[DebugInfo] Add support for __fp16, float, and double constants.

[dgross]

Summary

Partial fix for PR26619.

Prior to this change, a DIGlobalVariable corresponding to a static
const was marked with an expression corresponding to its constant
value only if it is of integral type. With this change, we now do the
same if it is of __fp16, float, or double type (that is,
floating-point types that do not exceed 64 bits in size, and hence are
supported easily by the existing LLVM machinery for creating constant
expressions in debug info).

[dgross]

See llvm regression test here: https://reviews.llvm.org/D27551

[probinson]

Hi David!
As this is a Clang patch, you should subscribe cfe-commits rather than llvm-commits. I've done that for you.
See also inline comments.

lib/CodeGen/CGDebugInfo.cpp

3765 ↗

(On Diff #80674)

This line exceeds 80 columns. clang-format is your friend.

test/CodeGen/debug-info-static-const-fp.c

19 ↗

(On Diff #80674)

Checking for the entire exact line for the variable is a bit fragile. Really what you want to do is associate the variable with the correct expression, and ignore all the irrelevant details. Something like this:

// CHECK: DIGlobalVariable(name: "hVal", {{.*}} expr: ![[HEXPR:{{[0-9]+}}]]
// CHECK: ![[HEXPR] = ! DIExpression(DW_OP_constu, 16502, DW_OP_stack_value)

And similar pairs for the other variables. I'd use a different FileCheck variable for each case.

[dgross]

Incorporate code review feedback.

• Reformat source.
• Make test pattern more general.

[dgross]

lib/CodeGen/CGDebugInfo.cpp

3765 ↗

(On Diff #80674)

Done. Is clang-format mentioned in any of the documentation that describes the development process? I might have missed it (not that that's an excuse for a needless violation of the coding guidelines).

test/CodeGen/debug-info-static-const-fp.c

19 ↗

(On Diff #80674)

Thanks for the suggestion. I didn't realize FileCheck had variable support.

[probinson]

LGTM.

lib/CodeGen/CGDebugInfo.cpp

3765 ↗

(On Diff #80674)

I would have thought the coding guidelines would mention clang-format, but I'm not finding it there (or in the stuff about submitting a patch).

cfe/trunk/lib/CodeGen/CGDebugInfo.cpp

void CGDebugInfo::EmitGlobalVariable(const ValueDecl *VD, const APValue &Init) {
 
   auto &GV = DeclCache[VD];
   if (GV)
     return;
   llvm::DIExpression *InitExpr = nullptr;
   if (Init.isInt())
     InitExpr =
         DBuilder.createConstantValueExpression(Init.getInt().getExtValue());
+  else if (Init.isFloat() && CGM.getContext().getTypeSize(VD->getType()) <= 64)
+    InitExpr = DBuilder.createConstantValueExpression(
+        Init.getFloat().bitcastToAPInt().getZExtValue());
   GV.reset(DBuilder.createGlobalVariable(
       DContext, Name, StringRef(), Unit, getLineNumber(VD->getLocation()), Ty,
       true, InitExpr, getOrCreateStaticDataMemberDeclarationOrNull(VarD),
       Align));
 }
 
 llvm::DIScope *CGDebugInfo::getCurrentContextDescriptor(const Decl *D) {
   if (!LexicalBlockStack.empty())

cfe/trunk/test/CodeGen/debug-info-static-const-fp.c

+// RUN: %clang -emit-llvm -O0 -S -g %s -o - | FileCheck %s
+
+// Per PR26619, check that for referenced static const of floating-point type,
+// we emit its constant value in debug info.  NOTE that PR26619 is not yet fixed for long double.
+
+static const __fp16 hVal = 29/13.0f;            //    2.2307692307692307692     (2.23046875)
+
+static const float fVal = -147/17.0f;           //   -8.6470588235294117647     (-8.64705849)
+
+static const double dVal = 19637/7.0;           // 2805.2857142857142857        (2805.2857142857142)
+
+static const long double ldVal = 3/1234567.0L;  //    2.4300017739012949479e-06 (<optimized out>)
+
+int main() {
+  return hVal + fVal + dVal + ldVal;
+}
+
+// CHECK: !DIGlobalVariable(name: "hVal", {{.*}}, isLocal: true, isDefinition: true, expr: ![[HEXPR:[0-9]+]]
+// CHECK: ![[HEXPR]] = !DIExpression(DW_OP_constu, 16502, DW_OP_stack_value)
+
+// CHECK: !DIGlobalVariable(name: "fVal", {{.*}}, isLocal: true, isDefinition: true, expr: ![[FEXPR:[0-9]+]]
+// CHECK: ![[FEXPR]] = !DIExpression(DW_OP_constu, 3238681178, DW_OP_stack_value)
+
+// CHECK: !DIGlobalVariable(name: "dVal", {{.*}}, isLocal: true, isDefinition: true, expr: ![[DEXPR:[0-9]+]]
+// CHECK: ![[DEXPR]] = !DIExpression(DW_OP_constu, 4658387303597904457, DW_OP_stack_value)
+
+// CHECK: !DIGlobalVariable(name: "ldVal", {{.*}}, isLocal: true, isDefinition: true)