[llvm] r263011 - Reland r262337 "calculate builtin_object_size if arg is a removable pointer"

[Petar Jovanovic via llvm-commits]

Author: petarj
Date: Wed Mar  9 08:12:47 2016
New Revision: 263011

URL: http://llvm.org/viewvc/llvm-project?rev=263011&view=rev
Log:
Reland r262337 "calculate builtin_object_size if arg is a removable pointer"

Original commit message:
 calculate builtin_object_size if argument is a removable pointer

 This patch fixes calculating correct value for builtin_object_size function
 when pointer is used only in builtin_object_size function call and never
 after that.

 Patch by Strahinja Petrovic.

 Differential Revision: http://reviews.llvm.org/D17337

Reland the original change with a small modification (first do a null check
and then do the cast) to satisfy ubsan.

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

Modified: llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp?rev=263011&r1=263010&r2=263011&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp Wed Mar  9 08:12:47 2016
@@ -1942,8 +1942,31 @@ Instruction *InstCombiner::visitAllocSit
   SmallVector<WeakVH, 64> Users;
   if (isAllocSiteRemovable(&MI, Users, TLI)) {
     for (unsigned i = 0, e = Users.size(); i != e; ++i) {
-      Instruction *I = cast_or_null<Instruction>(&*Users[i]);
-      if (!I) continue;
+      // 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)) {
+        if (II->getIntrinsicID() == Intrinsic::objectsize) {
+          uint64_t Size;
+          if (!getObjectSize(II->getArgOperand(0), Size, DL, TLI)) {
+            ConstantInt *CI = cast<ConstantInt>(II->getArgOperand(1));
+            Size = CI->isZero() ? -1ULL : 0;
+          }
+          replaceInstUsesWith(*I, ConstantInt::get(I->getType(), Size));
+          eraseInstFromFunction(*I);
+          Users[i] = nullptr; // Skip examining in the next loop.
+        }
+      }
+    }
+    for (unsigned i = 0, e = Users.size(); i != e; ++i) {
+      if (!Users[i])
+        continue;
+
+      Instruction *I = cast<Instruction>(&*Users[i]);
 
       if (ICmpInst *C = dyn_cast<ICmpInst>(I)) {
         replaceInstUsesWith(*C,
@@ -1951,12 +1974,6 @@ Instruction *InstCombiner::visitAllocSit
                                              C->isFalseWhenEqual()));
       } else if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I)) {
         replaceInstUsesWith(*I, UndefValue::get(I->getType()));
-      } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
-        if (II->getIntrinsicID() == Intrinsic::objectsize) {
-          ConstantInt *CI = cast<ConstantInt>(II->getArgOperand(1));
-          uint64_t DontKnow = CI->isZero() ? -1ULL : 0;
-          replaceInstUsesWith(*I, ConstantInt::get(I->getType(), DontKnow));
-        }
       }
       eraseInstFromFunction(*I);
     }

Added: llvm/trunk/test/Transforms/InstCombine/builtin-object-size-ptr.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/builtin-object-size-ptr.ll?rev=263011&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/builtin-object-size-ptr.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/builtin-object-size-ptr.ll Wed Mar  9 08:12:47 2016
@@ -0,0 +1,34 @@
+; RUN: opt -instcombine -S < %s | FileCheck %s
+
+; int foo() {
+; struct V { char buf1[10];
+;            int b;
+;            char buf2[10];
+;           } var;
+;
+;           char *p = &var.buf1[1];
+;           return __builtin_object_size (p, 0);
+; }
+
+%struct.V = type { [10 x i8], i32, [10 x i8] }
+
+define i32 @foo() #0 {
+entry:
+  %var = alloca %struct.V, align 4
+  %0 = bitcast %struct.V* %var to i8*
+  call void @llvm.lifetime.start(i64 28, i8* %0) #3
+  %buf1 = getelementptr inbounds %struct.V, %struct.V* %var, i32 0, i32 0
+  %arrayidx = getelementptr inbounds [10 x i8], [10 x i8]* %buf1, i64 0, i64 1
+  %1 = call i64 @llvm.objectsize.i64.p0i8(i8* %arrayidx, i1 false)
+  %conv = trunc i64 %1 to i32
+  call void @llvm.lifetime.end(i64 28, i8* %0) #3
+  ret i32 %conv
+; CHECK: ret i32 27
+; CHECK-NOT: ret i32 -1
+}
+
+declare void @llvm.lifetime.start(i64, i8* nocapture) #1
+
+declare i64 @llvm.objectsize.i64.p0i8(i8*, i1) #2
+
+declare void @llvm.lifetime.end(i64, i8* nocapture) #1