[lldb] Always use APFloat for FP dumping

The DumpDataExtractor function had two branches for printing floating
point values. One branch (APFloat) was used if we had a Target object
around and could query it for the appropriate semantics. If we didn't
have a Target, we used host operations to read and format the value.

This patch changes second path to use APFloat as well. To make it work,
I pick reasonable defaults for different byte size. Notably, I did not
include x87 long double in that list (as it is ambibuous and
architecture-specific). This exposed a bug where we were printing
register values using the target-less branch, even though the registers
definitely belong to a target, and we had it available. Fixing this
prompted the update of several tests for register values due to slightly
different floating point outputs.

The most dubious aspect of this patch is the change in
TypeSystemClang::GetFloatTypeSemantics to recognize `10` as a valid size
for x87 long double. This was necessary because because sizeof(long
double) on x86_64 is 16 even though it only holds 10 bytes of useful
data. This generalizes the hackaround present in the target-free branch
of the dumping function.

Differential Revision: https://reviews.llvm.org/D129750

1 files changed, 50 insertions, 80 deletions

diff --git a/lldb/source/Core/DumpDataExtractor.cpp b/lldb/source/Core/DumpDataExtractor.cpp
index c48250b07d16..81544443eb85 100644
--- a/lldb/source/Core/DumpDataExtractor.cpp
+++ b/lldb/source/Core/DumpDataExtractor.cpp
@@ -50,25 +50,6 @@ using namespace lldb;
 
 #define NON_PRINTABLE_CHAR '.'
 
-static float half2float(uint16_t half) {
-  union {
-    float f;
-    uint32_t u;
-  } u;
-  // Sign extend to 4 byte.
-  int32_t sign_extended = static_cast<int16_t>(half);
-  uint32_t v = static_cast<uint32_t>(sign_extended);
-
-  if (0 == (v & 0x7c00)) {
-    u.u = v & 0x80007FFFU;
-    return u.f * ldexpf(1, 125);
-  }
-
-  v <<= 13;
-  u.u = v | 0x70000000U;
-  return u.f * ldexpf(1, -112);
-}
-
 static llvm::Optional<llvm::APInt> GetAPInt(const DataExtractor &data,
                                             lldb::offset_t *offset_ptr,
                                             lldb::offset_t byte_size) {
@@ -336,6 +317,27 @@ printMemoryTags(const DataExtractor &DE, Stream *s, lldb::addr_t addr,
   s->PutCString(")");
 }
 
+static const llvm::fltSemantics &GetFloatSemantics(const TargetSP &target_sp,
+                                                   size_t byte_size) {
+  if (target_sp) {
+    if (auto type_system_or_err =
+            target_sp->GetScratchTypeSystemForLanguage(eLanguageTypeC))
+      return type_system_or_err->GetFloatTypeSemantics(byte_size);
+    else
+      llvm::consumeError(type_system_or_err.takeError());
+  }
+  // No target, just make a reasonable guess
+  switch(byte_size) {
+    case 2:
+      return llvm::APFloat::IEEEhalf();
+    case 4:
+      return llvm::APFloat::IEEEsingle();
+    case 8:
+      return llvm::APFloat::IEEEdouble();
+  }
+  return llvm::APFloat::Bogus();
+}
+
 lldb::offset_t lldb_private::DumpDataExtractor(
     const DataExtractor &DE, Stream *s, offset_t start_offset,
     lldb::Format item_format, size_t item_byte_size, size_t item_count,
@@ -645,70 +647,38 @@ lldb::offset_t lldb_private::DumpDataExtractor(
 
     case eFormatFloat: {
       TargetSP target_sp;
-      bool used_upfloat = false;
       if (exe_scope)
         target_sp = exe_scope->CalculateTarget();
-      if (target_sp) {
-        auto type_system_or_err =
-            target_sp->GetScratchTypeSystemForLanguage(eLanguageTypeC);
-        if (!type_system_or_err) {
-          llvm::consumeError(type_system_or_err.takeError());
-        } else {
-          auto &type_system = *type_system_or_err;
-          llvm::SmallVector<char, 256> sv;
-          // Show full precision when printing float values
-          const unsigned format_precision = 0;
-          const unsigned format_max_padding =
-              target_sp->GetMaxZeroPaddingInFloatFormat();
-
-          const auto &semantics =
-              type_system.GetFloatTypeSemantics(item_byte_size);
-
-          // Recalculate the byte size in case of a difference. This is possible
-          // when item_byte_size is 16 (128-bit), because you could get back the
-          // x87DoubleExtended semantics which has a byte size of 10 (80-bit).
-          const size_t semantics_byte_size =
-              (llvm::APFloat::getSizeInBits(semantics) + 7) / 8;
-          llvm::Optional<llvm::APInt> apint =
-              GetAPInt(DE, &offset, semantics_byte_size);
-          if (apint) {
-            llvm::APFloat apfloat(semantics, apint.value());
-            apfloat.toString(sv, format_precision, format_max_padding);
-            if (!sv.empty()) {
-              s->Printf("%*.*s", (int)sv.size(), (int)sv.size(), sv.data());
-              used_upfloat = true;
-            }
-          }
-        }
-      }
 
-      if (!used_upfloat) {
-        std::ostringstream ss;
-        if (item_byte_size == sizeof(float) || item_byte_size == 2) {
-          float f;
-          if (item_byte_size == 2) {
-            uint16_t half = DE.GetU16(&offset);
-            f = half2float(half);
-          } else {
-            f = DE.GetFloat(&offset);
-          }
-          ss.precision(std::numeric_limits<float>::digits10);
-          DumpFloatingPoint(ss, f);
-        } else if (item_byte_size == sizeof(double)) {
-          ss.precision(std::numeric_limits<double>::digits10);
-          DumpFloatingPoint(ss, DE.GetDouble(&offset));
-        } else if (item_byte_size == sizeof(long double) ||
-                   item_byte_size == 10) {
-          ss.precision(std::numeric_limits<long double>::digits10);
-          DumpFloatingPoint(ss, DE.GetLongDouble(&offset));
-        } else {
-          s->Printf("error: unsupported byte size (%" PRIu64
-                    ") for float format",
-                    (uint64_t)item_byte_size);
-          return offset;
-        }
-        ss.flush();
-        s->Printf("%s", ss.str().c_str());
+      llvm::Optional<unsigned> format_max_padding;
+      if (target_sp)
+        format_max_padding = target_sp->GetMaxZeroPaddingInFloatFormat();
+
+      // Show full precision when printing float values
+      const unsigned format_precision = 0;
+
+      const llvm::fltSemantics &semantics =
+          GetFloatSemantics(target_sp, item_byte_size);
+
+      // Recalculate the byte size in case of a difference. This is possible
+      // when item_byte_size is 16 (128-bit), because you could get back the
+      // x87DoubleExtended semantics which has a byte size of 10 (80-bit).
+      const size_t semantics_byte_size =
+          (llvm::APFloat::getSizeInBits(semantics) + 7) / 8;
+      llvm::Optional<llvm::APInt> apint =
+          GetAPInt(DE, &offset, semantics_byte_size);
+      if (apint) {
+        llvm::APFloat apfloat(semantics, apint.value());
+        llvm::SmallVector<char, 256> sv;
+        if (format_max_padding)
+          apfloat.toString(sv, format_precision, *format_max_padding);
+        else
+          apfloat.toString(sv, format_precision);
+        s->AsRawOstream() << sv;
+      } else {
+        s->Format("error: unsupported byte size ({0}) for float format",
+                  item_byte_size);
+        return offset;
       }
     } break;