[Evaluator] Evaluate load/store with bitcast

Differential revision: https://reviews.llvm.org/D43457

llvm-svn: 327381

diff --git a/llvm/include/llvm/Analysis/ConstantFolding.h b/llvm/include/llvm/Analysis/ConstantFolding.h
index 6d4eef4..354b557 100644 (file)
--- a/llvm/include/llvm/Analysis/ConstantFolding.h
+++ b/llvm/include/llvm/Analysis/ConstantFolding.h
@@ -147,6 +147,12 @@ Constant *ConstantFoldCall(ImmutableCallSite CS, Function *F,
                            ArrayRef<Constant *> Operands,
                            const TargetLibraryInfo *TLI = nullptr);
 
+/// ConstantFoldLoadThroughBitcast - try to cast constant to destination type
+/// returning null if unsuccessful. Can cast pointer to pointer or pointer to
+/// integer and vice versa if their sizes are equal.
+Constant *ConstantFoldLoadThroughBitcast(Constant *C, Type *DestTy,
+                                         const DataLayout &DL);
+
 /// \brief Check whether the given call has no side-effects.
 /// Specifically checks for math routimes which sometimes set errno.
 bool isMathLibCallNoop(CallSite CS, const TargetLibraryInfo *TLI);

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index ace7131..c778438 100644 (file)
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -320,6 +320,41 @@ bool llvm::IsConstantOffsetFromGlobal(Constant *C, GlobalValue *&GV,
   return true;
 }
 
+Constant *llvm::ConstantFoldLoadThroughBitcast(Constant *C, Type *DestTy,
+                                         const DataLayout &DL) {
+  do {
+    Type *SrcTy = C->getType();
+
+    // If the type sizes are the same and a cast is legal, just directly
+    // cast the constant.
+    if (DL.getTypeSizeInBits(DestTy) == DL.getTypeSizeInBits(SrcTy)) {
+      Instruction::CastOps Cast = Instruction::BitCast;
+      // If we are going from a pointer to int or vice versa, we spell the cast
+      // differently.
+      if (SrcTy->isIntegerTy() && DestTy->isPointerTy())
+        Cast = Instruction::IntToPtr;
+      else if (SrcTy->isPointerTy() && DestTy->isIntegerTy())
+        Cast = Instruction::PtrToInt;
+
+      if (CastInst::castIsValid(Cast, C, DestTy))
+        return ConstantExpr::getCast(Cast, C, DestTy);
+    }
+
+    // If this isn't an aggregate type, there is nothing we can do to drill down
+    // and find a bitcastable constant.
+    if (!SrcTy->isAggregateType())
+      return nullptr;
+
+    // We're simulating a load through a pointer that was bitcast to point to
+    // a different type, so we can try to walk down through the initial
+    // elements of an aggregate to see if some part of th e aggregate is
+    // castable to implement the "load" semantic model.
+    C = C->getAggregateElement(0u);
+  } while (C);
+
+  return nullptr;
+}
+
 namespace {
 
 /// Recursive helper to read bits out of global. C is the constant being copied
@@ -537,8 +572,8 @@ Constant *FoldReinterpretLoadFromConstPtr(Constant *C, Type *LoadTy,
   return ConstantInt::get(IntType->getContext(), ResultVal);
 }
 
-Constant *ConstantFoldLoadThroughBitcast(ConstantExpr *CE, Type *DestTy,
-                                         const DataLayout &DL) {
+Constant *ConstantFoldLoadThroughBitcastExpr(ConstantExpr *CE, Type *DestTy,
+                                             const DataLayout &DL) {
   auto *SrcPtr = CE->getOperand(0);
   auto *SrcPtrTy = dyn_cast<PointerType>(SrcPtr->getType());
   if (!SrcPtrTy)
@@ -549,37 +584,7 @@ Constant *ConstantFoldLoadThroughBitcast(ConstantExpr *CE, Type *DestTy,
   if (!C)
     return nullptr;
 
-  do {
-    Type *SrcTy = C->getType();
-
-    // If the type sizes are the same and a cast is legal, just directly
-    // cast the constant.
-    if (DL.getTypeSizeInBits(DestTy) == DL.getTypeSizeInBits(SrcTy)) {
-      Instruction::CastOps Cast = Instruction::BitCast;
-      // If we are going from a pointer to int or vice versa, we spell the cast
-      // differently.
-      if (SrcTy->isIntegerTy() && DestTy->isPointerTy())
-        Cast = Instruction::IntToPtr;
-      else if (SrcTy->isPointerTy() && DestTy->isIntegerTy())
-        Cast = Instruction::PtrToInt;
-
-      if (CastInst::castIsValid(Cast, C, DestTy))
-        return ConstantExpr::getCast(Cast, C, DestTy);
-    }
-
-    // If this isn't an aggregate type, there is nothing we can do to drill down
-    // and find a bitcastable constant.
-    if (!SrcTy->isAggregateType())
-      return nullptr;
-
-    // We're simulating a load through a pointer that was bitcast to point to
-    // a different type, so we can try to walk down through the initial
-    // elements of an aggregate to see if some part of th e aggregate is
-    // castable to implement the "load" semantic model.
-    C = C->getAggregateElement(0u);
-  } while (C);
-
-  return nullptr;
+  return llvm::ConstantFoldLoadThroughBitcast(C, DestTy, DL);
 }
 
 } // end anonymous namespace
@@ -611,7 +616,7 @@ Constant *llvm::ConstantFoldLoadFromConstPtr(Constant *C, Type *Ty,
   }
 
   if (CE->getOpcode() == Instruction::BitCast)
-    if (Constant *LoadedC = ConstantFoldLoadThroughBitcast(CE, Ty, DL))
+    if (Constant *LoadedC = ConstantFoldLoadThroughBitcastExpr(CE, Ty, DL))
       return LoadedC;
 
   // Instead of loading constant c string, use corresponding integer value

diff --git a/llvm/lib/Transforms/Utils/Evaluator.cpp b/llvm/lib/Transforms/Utils/Evaluator.cpp
index 3c5e299..51fc423 100644 (file)
--- a/llvm/lib/Transforms/Utils/Evaluator.cpp
+++ b/llvm/lib/Transforms/Utils/Evaluator.cpp
@@ -174,6 +174,11 @@ static bool isSimpleEnoughPointerToCommit(Constant *C) {
   return false;
 }
 
+static Constant *getInitializer(Constant *C) {
+  auto *GV = dyn_cast<GlobalVariable>(C);
+  return GV && GV->hasDefinitiveInitializer() ? GV->getInitializer() : nullptr;
+}
+
 /// Return the value that would be computed by a load from P after the stores
 /// reflected by 'memory' have been performed.  If we can't decide, return null.
 Constant *Evaluator::ComputeLoadResult(Constant *P) {
@@ -189,14 +194,21 @@ Constant *Evaluator::ComputeLoadResult(Constant *P) {
     return nullptr;
   }
 
-  // Handle a constantexpr getelementptr.
-  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P))
-    if (CE->getOpcode() == Instruction::GetElementPtr &&
-        isa<GlobalVariable>(CE->getOperand(0))) {
-      GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
-      if (GV->hasDefinitiveInitializer())
-        return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
+  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) {
+    switch (CE->getOpcode()) {
+    // Handle a constantexpr getelementptr.
+    case Instruction::GetElementPtr:
+      if (auto *I = getInitializer(CE->getOperand(0)))
+        return ConstantFoldLoadThroughGEPConstantExpr(I, CE);
+      break;
+    // Handle a constantexpr bitcast.
+    case Instruction::BitCast:
+      if (auto *I = getInitializer(CE->getOperand(0)))
+        return ConstantFoldLoadThroughBitcast(
+            I, P->getType()->getPointerElementType(), DL);
+      break;
     }
+  }
 
   return nullptr;  // don't know how to evaluate.
 }
@@ -252,7 +264,8 @@ bool Evaluator::EvaluateBlock(BasicBlock::iterator CurInst,
           // In order to push the bitcast onto the stored value, a bitcast
           // from NewTy to Val's type must be legal.  If it's not, we can try
           // introspecting NewTy to find a legal conversion.
-          while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) {
+          Constant *NewVal;
+          while (!(NewVal = ConstantFoldLoadThroughBitcast(Val, NewTy, DL))) {
             // If NewTy is a struct, we can convert the pointer to the struct
             // into a pointer to its first member.
             // FIXME: This could be extended to support arrays as well.
@@ -276,10 +289,7 @@ bool Evaluator::EvaluateBlock(BasicBlock::iterator CurInst,
             }
           }
 
-          // If we found compatible types, go ahead and push the bitcast
-          // onto the stored value.
-          Val = ConstantExpr::getBitCast(Val, NewTy);
-
+          Val = NewVal;
           DEBUG(dbgs() << "Evaluated bitcast: " << *Val << "\n");
         }
       }

diff --git a/llvm/test/Transforms/GlobalOpt/evaluate-bitcast.ll b/llvm/test/Transforms/GlobalOpt/evaluate-bitcast.ll
new file mode 100644 (file)
index 0000000..740dba2
--- /dev/null
+++ b/llvm/test/Transforms/GlobalOpt/evaluate-bitcast.ll
@@ -0,0 +1,28 @@
+; RUN: opt -globalopt -instcombine %s -S -o - | FileCheck %s
+
+; Static constructor should have been optimized out
+; CHECK:       i32 @main
+; CHECK-NEXT:     ret i32 69905
+; CHECK-NOT:   _GLOBAL__sub_I_main.cpp
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-linux-gnu"
+
+%struct.S = type { %struct.A* }
+%struct.A = type { i64, i64 }
+
+@s = internal local_unnamed_addr global %struct.S zeroinitializer, align 8
+@llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 65535, void ()* @_GLOBAL__sub_I_main.cpp, i8* null }]
+@gA = available_externally dso_local local_unnamed_addr global %struct.A* inttoptr (i64 69905 to %struct.A*), align 8
+
+define dso_local i32 @main() local_unnamed_addr {
+  %1 = load i64, i64* bitcast (%struct.S* @s to i64*), align 8
+  %2 = trunc i64 %1 to i32
+  ret i32 %2
+}
+
+define internal void @_GLOBAL__sub_I_main.cpp() section ".text.startup" {
+  %1 = load i64, i64* bitcast (%struct.A** @gA to i64*), align 8
+  store i64 %1, i64* bitcast (%struct.S* @s to i64*), align 8
+  ret void
+}