From 018a3afa99573586646e36d6e3e20e59975466bb Mon Sep 17 00:00:00 2001
From: Dehao Chen <dehao@google.com>
Date: Mon, 17 Oct 2016 19:28:44 +0000
Subject: Ignore debug info when making optimization decisions in SimplifyCFG.

Summary: Debug info should *not* affect code generation. This patch properly handles debug info to make sure the generated code are the same with or without debug info.

Reviewers: davidxl, mzolotukhin, jmolloy

Subscribers: aprantl, llvm-commits

Differential Revision: https://reviews.llvm.org/D25286

llvm-svn: 284415
---
 llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

(limited to 'llvm/lib/Transforms/Utils/SimplifyCFG.cpp')

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index c7c66fd9d74..ec5db1e5744 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1485,8 +1485,14 @@ static bool sinkLastInstruction(ArrayRef<BasicBlock*> Blocks) {
   // canSinkLastInstruction returning true guarantees that every block has at
   // least one non-terminator instruction.
   SmallVector<Instruction*,4> Insts;
-  for (auto *BB : Blocks)
-    Insts.push_back(BB->getTerminator()->getPrevNode());
+  for (auto *BB : Blocks) {
+    Instruction *I = BB->getTerminator();
+    do {
+      I = I->getPrevNode();
+    } while (isa<DbgInfoIntrinsic>(I) && I != &BB->front());
+    if (!isa<DbgInfoIntrinsic>(I))
+      Insts.push_back(I);
+  }
 
   // The only checking we need to do now is that all users of all instructions
   // are the same PHI node. canSinkLastInstruction should have checked this but
@@ -1584,15 +1590,15 @@ namespace {
       Fail = false;
       Insts.clear();
       for (auto *BB : Blocks) {
-        if (Instruction *Terminator = BB->getTerminator()) {
-          if (Instruction *LastNonTerminator = Terminator->getPrevNode()) {
-            Insts.push_back(LastNonTerminator);
-            continue;
-          }
+        Instruction *Inst = BB->getTerminator();
+        for (Inst = Inst->getPrevNode(); Inst && isa<DbgInfoIntrinsic>(Inst);)
+          Inst = Inst->getPrevNode();
+        if (!Inst) {
+          // Block wasn't big enough.
+          Fail = true;
+          return;
         }
-        // Block wasn't big enough.
-        Fail = true;
-        return;
+        Insts.push_back(Inst);
       }
     }
 
@@ -1604,7 +1610,8 @@ namespace {
       if (Fail)
         return;
       for (auto *&Inst : Insts) {
-        Inst = Inst->getPrevNode();
+        for (Inst = Inst->getPrevNode(); Inst && isa<DbgInfoIntrinsic>(Inst);)
+          Inst = Inst->getPrevNode();
         // Already at beginning of block.
         if (!Inst) {
           Fail = true;
-- 
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