[PATCH] [ARM64] Prefer generation of bzero on Darwin only

[Bradley Smith]

Hi t.p.northover,

This patch modifies the behavior of the ARM64 backend to only prefer generating bzero for zero memsets when the target is Darwin, since not all target libraries will have this function. This matches the behavior of x86 (almost, x86 is MacOSX >= 10.6 however for ARM64 I believe that just checking for Darwin should be sufficient), no other backends use bzero.

http://reviews.llvm.org/D3585

Files:
  lib/Target/ARM64/ARM64Subtarget.cpp
  test/CodeGen/ARM64/memset-to-bzero.ll

Index: lib/Target/ARM64/ARM64Subtarget.cpp
===================================================================
--- lib/Target/ARM64/ARM64Subtarget.cpp
+++ lib/Target/ARM64/ARM64Subtarget.cpp
@@ -90,8 +90,11 @@
 /// memset with zero passed as the second argument. Otherwise it
 /// returns null.
 const char *ARM64Subtarget::getBZeroEntry() const {
-  // At the moment, always prefer bzero.
-  return "bzero";
+  // Prefer bzero on Darwin only.
+  if(isTargetDarwin())
+    return "bzero";
+
+  return nullptr;
 }
 
 void ARM64Subtarget::overrideSchedPolicy(MachineSchedPolicy &Policy,
Index: test/CodeGen/ARM64/memset-to-bzero.ll
===================================================================
--- test/CodeGen/ARM64/memset-to-bzero.ll
+++ test/CodeGen/ARM64/memset-to-bzero.ll
@@ -1,4 +1,7 @@
-; RUN: llc %s -march arm64 -o - | FileCheck %s
+; RUN: llc %s -mtriple=arm64-apple-darwin -o - | \
+; RUN:   FileCheck --check-prefix=CHECK-DARWIN --check-prefix=CHECK %s
+; RUN: llc %s -mtriple=arm64-linux-gnu -o - | \
+; RUN:   FileCheck --check-prefix=CHECK-LINUX --check-prefix=CHECK %s
 ; <rdar://problem/14199482> ARM64: Calls to bzero() replaced with calls to memset()
 
 ; CHECK: @fct1
@@ -14,16 +17,18 @@
 
 ; CHECK: @fct2
 ; When the size is bigger than 256, change into bzero.
-; CHECK: bzero
+; CHECK-DARWIN: bzero
+; CHECK-LINUX: memset
 define void @fct2(i8* nocapture %ptr) {
 entry:
   tail call void @llvm.memset.p0i8.i64(i8* %ptr, i8 0, i64 257, i32 1, i1 false)
   ret void
 }
 
 ; CHECK: @fct3
 ; For unknown size, change to bzero.
-; CHECK: bzero
+; CHECK-DARWIN: bzero
+; CHECK-LINUX: memset
 define void @fct3(i8* nocapture %ptr, i32 %unknown) {
 entry:
   %conv = sext i32 %unknown to i64
@@ -47,7 +52,8 @@
 
 ; CHECK: @fct5
 ; Size > 256, change.
-; CHECK: bzero
+; CHECK-DARWIN: bzero
+; CHECK-LINUX: memset
 define void @fct5(i8* %ptr) {
 entry:
   %tmp = tail call i64 @llvm.objectsize.i64(i8* %ptr, i1 false)
@@ -57,7 +63,8 @@
 
 ; CHECK: @fct6
 ; Size = unknown, change.
-; CHECK: bzero
+; CHECK-DARWIN: bzero
+; CHECK-LINUX: memset
 define void @fct6(i8* %ptr, i32 %unknown) {
 entry:
   %conv = sext i32 %unknown to i64
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