[MS ABI] Some code cleanups

Don't create unnecessary truncations if the result will not be used.
Also prefer preforming math before the truncation, it makes it a little
easier to reason about.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@274984 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/MicrosoftCXXABI.cpp b/lib/CodeGen/MicrosoftCXXABI.cpp
index e86d7eb77351128a1a9bf55d2396885e9fcb355d..93a6f000e39a6daa1f8bfab45eacaaec68505008 100644 (file)
--- a/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -942,7 +942,6 @@ MicrosoftCXXABI::performBaseAdjustment(CodeGenFunction &CGF, Address Value,
   llvm::Value *Offset =
     GetVirtualBaseClassOffset(CGF, Value, SrcDecl, PolymorphicBase);
   llvm::Value *Ptr = CGF.Builder.CreateInBoundsGEP(Value.getPointer(), Offset);
-  Offset = CGF.Builder.CreateTrunc(Offset, CGF.Int32Ty);
   CharUnits VBaseAlign =
     CGF.CGM.getVBaseAlignment(Value.getAlignment(), SrcDecl, PolymorphicBase);
   return std::make_pair(Address(Ptr, VBaseAlign), Offset);
@@ -976,8 +975,8 @@ llvm::Value *MicrosoftCXXABI::EmitTypeid(CodeGenFunction &CGF,
                                          QualType SrcRecordTy,
                                          Address ThisPtr,
                                          llvm::Type *StdTypeInfoPtrTy) {
-  llvm::Value *Offset;
-  std::tie(ThisPtr, Offset) = performBaseAdjustment(CGF, ThisPtr, SrcRecordTy);
+  std::tie(ThisPtr, std::ignore) =
+      performBaseAdjustment(CGF, ThisPtr, SrcRecordTy);
   auto Typeid = emitRTtypeidCall(CGF, ThisPtr.getPointer()).getInstruction();
   return CGF.Builder.CreateBitCast(Typeid, StdTypeInfoPtrTy);
 }
@@ -1002,6 +1001,7 @@ llvm::Value *MicrosoftCXXABI::EmitDynamicCastCall(
   llvm::Value *Offset;
   std::tie(This, Offset) = performBaseAdjustment(CGF, This, SrcRecordTy);
   llvm::Value *ThisPtr = This.getPointer();
+  Offset = CGF.Builder.CreateTrunc(Offset, CGF.Int32Ty);
 
   // PVOID __RTDynamicCast(
   //   PVOID inptr,
@@ -1025,8 +1025,7 @@ llvm::Value *
 MicrosoftCXXABI::EmitDynamicCastToVoid(CodeGenFunction &CGF, Address Value,
                                        QualType SrcRecordTy,
                                        QualType DestTy) {
-  llvm::Value *Offset;
-  std::tie(Value, Offset) = performBaseAdjustment(CGF, Value, SrcRecordTy);
+  std::tie(Value, std::ignore) = performBaseAdjustment(CGF, Value, SrcRecordTy);
 
   // PVOID __RTCastToVoid(
   //   PVOID inptr)
@@ -1152,16 +1151,14 @@ void MicrosoftCXXABI::initializeHiddenVirtualInheritanceMembers(
 
     llvm::Value *VBaseOffset =
         GetVirtualBaseClassOffset(CGF, getThisAddress(CGF), RD, I->first);
-    // FIXME: it doesn't look right that we SExt in GetVirtualBaseClassOffset()
-    // just to Trunc back immediately.
-    VBaseOffset = Builder.CreateTruncOrBitCast(VBaseOffset, CGF.Int32Ty);
     uint64_t ConstantVBaseOffset =
         Layout.getVBaseClassOffset(I->first).getQuantity();
 
     // vtorDisp_for_vbase = vbptr[vbase_idx] - offsetof(RD, vbase).
     llvm::Value *VtorDispValue = Builder.CreateSub(
-        VBaseOffset, llvm::ConstantInt::get(CGM.Int32Ty, ConstantVBaseOffset),
+        VBaseOffset, llvm::ConstantInt::get(CGM.PtrDiffTy, ConstantVBaseOffset),
         "vtordisp.value");
+    VtorDispValue = Builder.CreateTruncOrBitCast(VtorDispValue, CGF.Int32Ty);
 
     if (!Int8This)
       Int8This = Builder.CreateBitCast(getThisValue(CGF),