[ConstantFolding] Use FoldBitCast correctly

Previously we might attempt to use a BitCast to turn bits into vectors of pointers,
but that requires an inttoptr cast to be legal. Add an assertion to detect the formation of illegal bitcast attempts
early (in the tests, we often constant-fold away the result before getting to this assertion check),
while being careful to still handle the early-return conditions without adding extra complexity in the result.

Patch by Jameson Nash <jameson@juliacomputing.com>.

Differential Revision: https://reviews.llvm.org/D65057

llvm-svn: 372940

1 files changed, 20 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 7b3d8157780..8cad7d90a64 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -93,6 +93,9 @@ static Constant *foldConstVectorToAPInt(APInt &Result, Type *DestTy,
 /// This always returns a non-null constant, but it may be a
 /// ConstantExpr if unfoldable.
 Constant *FoldBitCast(Constant *C, Type *DestTy, const DataLayout &DL) {
+  assert(CastInst::castIsValid(Instruction::BitCast, C, DestTy) &&
+         "Invalid constantexpr bitcast!");
+
   // Catch the obvious splat cases.
   if (C->isNullValue() && !DestTy->isX86_MMXTy())
     return Constant::getNullValue(DestTy);
@@ -521,8 +524,23 @@ Constant *FoldReinterpretLoadFromConstPtr(Constant *C, Type *LoadTy,
       return nullptr;
 
     C = FoldBitCast(C, MapTy->getPointerTo(AS), DL);
-    if (Constant *Res = FoldReinterpretLoadFromConstPtr(C, MapTy, DL))
-      return FoldBitCast(Res, LoadTy, DL);
+    if (Constant *Res = FoldReinterpretLoadFromConstPtr(C, MapTy, DL)) {
+      if (Res->isNullValue() && !LoadTy->isX86_MMXTy())
+        // Materializing a zero can be done trivially without a bitcast
+        return Constant::getNullValue(LoadTy);
+      Type *CastTy = LoadTy->isPtrOrPtrVectorTy() ? DL.getIntPtrType(LoadTy) : LoadTy;
+      Res = FoldBitCast(Res, CastTy, DL);
+      if (LoadTy->isPtrOrPtrVectorTy()) {
+        // For vector of pointer, we needed to first convert to a vector of integer, then do vector inttoptr
+        if (Res->isNullValue() && !LoadTy->isX86_MMXTy())
+          return Constant::getNullValue(LoadTy);
+        if (DL.isNonIntegralPointerType(LoadTy->getScalarType()))
+          // Be careful not to replace a load of an addrspace value with an inttoptr here
+          return nullptr;
+        Res = ConstantExpr::getCast(Instruction::IntToPtr, Res, LoadTy);
+      }
+      return Res;
+    }
     return nullptr;
   }