[llvm] 3db8a3e - [InstCombine] avoid crash from deleting an instruction that still has uses (PR43723) (3rd try)

[Sanjay Patel via llvm-commits]

Author: Sanjay Patel
Date: 2019-11-11T09:29:40-05:00
New Revision: 3db8a3ef86e7b3331ab466a78c10a62be9e69829

URL: https://github.com/llvm/llvm-project/commit/3db8a3ef86e7b3331ab466a78c10a62be9e69829
DIFF: https://github.com/llvm/llvm-project/commit/3db8a3ef86e7b3331ab466a78c10a62be9e69829.diff

LOG: [InstCombine] avoid crash from deleting an instruction that still has uses (PR43723) (3rd try)

Re-try because earlier attempts were reverted due to use-after-free.
Hopefully, diagnosed correctly this time - we replace/remove the
invariant.start first rather than the invariant.end to avoid angering
worklist-based iteration.

We gather a set of white-listed instructions in isAllocSiteRemovable() and then
replace/erase them. But we don't know in general if the instructions in the set
have uses amongst themselves, so order of deletion makes a difference.

There's already a special-case for the llvm.objectsize intrinsic, so add another
for llvm.invariant.start.

Should fix:
https://bugs.llvm.org/show_bug.cgi?id=43723

Differential Revision: https://reviews.llvm.org/D69977

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
    llvm/test/Transforms/InstCombine/builtin-object-size-ptr.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index b1828d0fe32b..3b137c3f1c3b 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2340,13 +2340,21 @@ static bool isAllocSiteRemovable(Instruction *AI,
               return false;
             LLVM_FALLTHROUGH;
           }
-          case Intrinsic::invariant_start:
           case Intrinsic::invariant_end:
           case Intrinsic::lifetime_start:
           case Intrinsic::lifetime_end:
           case Intrinsic::objectsize:
             Users.emplace_back(I);
             continue;
+          case Intrinsic::invariant_start:
+            // Only delete this if it has no uses or a single 'end' use.
+            if (I->use_empty())
+              Users.emplace_back(I);
+            else if (I->hasOneUse() &&
+                     match(I->user_back(),
+                           m_Intrinsic<Intrinsic::invariant_end>()))
+              Users.emplace_back(I);
+            continue;
           }
         }
 
@@ -2394,14 +2402,13 @@ Instruction *InstCombiner::visitAllocSite(Instruction &MI) {
 
   if (isAllocSiteRemovable(&MI, Users, &TLI)) {
     for (unsigned i = 0, e = Users.size(); i != e; ++i) {
-      // Lowering all @llvm.objectsize calls first because they may
-      // use a bitcast/GEP of the alloca we are removing.
       if (!Users[i])
        continue;
 
       Instruction *I = cast<Instruction>(&*Users[i]);
-
       if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
+        // Lowering all @llvm.objectsize calls first because they may
+        // use a bitcast/GEP of the alloca we are removing.
         if (II->getIntrinsicID() == Intrinsic::objectsize) {
           Value *Result =
               lowerObjectSizeCall(II, DL, &TLI, /*MustSucceed=*/true);
@@ -2409,6 +2416,13 @@ Instruction *InstCombiner::visitAllocSite(Instruction &MI) {
           eraseInstFromFunction(*I);
           Users[i] = nullptr; // Skip examining in the next loop.
         }
+        // Erase llvm.invariant.start because we expect that it is used by
+        // llvm.invariant.end that we will remove below.
+        if (II->getIntrinsicID() == Intrinsic::invariant_start) {
+          replaceInstUsesWith(*I, UndefValue::get(I->getType()));
+          eraseInstFromFunction(*I);
+          Users[i] = nullptr; // Skip examining in the next loop.
+        }
       }
     }
     for (unsigned i = 0, e = Users.size(); i != e; ++i) {

diff  --git a/llvm/test/Transforms/InstCombine/builtin-object-size-ptr.ll b/llvm/test/Transforms/InstCombine/builtin-object-size-ptr.ll
index 4475e9554a53..261176f45764 100644
--- a/llvm/test/Transforms/InstCombine/builtin-object-size-ptr.ll
+++ b/llvm/test/Transforms/InstCombine/builtin-object-size-ptr.ll
@@ -28,6 +28,41 @@ define i32 @foo() #0 {
   ret i32 %conv
 }
 
+; This used to crash while erasing instructions:
+; https://bugs.llvm.org/show_bug.cgi?id=43723
+
+define void @PR43723() {
+; CHECK-LABEL: @PR43723(
+; CHECK-NEXT:    ret void
+;
+  %tab = alloca [10 x i8], align 16
+  %t0 = bitcast [10 x i8]* %tab to i8*
+  call void @llvm.memset.p0i8.i64(i8* align 16 %t0, i8 9, i64 10, i1 false)
+  %t1 = call {}* @llvm.invariant.start.p0i8(i64 10, i8* align 16 %t0)
+  call void @llvm.invariant.end.p0i8({}* %t1, i64 10, i8* align 16 %t0)
+  ret void
+
+  uselistorder i8* %t0, { 1, 0, 2 }
+}
+
+define void @unknown_use_of_invariant_start({}** %p) {
+; CHECK-LABEL: @unknown_use_of_invariant_start(
+; CHECK-NEXT:    [[T1:%.*]] = call {}* @llvm.invariant.start.p0i8(i64 10, i8* align 16 undef)
+; CHECK-NEXT:    store {}* [[T1]], {}** [[P:%.*]], align 8
+; CHECK-NEXT:    ret void
+;
+  %tab = alloca [10 x i8], align 16
+  %t0 = bitcast [10 x i8]* %tab to i8*
+  call void @llvm.memset.p0i8.i64(i8* align 16 %t0, i8 9, i64 10, i1 false)
+  %t1 = call {}* @llvm.invariant.start.p0i8(i64 10, i8* align 16 %t0)
+  call void @llvm.invariant.end.p0i8({}* %t1, i64 10, i8* align 16 %t0)
+  store {}* %t1, {}** %p
+  ret void
+}
+
 declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture) #1
 declare i64 @llvm.objectsize.i64.p0i8(i8*, i1) #2
 declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture) #1
+declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i1 immarg) #0
+declare {}* @llvm.invariant.start.p0i8(i64 immarg, i8* nocapture) #0
+declare void @llvm.invariant.end.p0i8({}*, i64 immarg, i8* nocapture) #0