[stack protector] Set edge weights for newly created basic blocks.

This commit fixes a bug in stack protector pass where edge weights were not set
when new basic blocks were added to lists of successor basic blocks.

Differential Revision: http://reviews.llvm.org/D5766


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222987 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/BranchProbabilityInfo.h

@@ -111,6 +111,10 @@ public:
   void setEdgeWeight(const BasicBlock *Src, unsigned IndexInSuccessors,
                      uint32_t Weight);
 
+  static uint32_t getBranchWeightStackProtector(bool IsLikely) {
+    return IsLikely ? (1u << 20) - 1 : 1;
+  }
+
 private:
   // Since we allow duplicate edges from one basic block to another, we use
   // a pair (PredBlock and an index in the successors) to specify an edge.

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -7763,6 +7763,7 @@ MachineBasicBlock *
 SelectionDAGBuilder::StackProtectorDescriptor::
 AddSuccessorMBB(const BasicBlock *BB,
                 MachineBasicBlock *ParentMBB,
+                bool IsLikely,
                 MachineBasicBlock *SuccMBB) {
   // If SuccBB has not been created yet, create it.
   if (!SuccMBB) {
@@ -7772,6 +7773,7 @@ AddSuccessorMBB(const BasicBlock *BB,
     MF->insert(++BBI, SuccMBB);
   }
   // Add it as a successor of ParentMBB.
-  ParentMBB->addSuccessor(SuccMBB);
+  ParentMBB->addSuccessor(
+      SuccMBB, BranchProbabilityInfo::getBranchWeightStackProtector(IsLikely));
   return SuccMBB;
 }

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h

@@ -417,8 +417,8 @@ private:
       assert(!shouldEmitStackProtector() && "Stack Protector Descriptor is "
              "already initialized!");
       ParentMBB = MBB;
-      SuccessMBB = AddSuccessorMBB(BB, MBB);
-      FailureMBB = AddSuccessorMBB(BB, MBB, FailureMBB);
+      SuccessMBB = AddSuccessorMBB(BB, MBB, /* IsLikely */ true);
+      FailureMBB = AddSuccessorMBB(BB, MBB, /* IsLikely */ false, FailureMBB);
       if (!Guard)
         Guard = StackProtCheckCall.getArgOperand(0);
     }
@@ -487,9 +487,10 @@ private:
 
     /// Add a successor machine basic block to ParentMBB. If the successor mbb
     /// has not been created yet (i.e. if SuccMBB = 0), then the machine basic
-    /// block will be created.
+    /// block will be created. Assign a large weight if IsLikely is true.
     MachineBasicBlock *AddSuccessorMBB(const BasicBlock *BB,
                                        MachineBasicBlock *ParentMBB,
+                                       bool IsLikely,
                                        MachineBasicBlock *SuccMBB = nullptr);
   };
 

lib/CodeGen/StackProtector.cpp

@@ -17,6 +17,7 @@
 #include "llvm/CodeGen/StackProtector.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/CodeGen/Analysis.h"
 #include "llvm/CodeGen/Passes.h"
@@ -31,6 +32,7 @@
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/MDBuilder.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
@@ -459,7 +461,13 @@ bool StackProtector::InsertStackProtectors() {
       LoadInst *LI1 = B.CreateLoad(StackGuardVar);
       LoadInst *LI2 = B.CreateLoad(AI);
       Value *Cmp = B.CreateICmpEQ(LI1, LI2);
-      B.CreateCondBr(Cmp, NewBB, FailBB);
+      unsigned SuccessWeight =
+          BranchProbabilityInfo::getBranchWeightStackProtector(true);
+      unsigned FailureWeight =
+          BranchProbabilityInfo::getBranchWeightStackProtector(false);
+      MDNode *Weights = MDBuilder(F->getContext())
+                            .createBranchWeights(SuccessWeight, FailureWeight);
+      B.CreateCondBr(Cmp, NewBB, FailBB, Weights);
     }
   }
 

test/CodeGen/X86/stack-protector-weight.ll

@@ -0,0 +1,36 @@
+; RUN: llc -mtriple=x86_64-apple-darwin -print-machineinstrs=expand-isel-pseudos -enable-selectiondag-sp=true %s -o /dev/null 2>&1 | FileCheck %s --check-prefix=SELDAG
+; RUN: llc -mtriple=x86_64-apple-darwin -print-machineinstrs=expand-isel-pseudos -enable-selectiondag-sp=false %s -o /dev/null 2>&1 | FileCheck %s --check-prefix=IR
+
+; SELDAG: # Machine code for function test_branch_weights:
+; SELDAG: Successors according to CFG: BB#[[SUCCESS:[0-9]+]](1048575) BB#[[FAILURE:[0-9]+]](1)
+; SELDAG: BB#[[FAILURE]]:
+; SELDAG: CALL64pcrel32 <es:__stack_chk_fail>
+; SELDAG: BB#[[SUCCESS]]:
+
+; IR: # Machine code for function test_branch_weights:
+; IR: Successors according to CFG: BB#[[SUCCESS:[0-9]+]](1048575) BB#[[FAILURE:[0-9]+]](1)
+; IR: BB#[[SUCCESS]]:
+; IR: BB#[[FAILURE]]:
+; IR: CALL64pcrel32 <ga:@__stack_chk_fail>
+
+define i32 @test_branch_weights(i32 %n) #0 {
+entry:
+  %a = alloca [128 x i32], align 16
+  %0 = bitcast [128 x i32]* %a to i8*
+  call void @llvm.lifetime.start(i64 512, i8* %0)
+  %arraydecay = getelementptr inbounds [128 x i32]* %a, i64 0, i64 0
+  call void @foo2(i32* %arraydecay)
+  %idxprom = sext i32 %n to i64
+  %arrayidx = getelementptr inbounds [128 x i32]* %a, i64 0, i64 %idxprom
+  %1 = load i32* %arrayidx, align 4
+  call void @llvm.lifetime.end(i64 512, i8* %0)
+  ret i32 %1
+}
+
+declare void @llvm.lifetime.start(i64, i8* nocapture)
+
+declare void @foo2(i32*)
+
+declare void @llvm.lifetime.end(i64, i8* nocapture)
+
+attributes #0 = { ssp "stack-protector-buffer-size"="8" }