From 722aa9573bf4d6b1a0b29fd3bd573fefafc20ebb Mon Sep 17 00:00:00 2001
From: Quentin Colombet <qcolombet@apple.com>
Date: Fri, 10 Jul 2015 22:09:55 +0000
Subject: [PATCH] [ShrinkWrap][PEI] Do not insert epilogue for unreachable
 blocks.

Although this is not incorrect to insert such code, it is useless
and it hurts the binary size.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241946 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/PrologEpilogInserter.cpp          | 11 ++++--
 test/CodeGen/AArch64/arm64-shrink-wrapping.ll | 39 +++++++++++++++++++
 test/CodeGen/X86/x86-shrink-wrapping.ll       | 39 +++++++++++++++++++
 3 files changed, 86 insertions(+), 3 deletions(-)

diff --git a/lib/CodeGen/PrologEpilogInserter.cpp b/lib/CodeGen/PrologEpilogInserter.cpp
index 76583f0de88..7e162332de6 100644
--- a/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/lib/CodeGen/PrologEpilogInserter.cpp
@@ -92,7 +92,7 @@ private:
   void insertPrologEpilogCode(MachineFunction &Fn);
 
   // Convenience for recognizing return blocks.
-  bool isReturnBlock(MachineBasicBlock *MBB);
+  bool isReturnBlock(const MachineBasicBlock *MBB) const;
 };
 } // namespace
 
@@ -127,7 +127,7 @@ void PEI::getAnalysisUsage(AnalysisUsage &AU) const {
   MachineFunctionPass::getAnalysisUsage(AU);
 }
 
-bool PEI::isReturnBlock(MachineBasicBlock* MBB) {
+bool PEI::isReturnBlock(const MachineBasicBlock* MBB) const {
   return (MBB && !MBB->empty() && MBB->back().isReturn());
 }
 
@@ -143,7 +143,12 @@ void PEI::calculateSets(MachineFunction &Fn) {
   if (MFI->getSavePoint()) {
     SaveBlock = MFI->getSavePoint();
     assert(MFI->getRestorePoint() && "Both restore and save must be set");
-    RestoreBlocks.push_back(MFI->getRestorePoint());
+    MachineBasicBlock *RestoreBlock = MFI->getRestorePoint();
+    // If RestoreBlock does not have any successor and is not a return block
+    // then the end point is unreachable and we do not need to insert any
+    // epilogue.
+    if (!RestoreBlock->succ_empty() || isReturnBlock(RestoreBlock))
+      RestoreBlocks.push_back(RestoreBlock);
     return;
   }
 
diff --git a/test/CodeGen/AArch64/arm64-shrink-wrapping.ll b/test/CodeGen/AArch64/arm64-shrink-wrapping.ll
index c1777513fa0..599712be401 100644
--- a/test/CodeGen/AArch64/arm64-shrink-wrapping.ll
+++ b/test/CodeGen/AArch64/arm64-shrink-wrapping.ll
@@ -500,3 +500,42 @@ if.end:                                           ; preds = %if.else, %if.then
 }
 
 declare i32 @someVariadicFunc(i32, ...)
+
+; Make sure we do not insert unreachable code after noreturn function.
+; Although this is not incorrect to insert such code, it is useless
+; and it hurts the binary size.
+;
+; CHECK-LABEL: noreturn:
+; DISABLE: stp
+;
+; CHECK: and [[TEST:w[0-9]+]], w0, #0xff
+; CHECK-NEXT: cbnz [[TEST]], [[ABORT:LBB[0-9_]+]]
+;
+; CHECK: movz w0, #0x2a
+;
+; DISABLE-NEXT: ldp
+;
+; CHECK-NEXT: ret
+;
+; CHECK: [[ABORT]]: ; %if.abort
+;
+; ENABLE: stp
+;
+; CHECK: bl _abort
+; ENABLE-NOT: ldp
+define i32 @noreturn(i8 signext %bad_thing) {
+entry:
+  %tobool = icmp eq i8 %bad_thing, 0
+  br i1 %tobool, label %if.end, label %if.abort
+
+if.abort:
+  tail call void @abort() #0
+  unreachable
+
+if.end:
+  ret i32 42
+}
+
+declare void @abort() #0
+
+attributes #0 = { noreturn nounwind }
diff --git a/test/CodeGen/X86/x86-shrink-wrapping.ll b/test/CodeGen/X86/x86-shrink-wrapping.ll
index 5848eddf437..8c91335d91a 100644
--- a/test/CodeGen/X86/x86-shrink-wrapping.ll
+++ b/test/CodeGen/X86/x86-shrink-wrapping.ll
@@ -598,3 +598,42 @@ if.then.60:                                       ; preds = %if.end.55
 cleanup:                                          ; preds = %if.then.60, %if.end.55, %lor.lhs.false, %lor.lhs.false, %lor.lhs.false, %lor.lhs.false, %lor.lhs.false, %lor.lhs.false, %lor.lhs.false, %lor.lhs.false, %if.end, %entry
   ret void
 }
+
+; Make sure we do not insert unreachable code after noreturn function.
+; Although this is not incorrect to insert such code, it is useless
+; and it hurts the binary size.
+;
+; CHECK-LABEL: noreturn:
+; DISABLE: pushq
+;
+; CHECK: testb   %dil, %dil
+; CHECK-NEXT: jne      [[ABORT:LBB[0-9_]+]]
+;
+; CHECK: movl $42, %eax
+;
+; DISABLE-NEXT: popq
+;
+; CHECK-NEXT: retq
+;
+; CHECK: [[ABORT]]: ## %if.abort
+;
+; ENABLE: pushq
+;
+; CHECK: callq _abort
+; ENABLE-NOT: popq
+define i32 @noreturn(i8 signext %bad_thing) {
+entry:
+  %tobool = icmp eq i8 %bad_thing, 0
+  br i1 %tobool, label %if.end, label %if.abort
+
+if.abort:
+  tail call void @abort() #0
+  unreachable
+
+if.end:
+  ret i32 42
+}
+
+declare void @abort() #0
+
+attributes #0 = { noreturn nounwind }
-- 
2.34.1