    }
                 }
             }
             mir::BinOp::Shl | mir::BinOp::ShlUnchecked => {

compiler/rustc_codegen_ssa/src/traits/builder.rs

@@ -332,6 +332,14 @@ pub trait BuilderMethods<'a, 'tcx>:
         ptr: Self::Value,
         indices: &[Self::Value],
     ) -> Self::Value;
+    fn inbounds_nuw_gep(
+        &mut self,
+        ty: Self::Type,
+        ptr: Self::Value,
+        indices: &[Self::Value],
+    ) -> Self::Value {
+        self.inbounds_gep(ty, ptr, indices)
+    }
     fn ptradd(&mut self, ptr: Self::Value, offset: Self::Value) -> Self::Value {
         self.gep(self.cx().type_i8(), ptr, &[offset])
     }

tests/codegen/gep-index.rs

@@ -18,7 +18,7 @@ fn index_on_struct(a: &[Foo], index: usize) -> &Foo {
 // CHECK-LABEL: @offset_on_struct(
 #[no_mangle]
 fn offset_on_struct(a: *const Foo, index: usize) -> *const Foo {
-    // CHECK: getelementptr inbounds %Foo, ptr %a, {{i64|i32}} %index
+    // CHECK: getelementptr inbounds{{( nuw)?}} %Foo, ptr %a, {{i64|i32}} %index
     unsafe { a.add(index) }
 }
 
@@ -32,6 +32,6 @@ fn index_on_i32(a: &[i32], index: usize) -> &i32 {
 // CHECK-LABEL: @offset_on_i32(
 #[no_mangle]
 fn offset_on_i32(a: *const i32, index: usize) -> *const i32 {
-    // CHECK: getelementptr inbounds i32, ptr %a, {{i64|i32}} %index
+    // CHECK: getelementptr inbounds{{( nuw)?}} i32, ptr %a, {{i64|i32}} %index
     unsafe { a.add(index) }
 }

tests/codegen/intrinsics/offset.rs

@@ -27,7 +27,7 @@ pub unsafe fn offset_isize(p: *const u32, d: isize) -> *const u32 {
 // CHECK-SAME: (ptr noundef %p, [[SIZE]] noundef %d)
 #[no_mangle]
 pub unsafe fn offset_usize(p: *const u64, d: usize) -> *const u64 {
-    // CHECK: %[[R:.*]] = getelementptr inbounds i64, ptr %p, [[SIZE]] %d
+    // CHECK: %[[R:.*]] = getelementptr inbounds{{( nuw)?}} i64, ptr %p, [[SIZE]] %d
     // CHECK-NEXT: ret ptr %[[R]]
     offset(p, d)
 }

tests/codegen/intrinsics/ptr_metadata.rs

@@ -28,7 +28,7 @@ pub unsafe fn dyn_byte_offset(
     p: *const dyn std::fmt::Debug,
     n: usize,
 ) -> *const dyn std::fmt::Debug {
-    // CHECK: %[[Q:.+]] = getelementptr inbounds i8, ptr %p.0, i64 %n
+    // CHECK: %[[Q:.+]] = getelementptr inbounds{{( nuw)?}} i8, ptr %p.0, i64 %n
     // CHECK: %[[TEMP1:.+]] = insertvalue { ptr, ptr } poison, ptr %[[Q]], 0
     // CHECK: %[[TEMP2:.+]] = insertvalue { ptr, ptr } %[[TEMP1]], ptr %p.1, 1
     // CHECK: ret { ptr, ptr } %[[TEMP2]]

tests/codegen/ptr-arithmetic.rs

@@ -6,7 +6,7 @@
 // CHECK-SAME: [[WORD:i[0-9]+]] noundef %n)
 #[no_mangle]
 pub unsafe fn i32_add(p: *const i32, n: usize) -> *const i32 {
-    // CHECK: %[[TEMP:.+]] = getelementptr inbounds i32, ptr %p, [[WORD]] %n
+    // CHECK: %[[TEMP:.+]] = getelementptr inbounds{{( nuw)?}} i32, ptr %p, [[WORD]] %n
     // CHECK: ret ptr %[[TEMP]]
     p.add(n)
 }