[clang] Add `__bf16` Type Support Macros With Literal Suffix Support #134214

bassiounix · 2025-04-03T08:13:47Z

I added the suffix support to this pr as the generated macros uses the BF16 suffix.

The only line I found in GCC which we don't seem to support as a macro is

#define __BFLT16_IS_IEC_60559__ 0

we don't have __*_IS_IEC_60559__ in our macro builder so I skipped it.

cc @AaronBallman @lntue @jhuber6

llvmbot · 2025-04-03T08:14:23Z

@llvm/pr-subscribers-clang

Author: Muhammad Bassiouni (bassiounix)

Changes

closes #133660.

I added the suffix support to this pr as the generated macros uses the BF16 suffix.

The only line I found in GCC which we don't seem to support as a macro is

#define __BFLT16_IS_IEC_60559__ 0

we don't have __*_IS_IEC_60559__ in our macro builder so I skipped it.

cc @AaronBallman @lntue @jhuber6

Full diff: https://github.com/llvm/llvm-project/pull/134214.diff

4 Files Affected:

(modified) clang/include/clang/Lex/LiteralSupport.h (+1)
(modified) clang/lib/Frontend/InitPreprocessor.cpp (+17-8)
(modified) clang/lib/Lex/LiteralSupport.cpp (+16-1)
(modified) clang/lib/Sema/SemaExpr.cpp (+2)

diff --git a/clang/include/clang/Lex/LiteralSupport.h b/clang/include/clang/Lex/LiteralSupport.h
index ea5f63bc20399..1907cfc365d97 100644
--- a/clang/include/clang/Lex/LiteralSupport.h
+++ b/clang/include/clang/Lex/LiteralSupport.h
@@ -77,6 +77,7 @@ class NumericLiteralParser {
   bool isFloat : 1;         // 1.0f
   bool isImaginary : 1;     // 1.0i
   bool isFloat16 : 1;       // 1.0f16
+  bool isBFloat16 : 1;      // 1.0bf16
   bool isFloat128 : 1;      // 1.0q
   bool isFract : 1;         // 1.0hr/r/lr/uhr/ur/ulr
   bool isAccum : 1;         // 1.0hk/k/lk/uhk/uk/ulk
diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 0b54665501c76..9bca74a8b4bd6 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -96,7 +96,7 @@ static void AddImplicitIncludePCH(MacroBuilder &Builder, Preprocessor &PP,
 template <typename T>
 static T PickFP(const llvm::fltSemantics *Sem, T IEEEHalfVal, T IEEESingleVal,
                 T IEEEDoubleVal, T X87DoubleExtendedVal, T PPCDoubleDoubleVal,
-                T IEEEQuadVal) {
+                T BFloatVal, T IEEEQuadVal) {
   if (Sem == (const llvm::fltSemantics*)&llvm::APFloat::IEEEhalf())
     return IEEEHalfVal;
   if (Sem == (const llvm::fltSemantics*)&llvm::APFloat::IEEEsingle())
@@ -107,6 +107,8 @@ static T PickFP(const llvm::fltSemantics *Sem, T IEEEHalfVal, T IEEESingleVal,
     return X87DoubleExtendedVal;
   if (Sem == (const llvm::fltSemantics*)&llvm::APFloat::PPCDoubleDouble())
     return PPCDoubleDoubleVal;
+  if (Sem == (const llvm::fltSemantics*)&llvm::APFloat::BFloat())
+    return BFloatVal;
   assert(Sem == (const llvm::fltSemantics*)&llvm::APFloat::IEEEquad());
   return IEEEQuadVal;
 }
@@ -117,29 +119,34 @@ static void DefineFloatMacros(MacroBuilder &Builder, StringRef Prefix,
   NormMax = PickFP(Sem, "6.5504e+4", "3.40282347e+38",
                    "1.7976931348623157e+308", "1.18973149535723176502e+4932",
                    "8.98846567431157953864652595394501e+307",
+                   "3.38953138925153547590470800371487867e+38",
                    "1.18973149535723176508575932662800702e+4932");
   DenormMin = PickFP(Sem, "5.9604644775390625e-8", "1.40129846e-45",
                      "4.9406564584124654e-324", "3.64519953188247460253e-4951",
                      "4.94065645841246544176568792868221e-324",
+                     "9.18354961579912115600575419704879436e-41",
                      "6.47517511943802511092443895822764655e-4966");
-  int Digits = PickFP(Sem, 3, 6, 15, 18, 31, 33);
-  int DecimalDigits = PickFP(Sem, 5, 9, 17, 21, 33, 36);
+  int Digits = PickFP(Sem, 3, 6, 15, 18, 31, 2, 33);
+  int DecimalDigits = PickFP(Sem, 5, 9, 17, 21, 33, 4, 36);
   Epsilon = PickFP(Sem, "9.765625e-4", "1.19209290e-7",
                    "2.2204460492503131e-16", "1.08420217248550443401e-19",
                    "4.94065645841246544176568792868221e-324",
+                   "7.81250000000000000000000000000000000e-3",
                    "1.92592994438723585305597794258492732e-34");
-  int MantissaDigits = PickFP(Sem, 11, 24, 53, 64, 106, 113);
-  int Min10Exp = PickFP(Sem, -4, -37, -307, -4931, -291, -4931);
-  int Max10Exp = PickFP(Sem, 4, 38, 308, 4932, 308, 4932);
-  int MinExp = PickFP(Sem, -13, -125, -1021, -16381, -968, -16381);
-  int MaxExp = PickFP(Sem, 16, 128, 1024, 16384, 1024, 16384);
+  int MantissaDigits = PickFP(Sem, 11, 24, 53, 64, 106, 8, 113);
+  int Min10Exp = PickFP(Sem, -4, -37, -307, -4931, -291, -37, -4931);
+  int Max10Exp = PickFP(Sem, 4, 38, 308, 4932, 308, 38, 4932);
+  int MinExp = PickFP(Sem, -13, -125, -1021, -16381, -968, -125, -16381);
+  int MaxExp = PickFP(Sem, 16, 128, 1024, 16384, 1024, 128, 16384);
   Min = PickFP(Sem, "6.103515625e-5", "1.17549435e-38", "2.2250738585072014e-308",
                "3.36210314311209350626e-4932",
                "2.00416836000897277799610805135016e-292",
+               "1.17549435082228750796873653722224568e-38",
                "3.36210314311209350626267781732175260e-4932");
   Max = PickFP(Sem, "6.5504e+4", "3.40282347e+38", "1.7976931348623157e+308",
                "1.18973149535723176502e+4932",
                "1.79769313486231580793728971405301e+308",
+               "3.38953138925153547590470800371487867e+38",
                "1.18973149535723176508575932662800702e+4932");
 
   SmallString<32> DefPrefix;
@@ -1250,6 +1257,8 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
 
   if (TI.hasFloat16Type())
     DefineFloatMacros(Builder, "FLT16", &TI.getHalfFormat(), "F16");
+  if (TI.hasBFloat16Type())
+    DefineFloatMacros(Builder, "BFLT16", &TI.getBFloat16Format(), "BF16");
   DefineFloatMacros(Builder, "FLT", &TI.getFloatFormat(), "F");
   DefineFloatMacros(Builder, "DBL", &TI.getDoubleFormat(), "");
   DefineFloatMacros(Builder, "LDBL", &TI.getLongDoubleFormat(), "L");
diff --git a/clang/lib/Lex/LiteralSupport.cpp b/clang/lib/Lex/LiteralSupport.cpp
index 20933cc8dee69..ab0d301a70fbd 100644
--- a/clang/lib/Lex/LiteralSupport.cpp
+++ b/clang/lib/Lex/LiteralSupport.cpp
@@ -917,6 +917,7 @@ NumericLiteralParser::NumericLiteralParser(StringRef TokSpelling,
   isFloat = false;
   isImaginary = false;
   isFloat16 = false;
+  isBFloat16 = false;
   isFloat128 = false;
   MicrosoftInteger = 0;
   isFract = false;
@@ -973,11 +974,20 @@ NumericLiteralParser::NumericLiteralParser(StringRef TokSpelling,
   bool isFPConstant = isFloatingLiteral();
   bool HasSize = false;
   bool DoubleUnderscore = false;
+  bool isBF16 = false;
 
   // Loop over all of the characters of the suffix.  If we see something bad,
   // we break out of the loop.
   for (; s != ThisTokEnd; ++s) {
     switch (*s) {
+    case 'b':
+    case 'B':
+      if (isBFloat16) break;
+      if (isBF16) break;
+      if (HasSize) break;
+
+      isBF16 = true;
+      continue;
     case 'R':
     case 'r':
       if (!LangOpts.FixedPoint)
@@ -1022,7 +1032,11 @@ NumericLiteralParser::NumericLiteralParser(StringRef TokSpelling,
            (LangOpts.OpenMPIsTargetDevice && Target.getTriple().isNVPTX())) &&
           s + 2 < ThisTokEnd && s[1] == '1' && s[2] == '6') {
         s += 2; // success, eat up 2 characters.
-        isFloat16 = true;
+        if (isBF16) {
+          isBFloat16 = true;
+        } else {
+          isFloat16 = true;
+        }
         continue;
       }
 
@@ -1183,6 +1197,7 @@ NumericLiteralParser::NumericLiteralParser(StringRef TokSpelling,
         isSizeT = false;
         isFloat = false;
         isFloat16 = false;
+        isBFloat16 = false;
         isHalf = false;
         isImaginary = false;
         isBitInt = false;
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 3af6d6c23438f..b4210fc22ae52 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -3878,6 +3878,8 @@ ExprResult Sema::ActOnNumericConstant(const Token &Tok, Scope *UDLScope) {
       Ty = !getLangOpts().HLSL ? Context.LongDoubleTy : Context.DoubleTy;
     else if (Literal.isFloat16)
       Ty = Context.Float16Ty;
+    else if (Literal.isBFloat16)
+      Ty = Context.BFloat16Ty;
     else if (Literal.isFloat128)
       Ty = Context.Float128Ty;
     else if (getLangOpts().HLSL)

github-actions · 2025-04-03T08:16:12Z

✅ With the latest revision this PR passed the C/C++ code formatter.

bassiounix · 2025-04-03T10:04:49Z

I changed the commits and ran test at each step,
I'm not sure why the last commit made the test failing!
is APFloat::BFloat the reason? if so, how would I set the value?

AaronBallman

Thank you for this! It's heading in the right direction. Some things which are still missing are;

a release note in clang/docs/ReleaseNotes.rst so users know about the new suffix and macros.
test coverage
- clang/test/Lexer/ should get a test for the literal suffix support
- clang/test/Preprocessor/ should get a test for the new predefined macros

As for the current test failures, they're both hitting the same failed assertion:

clang: /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-bt7k7-1/llvm-project/github-pull-requests/clang/lib/Frontend/InitPreprocessor.cpp:112: T PickFP(const llvm::fltSemantics *, T, T, T, T, T, T, T) [T = const char *]: Assertion `Sem == (const llvm::fltSemantics*)&llvm::APFloat::IEEEquad()' failed.

It almost seems as though &TI.getBFloat16Format() is returning something other than &llvm::APFloat::BFloat() for a target and thus it falls into the quad assertion while not being a quad semantics. You'll likely have to hook up a debugger to see what's going on there.

clang/lib/Frontend/InitPreprocessor.cpp

overmighty

This PR currently adds two suffixes: bf16 and just b. Is this intended? GCC seems to only support bf16: https://godbolt.org/z/hEfcrGrG1.

It currently also lets Clang accept the following C++ code if the target doesn't have bfloat16 but has float16:

auto foo = 1.0bf16;

And it lets Clang accept the following C++ code even if the target has neither bfloat16 nor float16:

auto foo = 1.0b;

It also looks like foo ends up being of type double either way (edit: nevermind, it was only happening with 1.0b, because it was only setting the isBF16 local variable and not isBFloat16):

TranslationUnitDecl 0x5f0373f42d48 <<invalid sloc>> <invalid sloc>
|-TypedefDecl 0x5f0373f439d0 <<invalid sloc>> <invalid sloc> implicit __int128_t '__int128'
| `-BuiltinType 0x5f0373f43310 '__int128'
|-TypedefDecl 0x5f0373f43a40 <<invalid sloc>> <invalid sloc> implicit __uint128_t 'unsigned __int128'
| `-BuiltinType 0x5f0373f43330 'unsigned __int128'
|-TypedefDecl 0x5f0373f91f70 <<invalid sloc>> <invalid sloc> implicit __NSConstantString '__NSConstantString_tag'
| `-RecordType 0x5f0373f43b30 '__NSConstantString_tag'
|   `-CXXRecord 0x5f0373f43a98 '__NSConstantString_tag'
|-TypedefDecl 0x5f0373f43608 <<invalid sloc>> <invalid sloc> implicit __builtin_ms_va_list 'char *'
| `-PointerType 0x5f0373f435c0 'char *'
|   `-BuiltinType 0x5f0373f42df0 'char'
|-TypedefDecl 0x5f0373f43960 <<invalid sloc>> <invalid sloc> implicit __builtin_va_list '__va_list_tag[1]'
| `-ConstantArrayType 0x5f0373f43910 '__va_list_tag[1]' 1
|   `-RecordType 0x5f0373f436f0 '__va_list_tag'
|     `-CXXRecord 0x5f0373f43660 '__va_list_tag'
`-VarDecl 0x5f0373f92018 <a.cpp:1:1, col:12> col:6 foo 'double' cinit
  `-FloatingLiteral 0x5f0373f920c8 <col:12> 'double' 1.000000e+00

clang/lib/Frontend/InitPreprocessor.cpp

clang/lib/Lex/LiteralSupport.cpp

bassiounix · 2025-04-04T07:25:52Z

Looks like that BFloat16Format for amdgcn-amd-amdhsa target is not properly initialized and the hasBFloat16Type method at clang/lib/Basic/Targets/AMDGPU.h is using a dummy check to that is based on the triple value only. Also there's no overrides for a full type support.

The global value of BFloat16Format in AMDGPUTI is properly initialized.

I think TargetInfo::adjust at clang/lib/Basic/TargetInfo.cpp may be the reason but I'm not sure

Edit: was just a "copy" problem

clang/lib/Lex/LiteralSupport.cpp

clang/test/Lexer/bfloat-literal.cpp

Co-authored-by: OverMighty <[email protected]>

clang/lib/Lex/LiteralSupport.cpp

cor3ntin · 2025-04-07T10:11:32Z

clang/lib/Lex/LiteralSupport.cpp

+    case 'b': // FP Suffix for "__bf16"
+    case 'B':
+      if (!Target.hasBFloat16Type())
+        break;
+      if (!isFPConstant)
+        break; // Error for integer constant.
+      if (HasSize)
+        break;
+      HasSize = true;
+
+      if (s + 3 < ThisTokEnd &&
+          ((s[0] == 'b' && s[1] == 'f') || (s[0] == 'B' && s[1] == 'F')) &&
+          s[2] == '1' && s[3] == '6') {
+        s += 3; // success, eat up 3 characters.
+        isBFloat16 = true;
+        continue;
+      }
+      break;


This is true for C++23. Do we want extension warnings in other language modes @AaronBallman?

As an aside, did anyone benchmark that the pattern we use in this function is actually faster than string_view
comparisons?

Yes, we should have extension warnings in other language modes as well as the precompat warning for C++ before C++23.

bassiounix added 2 commits April 3, 2025 10:08

add bf16/BF16 suffix support

620bdbe

add __bf16 macros

d55e0ca

llvmbot added clang Clang issues not falling into any other category clang:frontend Language frontend issues, e.g. anything involving "Sema" labels Apr 3, 2025

fix formatting

d0b9ecd

overmighty self-requested a review April 3, 2025 11:29

AaronBallman requested review from cor3ntin, AaronBallman, jhuber6 and lntue April 3, 2025 12:00

AaronBallman reviewed Apr 3, 2025

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bassiounix added 6 commits April 3, 2025 22:40

chore(style): fix redundant style

94244f4

chore: reorder PickFP arguments

5b25898

fix(bf suffix): fix float literal suffix support

2c62638

chore(docs): add release notes for the macros and bfloat literal suffix

3abe5e7

chore(test): add test for bfloat literal suffix support

9e48a49

chore(test): add test for __bf16/BFLT16 predefined macros

2680e73

bassiounix added 2 commits April 4, 2025 10:18

fix(TargetInfo): save state of the type format after copy

3b793b2

chore(style): fix code style

ae0cf84

bassiounix requested review from AaronBallman and overmighty April 4, 2025 08:31

overmighty reviewed Apr 4, 2025

View reviewed changes

bassiounix and others added 3 commits April 4, 2025 11:09

Update clang/lib/Lex/LiteralSupport.cpp

621d5a3

Co-authored-by: OverMighty <[email protected]>

Update clang/lib/Lex/LiteralSupport.cpp

f6a05c3

Co-authored-by: OverMighty <[email protected]>

Update clang/lib/Lex/LiteralSupport.cpp

c272219

Co-authored-by: OverMighty <[email protected]>

bassiounix added 2 commits April 4, 2025 11:18

remove reduntant checks

33d9adb

add more bf16 literal suffix tests

3cc63e9

overmighty reviewed Apr 4, 2025

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bassiounix force-pushed the bf16-support branch from 77193d4 to 5cbd898 Compare April 4, 2025 09:47

remove redundant check

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bassiounix force-pushed the bf16-support branch from 5cbd898 to e88f537 Compare April 4, 2025 09:54

Add tests for unsupported target

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bassiounix requested a review from overmighty April 4, 2025 19:33

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