From 236e389be4bb7f65e78bd378143b67f401f05338 Mon Sep 17 00:00:00 2001
From: Michael Gottesman <mgottesman@apple.com>
Date: Fri, 9 Aug 2013 21:26:18 +0000
Subject: [PATCH] [stackprotector] Simplify SP Pass so that we emit different
 fail basic blocks for each fail condition.

This patch decouples the stack protector pass so that we can support stack
protector implementations that do not use the IR level generated stack protector
fail basic block.

No codesize increase is caused by this change since the MI level tail merge pass
properly merges together the fail condition blocks (see the updated test).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188105 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/StackProtector.cpp      | 20 ++++++++++----------
 test/CodeGen/X86/stack-protector.ll |  4 ++++
 2 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/lib/CodeGen/StackProtector.cpp b/lib/CodeGen/StackProtector.cpp
index 4c5638092e5..f8c98266dda 100644
--- a/lib/CodeGen/StackProtector.cpp
+++ b/lib/CodeGen/StackProtector.cpp
@@ -312,8 +312,7 @@ static void CreatePrologue(Function *F, Module *M, ReturnInst *RI,
 ///  - The epilogue checks the value stored in the prologue against the original
 ///    value. It calls __stack_chk_fail if they differ.
 bool StackProtector::InsertStackProtectors() {
-  BasicBlock *FailBB = 0;       // The basic block to jump to if check fails.
-  BasicBlock *FailBBDom = 0;    // FailBB's dominator.
+  bool HasPrologue = false;
   AllocaInst *AI = 0;           // Place on stack that stores the stack guard.
   Value *StackGuardVar = 0;  // The stack guard variable.
 
@@ -322,10 +321,9 @@ bool StackProtector::InsertStackProtectors() {
     ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
     if (!RI) continue;
 
-    if (!FailBB) {
+    if (!HasPrologue) {
+      HasPrologue = true;
       CreatePrologue(F, M, RI, TLI, Trip, AI, StackGuardVar);
-      // Create the basic block to jump to when the guard check fails.
-      FailBB = CreateFailBB();
     }
 
     // For each block with a return instruction, convert this:
@@ -350,12 +348,16 @@ bool StackProtector::InsertStackProtectors() {
     //     call void @__stack_chk_fail()
     //     unreachable
 
+    // Create the fail basic block.
+    BasicBlock *FailBB = CreateFailBB();
+
     // Split the basic block before the return instruction.
     BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");
 
+    // Update the dominator tree if we need to.
     if (DT && DT->isReachableFromEntry(BB)) {
       DT->addNewBlock(NewBB, BB);
-      FailBBDom = FailBBDom ? DT->findNearestCommonDominator(FailBBDom, BB) :BB;
+      DT->addNewBlock(FailBB, BB);
     }
 
     // Remove default branch instruction to the new BB.
@@ -374,10 +376,8 @@ bool StackProtector::InsertStackProtectors() {
 
   // Return if we didn't modify any basic blocks. I.e., there are no return
   // statements in the function.
-  if (!FailBB) return false;
-
-  if (DT && FailBBDom)
-    DT->addNewBlock(FailBB, FailBBDom);
+  if (!HasPrologue)
+    return false;
 
   return true;
 }
diff --git a/test/CodeGen/X86/stack-protector.ll b/test/CodeGen/X86/stack-protector.ll
index a4dbbb96882..265ec80682b 100644
--- a/test/CodeGen/X86/stack-protector.ll
+++ b/test/CodeGen/X86/stack-protector.ll
@@ -2313,18 +2313,22 @@ entry:
 ; LINUX-I386-LABEL: test19d:
 ; LINUX-I386: mov{{l|q}} %gs:
 ; LINUX-I386: calll __stack_chk_fail
+; LINUX-I386-NOT: calll __stack_chk_fail
 
 ; LINUX-X64-LABEL: test19d:
 ; LINUX-X64: mov{{l|q}} %fs:
 ; LINUX-X64: callq __stack_chk_fail
+; LINUX-X64-NOT: callq __stack_chk_fail
 
 ; LINUX-KERNEL-X64-LABEL: test19d:
 ; LINUX-KERNEL-X64: mov{{l|q}} %gs:
 ; LINUX-KERNEL-X64: callq __stack_chk_fail
+; LINUX-KERNEL-X64-NOT: callq ___stack_chk_fail
 
 ; DARWIN-X64-LABEL: test19d:
 ; DARWIN-X64: mov{{l|q}} ___stack_chk_guard
 ; DARWIN-X64: callq ___stack_chk_fail
+; DARWIN-X64-NOT: callq ___stack_chk_fail
   %c = alloca %struct.pair, align 4
   %exn.slot = alloca i8*
   %ehselector.slot = alloca i32