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: [PATCH] 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 ++++++++++++++--------
 .../Transforms/SimplifyCFG/sink-common-code.ll     | 21 +++++++++++++---
 2 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index c7c66fd..ec5db1e 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;
diff --git a/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll b/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll
index a2639d8..953d96e 100644
--- a/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll
+++ b/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll
@@ -340,7 +340,7 @@ if.end:
 ; CHECK-LABEL: test13
 ; CHECK-DAG: select
 ; CHECK-DAG: load volatile
-; CHECK: store volatile {{.*}}, !tbaa !0
+; CHECK: store volatile {{.*}}, !tbaa ![[TBAA:[0-9]]]
 ; CHECK-NOT: load
 ; CHECK-NOT: store
 
@@ -384,6 +384,7 @@ if.else:
   %gepb = getelementptr inbounds %struct.anon, %struct.anon* %s, i32 0, i32 1
   %sv2 = load i32, i32* %gepb
   %cmp2 = icmp eq i32 %sv2, 57
+  call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !9, metadata !DIExpression()), !dbg !11
   br label %if.end
 
 if.end:
@@ -391,6 +392,18 @@ if.end:
   ret i32 1
 }
 
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+!llvm.module.flags = !{!5, !6}
+!llvm.dbg.cu = !{!7}
+
+!5 = !{i32 2, !"Dwarf Version", i32 4}
+!6 = !{i32 2, !"Debug Info Version", i32 3}
+!7 = distinct !DICompileUnit(language: DW_LANG_C99, file: !10)
+!8 = distinct !DISubprogram(name: "foo", unit: !7)
+!9 = !DILocalVariable(name: "b", line: 1, arg: 2, scope: !8)
+!10 = !DIFile(filename: "a.c", directory: "a/b")
+!11 = !DILocation(line: 1, column: 14, scope: !8)
+
 ; CHECK-LABEL: test14
 ; CHECK: getelementptr
 ; CHECK: load
@@ -781,6 +794,6 @@ merge:
 ; CHECK: right:
 ; CHECK-NEXT:   %val1 = call i32 @call_target() [ "deopt"(i32 20) ]
 
-; CHECK: !0 = !{!1, !1, i64 0}
-; CHECK: !1 = !{!"float", !2}
-; CHECK: !2 = !{!"an example type tree"}
+; CHECK: ![[TBAA]] = !{![[TYPE:[0-9]]], ![[TYPE]], i64 0}
+; CHECK: ![[TYPE]] = !{!"float", ![[TEXT:[0-9]]]}
+; CHECK: ![[TEXT]] = !{!"an example type tree"}
-- 
2.7.4