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From 0f5ee28213a73733e6811b176c89ecececfe9cbc Mon Sep 17 00:00:00 2001
From: bors <bors@rust-lang.org>
Date: Mon, 11 Sep 2017 12:53:21 +0000
Subject: [PATCH] Auto merge of #44440 - cuviper:min_global_align,
 r=japaric

Add `TargetOptions::min_global_align`, with s390x at 16-bit

The SystemZ `LALR` instruction provides PC-relative addressing for globals,
but only to *even* addresses, so other compilers make sure that such
globals are always 2-byte aligned.  In Clang, this is modeled with
`TargetInfo::MinGlobalAlign`, and `TargetOptions::min_global_align` now
serves the same purpose for rustc.

In Clang, the only targets that set this are SystemZ, Lanai, and NVPTX, and
the latter two don't have targets in rust master.

Fixes #44411.
r? @eddyb
---
 src/librustc_back/target/mod.rs                    |  6 ++++
 .../target/s390x_unknown_linux_gnu.rs              |  1 +
 src/librustc_trans/consts.rs                       | 24 ++++++++++++--
 src/test/run-make/min-global-align/Makefile        | 22 +++++++++++++
 .../run-make/min-global-align/min_global_align.rs  | 38 ++++++++++++++++++++++
 5 files changed, 89 insertions(+), 2 deletions(-)
 create mode 100644 src/test/run-make/min-global-align/Makefile
 create mode 100644 src/test/run-make/min-global-align/min_global_align.rs

diff --git a/src/librustc_back/target/mod.rs b/src/librustc_back/target/mod.rs
index 130e1b695dbd..301cf3f8c820 100644
--- a/src/librustc_back/target/mod.rs
+++ b/src/librustc_back/target/mod.rs
@@ -425,6 +425,9 @@ pub struct TargetOptions {
 
     /// Whether or not stack probes (__rust_probestack) are enabled
     pub stack_probes: bool,
+
+    /// The minimum alignment for global symbols.
+    pub min_global_align: Option<u64>,
 }
 
 impl Default for TargetOptions {
@@ -486,6 +489,7 @@ impl Default for TargetOptions {
             crt_static_default: false,
             crt_static_respected: false,
             stack_probes: false,
+            min_global_align: None,
         }
     }
 }
@@ -724,6 +728,7 @@ impl Target {
         key!(crt_static_default, bool);
         key!(crt_static_respected, bool);
         key!(stack_probes, bool);
+        key!(min_global_align, Option<u64>);
 
         if let Some(array) = obj.find("abi-blacklist").and_then(Json::as_array) {
             for name in array.iter().filter_map(|abi| abi.as_string()) {
@@ -914,6 +919,7 @@ impl ToJson for Target {
         target_option_val!(crt_static_default);
         target_option_val!(crt_static_respected);
         target_option_val!(stack_probes);
+        target_option_val!(min_global_align);
 
         if default.abi_blacklist != self.options.abi_blacklist {
             d.insert("abi-blacklist".to_string(), self.options.abi_blacklist.iter()
diff --git a/src/librustc_back/target/s390x_unknown_linux_gnu.rs b/src/librustc_back/target/s390x_unknown_linux_gnu.rs
index 78a6bb7933d9..aad9effacd44 100644
--- a/src/librustc_back/target/s390x_unknown_linux_gnu.rs
+++ b/src/librustc_back/target/s390x_unknown_linux_gnu.rs
@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
     base.max_atomic_width = Some(64);
     // see #36994
     base.exe_allocation_crate = None;
+    base.min_global_align = Some(16);
 
     Ok(Target {
         llvm_target: "s390x-unknown-linux-gnu".to_string(),
diff --git a/src/librustc_trans/consts.rs b/src/librustc_trans/consts.rs
index 310cd6fe9559..f7f9b9386841 100644
--- a/src/librustc_trans/consts.rs
+++ b/src/librustc_trans/consts.rs
@@ -26,6 +26,7 @@ use rustc::ty;
 
 use rustc::hir;
 
+use std::cmp;
 use std::ffi::{CStr, CString};
 use syntax::ast;
 use syntax::attr;
@@ -42,6 +43,25 @@ pub fn bitcast(val: ValueRef, ty: Type) -> ValueRef {
     }
 }
 
+fn set_global_alignment(ccx: &CrateContext,
+                        gv: ValueRef,
+                        mut align: machine::llalign) {
+    // The target may require greater alignment for globals than the type does.
+    // Note: GCC and Clang also allow `__attribute__((aligned))` on variables,
+    // which can force it to be smaller.  Rust doesn't support this yet.
+    if let Some(min) = ccx.sess().target.target.options.min_global_align {
+        match ty::layout::Align::from_bits(min, min) {
+            Ok(min) => align = cmp::max(align, min.abi() as machine::llalign),
+            Err(err) => {
+                ccx.sess().err(&format!("invalid minimum global alignment: {}", err));
+            }
+        }
+    }
+    unsafe {
+        llvm::LLVMSetAlignment(gv, align);
+    }
+}
+
 pub fn addr_of_mut(ccx: &CrateContext,
                    cv: ValueRef,
                    align: machine::llalign,
@@ -53,7 +73,7 @@ pub fn addr_of_mut(ccx: &CrateContext,
             bug!("symbol `{}` is already defined", name);
         });
         llvm::LLVMSetInitializer(gv, cv);
-        llvm::LLVMSetAlignment(gv, align);
+        set_global_alignment(ccx, gv, align);
         llvm::LLVMRustSetLinkage(gv, llvm::Linkage::InternalLinkage);
         SetUnnamedAddr(gv, true);
         gv
@@ -271,7 +291,7 @@ pub fn trans_static<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
             ccx.statics_to_rauw().borrow_mut().push((g, new_g));
             new_g
         };
-        llvm::LLVMSetAlignment(g, ccx.align_of(ty));
+        set_global_alignment(ccx, g, ccx.align_of(ty));
         llvm::LLVMSetInitializer(g, v);
 
         // As an optimization, all shared statics which do not have interior
diff --git a/src/test/run-make/min-global-align/Makefile b/src/test/run-make/min-global-align/Makefile
new file mode 100644
index 000000000000..2eacc36f380d
--- /dev/null
+++ b/src/test/run-make/min-global-align/Makefile
@@ -0,0 +1,22 @@
+-include ../tools.mk
+
+# This tests ensure that global variables respect the target minimum alignment.
+# The three bools `STATIC_BOOL`, `STATIC_MUT_BOOL`, and `CONST_BOOL` all have
+# type-alignment of 1, but some targets require greater global alignment.
+
+SRC = min_global_align.rs
+LL = $(TMPDIR)/min_global_align.ll
+
+all:
+ifeq ($(UNAME),Linux)
+# Most targets are happy with default alignment -- take i686 for example.
+ifeq ($(filter x86,$(LLVM_COMPONENTS)),x86)
+	$(RUSTC) --target=i686-unknown-linux-gnu --emit=llvm-ir $(SRC)
+	[ "$$(grep -c 'align 1' "$(LL)")" -eq "3" ]
+endif
+# SystemZ requires even alignment for PC-relative addressing.
+ifeq ($(filter systemz,$(LLVM_COMPONENTS)),systemz)
+	$(RUSTC) --target=s390x-unknown-linux-gnu --emit=llvm-ir $(SRC)
+	[ "$$(grep -c 'align 2' "$(LL)")" -eq "3" ]
+endif
+endif
diff --git a/src/test/run-make/min-global-align/min_global_align.rs b/src/test/run-make/min-global-align/min_global_align.rs
new file mode 100644
index 000000000000..3d4f9001a747
--- /dev/null
+++ b/src/test/run-make/min-global-align/min_global_align.rs
@@ -0,0 +1,38 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(no_core, lang_items)]
+#![crate_type="rlib"]
+#![no_core]
+
+pub static STATIC_BOOL: bool = true;
+
+pub static mut STATIC_MUT_BOOL: bool = true;
+
+const CONST_BOOL: bool = true;
+pub static CONST_BOOL_REF: &'static bool = &CONST_BOOL;
+
+
+#[lang = "sized"]
+trait Sized {}
+
+#[lang = "copy"]
+trait Copy {}
+
+#[lang = "freeze"]
+trait Freeze {}
+
+#[lang = "sync"]
+trait Sync {}
+impl Sync for bool {}
+impl Sync for &'static bool {}
+
+#[lang="drop_in_place"]
+pub unsafe fn drop_in_place<T: ?Sized>(_: *mut T) { }
-- 
2.13.5