[clang][bytecode] Pass (float) BitWidth to DoBitCast

clang/lib/AST/ByteCode/BitcastBuffer.h

@@ -45,6 +45,7 @@ struct Bits {
   bool operator>=(Bits Other) const { return N >= Other.N; }
   bool operator<=(Bits Other) const { return N <= Other.N; }
   bool operator==(Bits Other) const { return N == Other.N; }
+  bool operator!=(Bits Other) const { return N != Other.N; }
 };
 
 /// A quantity in bytes.

clang/lib/AST/ByteCode/Interp.h

@@ -14,6 +14,7 @@
 #define LLVM_CLANG_AST_INTERP_INTERP_H
 
 #include "../ExprConstShared.h"
+#include "BitcastBuffer.h"
 #include "Boolean.h"
 #include "DynamicAllocator.h"
 #include "FixedPoint.h"
@@ -3050,24 +3051,24 @@ inline bool BitCast(InterpState &S, CodePtr OpPC, bool TargetIsUCharOrByte,
   llvm::SmallVector<std::byte> Buff(BuffSize);
   bool HasIndeterminateBits = false;
 
-  if (!DoBitCast(S, OpPC, FromPtr, Buff.data(), BuffSize, HasIndeterminateBits))
+  Bits FullBitWidth(ResultBitWidth);
+  Bits BitWidth = FullBitWidth;
+
+  if constexpr (std::is_same_v<T, Floating>) {
+    assert(Sem);
+    BitWidth = Bits(llvm::APFloatBase::getSizeInBits(*Sem));
+  }
+
+  if (!DoBitCast(S, OpPC, FromPtr, Buff.data(), BitWidth, FullBitWidth,
+                 HasIndeterminateBits))
     return false;
 
   if (!CheckBitCast(S, OpPC, HasIndeterminateBits, TargetIsUCharOrByte))
     return false;
 
   if constexpr (std::is_same_v<T, Floating>) {
     assert(Sem);
-    ptrdiff_t Offset = 0;
-
-    if (llvm::sys::IsBigEndianHost) {
-      unsigned NumBits = llvm::APFloatBase::getSizeInBits(*Sem);
-      assert(NumBits % 8 == 0);
-      assert(NumBits <= ResultBitWidth);
-      Offset = (ResultBitWidth - NumBits) / 8;
-    }
-
-    S.Stk.push<Floating>(T::bitcastFromMemory(Buff.data() + Offset, *Sem));
+    S.Stk.push<Floating>(T::bitcastFromMemory(Buff.data(), *Sem));
   } else {
     assert(!Sem);
     S.Stk.push<T>(T::bitcastFromMemory(Buff.data(), ResultBitWidth));

clang/lib/AST/ByteCode/InterpBuiltinBitCast.cpp

@@ -278,44 +278,49 @@ static bool readPointerToBuffer(const Context &Ctx, const Pointer &FromPtr,
           if (llvm::sys::IsBigEndianHost)
             swapBytes(Buff.get(), NumBits.roundToBytes());
 
+          Buffer.markInitialized(BitOffset, NumBits);
         } else {
           BITCAST_TYPE_SWITCH(T, { P.deref<T>().bitcastToMemory(Buff.get()); });
 
           if (llvm::sys::IsBigEndianHost)
             swapBytes(Buff.get(), FullBitWidth.roundToBytes());
+          Buffer.markInitialized(BitOffset, BitWidth);
         }
 
         Buffer.pushData(Buff.get(), BitOffset, BitWidth, TargetEndianness);
-        Buffer.markInitialized(BitOffset, BitWidth);
         return true;
       });
 }
 
 bool clang::interp::DoBitCast(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
-                              std::byte *Buff, size_t BuffSize,
+                              std::byte *Buff, Bits BitWidth, Bits FullBitWidth,
                               bool &HasIndeterminateBits) {
   assert(Ptr.isLive());
   assert(Ptr.isBlockPointer());
   assert(Buff);
+  assert(BitWidth <= FullBitWidth);
+  assert(FullBitWidth.isFullByte());
+  assert(BitWidth.isFullByte());
 
-  Bits BitSize = Bytes(BuffSize).toBits();
-  BitcastBuffer Buffer(BitSize);
+  BitcastBuffer Buffer(FullBitWidth);
+  size_t BuffSize = FullBitWidth.roundToBytes();
   if (!CheckBitcastType(S, OpPC, Ptr.getType(), /*IsToType=*/false))
     return false;
 
   bool Success = readPointerToBuffer(S.getContext(), Ptr, Buffer,
                                      /*ReturnOnUninit=*/false);
-  HasIndeterminateBits = !Buffer.allInitialized();
+  HasIndeterminateBits = !Buffer.rangeInitialized(Bits::zero(), BitWidth);
 
   const ASTContext &ASTCtx = S.getASTContext();
   Endian TargetEndianness =
       ASTCtx.getTargetInfo().isLittleEndian() ? Endian::Little : Endian::Big;
-  auto B = Buffer.copyBits(Bits::zero(), BitSize, BitSize, TargetEndianness);
+  auto B =
+      Buffer.copyBits(Bits::zero(), BitWidth, FullBitWidth, TargetEndianness);
 
   std::memcpy(Buff, B.get(), BuffSize);
 
   if (llvm::sys::IsBigEndianHost)
-    swapBytes(Buff, BuffSize);
+    swapBytes(Buff, BitWidth.roundToBytes());
 
   return Success;
 }

clang/lib/AST/ByteCode/InterpBuiltinBitCast.h

@@ -9,6 +9,7 @@
 #ifndef LLVM_CLANG_AST_INTERP_BUILITN_BIT_CAST_H
 #define LLVM_CLANG_AST_INTERP_BUILITN_BIT_CAST_H
 
+#include "BitcastBuffer.h"
 #include <cstddef>
 
 namespace clang {
@@ -18,7 +19,8 @@ class InterpState;
 class CodePtr;
 
 bool DoBitCast(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
-               std::byte *Buff, size_t BuffSize, bool &HasIndeterminateBits);
+               std::byte *Buff, Bits BitWidth, Bits FullBitWidth,
+               bool &HasIndeterminateBits);
 bool DoBitCastPtr(InterpState &S, CodePtr OpPC, const Pointer &FromPtr,
                   Pointer &ToPtr);
 bool DoBitCastPtr(InterpState &S, CodePtr OpPC, const Pointer &FromPtr,

clang/test/AST/ByteCode/builtin-bit-cast-long-double.cpp

@@ -6,7 +6,10 @@
 // RUN: %clang_cc1 -verify=expected,both -std=c++2a -fsyntax-only -triple x86_64-apple-macosx10.14.0 %s -fno-signed-char -fexperimental-new-constant-interpreter
 // RUN: %clang_cc1 -verify=expected,both -std=c++2a -fsyntax-only -triple aarch64_be-linux-gnu %s -fexperimental-new-constant-interpreter
 
+#if !__x86_64
 // both-no-diagnostics
+#endif
+
 
 typedef decltype(nullptr) nullptr_t;
 typedef __INTPTR_TYPE__ intptr_t;
@@ -35,6 +38,7 @@ constexpr Init round_trip(const Init &init) {
 
 namespace test_long_double {
 #if __x86_64
+/// FIXME: We could enable this, but since it aborts, it causes the usual mempory leak.
 #if 0
 constexpr __int128_t test_cast_to_int128 = bit_cast<__int128_t>((long double)0); // expected-error{{must be initialized by a constant expression}}\
                                                                                  // expected-note{{in call}}
@@ -49,7 +53,13 @@ static_assert(round_trip<bytes>(ld), "");
 
 static_assert(round_trip<long double>(10.0L));
 
-#if 0
+constexpr long double foo() {
+  bytes A = __builtin_bit_cast(bytes, ld);
+  long double ld = __builtin_bit_cast(long double, A);
+  return ld;
+}
+static_assert(foo() == ld);
+
 constexpr bool f(bool read_uninit) {
   bytes b = bit_cast<bytes>(ld);
   unsigned char ld_bytes[10] = {
@@ -61,16 +71,15 @@ constexpr bool f(bool read_uninit) {
     if (ld_bytes[i] != b.d[i])
       return false;
 
-  if (read_uninit && b.d[10]) // expected-note{{read of uninitialized object is not allowed in a constant expression}}
+  if (read_uninit && b.d[10]) // both-note{{read of uninitialized object is not allowed in a constant expression}}
     return false;
 
   return true;
 }
 
 static_assert(f(/*read_uninit=*/false), "");
-static_assert(f(/*read_uninit=*/true), ""); // expected-error{{static assertion expression is not an integral constant expression}} \
-                                            // expected-note{{in call to 'f(true)'}}
-#endif
+static_assert(f(/*read_uninit=*/true), ""); // both-error{{static assertion expression is not an integral constant expression}} \
+                                            // both-note{{in call to 'f(true)'}}
 constexpr bytes ld539 = {
   0x0, 0x0,  0x0,  0x0,
   0x0, 0x0,  0xc0, 0x86,