[PATCH] D18414: [PS4] Guarantee an instruction after a 'noreturn' call

[Paul Robinson via llvm-commits]

probinson created this revision.
probinson added a reviewer: rnk.
probinson added a subscriber: llvm-commits.

Enable the TargetMachine's TrapUnreachable flag for PS4.

We need the "return address" of a noreturn call to be within the
bounds of the calling function; TrapUnreachable turns 'unreachable'
into a 'ud2' instruction, which has that desired effect.

(I know Reid made several attempts to remove this, months ago.
But it's still there, and we need something, so we'd like to turn it on
for PS4 as well as Windows.  We'd be equally happy with a (hypothetical)
NopUnreachable, or something more specific to 'noreturn', but this is a
cheap and easy solution that meets our needs.)


http://reviews.llvm.org/D18414

Files:
  lib/Target/X86/X86TargetMachine.cpp
  test/CodeGen/X86/br-fold.ll
  test/CodeGen/X86/ps4-noreturn.ll

Index: test/CodeGen/X86/ps4-noreturn.ll
===================================================================
--- test/CodeGen/X86/ps4-noreturn.ll
+++ test/CodeGen/X86/ps4-noreturn.ll
@@ -0,0 +1,38 @@
+; RUN: llc < %s -mtriple=x86_64-scei-ps4 | FileCheck %s
+
+declare i32 @personality(...)
+
+; Check that after the (implicitly noreturn) unwind call, there is
+; another instruction. It was easy to produce 'ud2' so we check for that.
+define void @foo1() personality i32 (...)* @personality {
+; CHECK-LABEL: foo1:
+; CHECK: .cfi_startproc
+; CHECK: callq bar
+; CHECK: retq
+; Check for 'ud2' between noreturn call and function end.
+; CHECK: callq _Unwind_Resume
+; CHECK-NEXT: ud2
+; CHECK-NEXT: .Lfunc_end0:
+    invoke void @bar()
+        to label %normal
+        unwind label %catch
+normal:
+    ret void
+catch:
+    %1 = landingpad { i8*, i32 } cleanup
+    resume { i8*, i32 } %1
+}
+
+declare void @bar() #0
+
+; Similar check after an explicit noreturn call.
+define void @foo2() {
+; CHECK-LABEL: foo2:
+; CHECK: callq bar
+; CHECK-NEXT: ud2
+; CHECK-NEXT: .Lfunc_end1:
+    tail call void @bar()
+    unreachable
+}
+
+attributes #0 = { noreturn }
Index: test/CodeGen/X86/br-fold.ll
===================================================================
--- test/CodeGen/X86/br-fold.ll
+++ test/CodeGen/X86/br-fold.ll
@@ -2,6 +2,7 @@
 ; RUN: llc -mtriple=x86_64-pc-linux < %s | FileCheck  -check-prefix=X64_LINUX %s
 ; RUN: llc -mtriple=x86_64-pc-windows < %s | FileCheck  -check-prefix=X64_WINDOWS %s
 ; RUN: llc -mtriple=x86_64-pc-windows-gnu < %s | FileCheck  -check-prefix=X64_WINDOWS_GNU %s
+; RUN: llc -mtriple=x86_64-scei-ps4 < %s | FileCheck -check-prefix=PS4 %s
 
 ; X64_DARWIN: orq
 ; X64_DARWIN-NEXT: %bb8.i329
@@ -15,6 +16,9 @@
 ; X64_WINDOWS_GNU: orq %rax, %rcx
 ; X64_WINDOWS_GNU-NEXT: ud2
 
+; PS4: orq %rax, %rcx
+; PS4-NEXT: ud2
+
 @_ZN11xercesc_2_513SchemaSymbols21fgURI_SCHEMAFORSCHEMAE = external constant [33 x i16], align 32 ; <[33 x i16]*> [#uses=1]
 @_ZN11xercesc_2_56XMLUni16fgNotationStringE = external constant [9 x i16], align 16 ; <[9 x i16]*> [#uses=1]
 
Index: lib/Target/X86/X86TargetMachine.cpp
===================================================================
--- lib/Target/X86/X86TargetMachine.cpp
+++ lib/Target/X86/X86TargetMachine.cpp
@@ -119,7 +119,9 @@
   // after a call to 'noreturn' function.
   // To prevent that, we emit a trap for 'unreachable' IR instructions.
   // (which on X86, happens to be the 'ud2' instruction)
-  if (Subtarget.isTargetWin64())
+  // On PS4, the "return address" of a 'noreturn' call must still be within
+  // the calling function, and TrapUnreachable is an easy way to get that.
+  if (Subtarget.isTargetWin64() || Subtarget.isTargetPS4())
     this->Options.TrapUnreachable = true;
 
   // By default (and when -ffast-math is on), enable estimate codegen for


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