Stop emitting non-power-of-two vectors in basic LLVM codegen

scottmcm · scottmcm · commit 84e305dd93cc · 2023-08-25T20:06:57.000-07:00
diff --git a/compiler/rustc_codegen_llvm/src/type_of.rs b/compiler/rustc_codegen_llvm/src/type_of.rs
@@ -405,7 +405,11 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyAndLayout<'tcx> {
 
         // Vectors, even for non-power-of-two sizes, have the same layout as
         // arrays but don't count as aggregate types
+        // While LLVM theoretically supports non-power-of-two sizes, and they
+        // often work fine, sometimes x86-isel deals with them horribly
+        // (see #115212) so for now only use power-of-two ones.
         if let FieldsShape::Array { count, .. } = self.layout.fields()
+            && count.is_power_of_two()
             && let element = self.field(cx, 0)
             && element.ty.is_integral()
         {
diff --git a/tests/codegen/mem-replace-simple-type.rs b/tests/codegen/mem-replace-simple-type.rs
@@ -33,12 +33,21 @@ pub fn replace_ref_str<'a>(r: &mut &'a str, v: &'a str) -> &'a str {
 }
 
 #[no_mangle]
-// CHECK-LABEL: @replace_short_array(
-pub fn replace_short_array(r: &mut [u32; 3], v: [u32; 3]) -> [u32; 3] {
+// CHECK-LABEL: @replace_short_array_3(
+pub fn replace_short_array_3(r: &mut [u32; 3], v: [u32; 3]) -> [u32; 3] {
     // CHECK-NOT: alloca
-    // CHECK: %[[R:.+]] = load <3 x i32>, ptr %r, align 4
-    // CHECK: store <3 x i32> %[[R]], ptr %result
-    // CHECK: %[[V:.+]] = load <3 x i32>, ptr %v, align 4
-    // CHECK: store <3 x i32> %[[V]], ptr %r
+    // CHECK: call void @llvm.memcpy.p0.p0.i64(ptr align 4 %result, ptr align 4 %r, i64 12, i1 false)
+    // CHECK: call void @llvm.memcpy.p0.p0.i64(ptr align 4 %r, ptr align 4 %v, i64 12, i1 false)
+    std::mem::replace(r, v)
+}
+
+#[no_mangle]
+// CHECK-LABEL: @replace_short_array_4(
+pub fn replace_short_array_4(r: &mut [u32; 4], v: [u32; 4]) -> [u32; 4] {
+    // CHECK-NOT: alloca
+    // CHECK: %[[R:.+]] = load <4 x i32>, ptr %r, align 4
+    // CHECK: store <4 x i32> %[[R]], ptr %result
+    // CHECK: %[[V:.+]] = load <4 x i32>, ptr %v, align 4
+    // CHECK: store <4 x i32> %[[V]], ptr %r
     std::mem::replace(r, v)
 }
diff --git a/tests/codegen/swap-small-types.rs b/tests/codegen/swap-small-types.rs
@@ -11,11 +11,12 @@ type RGB48 = [u16; 3];
 // CHECK-LABEL: @swap_rgb48_manually(
 #[no_mangle]
 pub fn swap_rgb48_manually(x: &mut RGB48, y: &mut RGB48) {
-    // CHECK-NOT: alloca
-    // CHECK: %[[TEMP0:.+]] = load <3 x i16>, ptr %x, align 2
-    // CHECK: %[[TEMP1:.+]] = load <3 x i16>, ptr %y, align 2
-    // CHECK: store <3 x i16> %[[TEMP1]], ptr %x, align 2
-    // CHECK: store <3 x i16> %[[TEMP0]], ptr %y, align 2
+    // FIXME: See #115212 for why this has an alloca again
+
+    // CHECK: alloca [3 x i16], align 2
+    // CHECK: call void @llvm.memcpy.p0.p0.i64({{.+}}, i64 6, i1 false)
+    // CHECK: call void @llvm.memcpy.p0.p0.i64({{.+}}, i64 6, i1 false)
+    // CHECK: call void @llvm.memcpy.p0.p0.i64({{.+}}, i64 6, i1 false)
 
     let temp = *x;
     *x = *y;
@@ -25,11 +26,25 @@ pub fn swap_rgb48_manually(x: &mut RGB48, y: &mut RGB48) {
 // CHECK-LABEL: @swap_rgb48
 #[no_mangle]
 pub fn swap_rgb48(x: &mut RGB48, y: &mut RGB48) {
+    // FIXME: See #115212 for why this has an alloca again
+
+    // CHECK: alloca [3 x i16], align 2
+    // CHECK: call void @llvm.memcpy.p0.p0.i64({{.+}}, i64 6, i1 false)
+    // CHECK: call void @llvm.memcpy.p0.p0.i64({{.+}}, i64 6, i1 false)
+    // CHECK: call void @llvm.memcpy.p0.p0.i64({{.+}}, i64 6, i1 false)
+    swap(x, y)
+}
+
+type RGBA64 = [u16; 4];
+
+// CHECK-LABEL: @swap_rgba64
+#[no_mangle]
+pub fn swap_rgba64(x: &mut RGBA64, y: &mut RGBA64) {
     // CHECK-NOT: alloca
-    // CHECK: load <3 x i16>
-    // CHECK: load <3 x i16>
-    // CHECK: store <3 x i16>
-    // CHECK: store <3 x i16>
+    // CHECK-DAG: %[[XVAL:.+]] = load <4 x i16>, ptr %x, align 2
+    // CHECK-DAG: %[[YVAL:.+]] = load <4 x i16>, ptr %y, align 2
+    // CHECK-DAG: store <4 x i16> %[[YVAL]], ptr %x, align 2
+    // CHECK-DAG: store <4 x i16> %[[XVAL]], ptr %y, align 2
     swap(x, y)
 }
 
