Define __FLT_EVAL_METHOD__ when input source is stdin.

[zahiraam]

Summary

When the input source is stdin, the FLT_EVAL_METHOD macro is not set.
This patch defines it.

[aaron.ballman]

clang/lib/Frontend/FrontendAction.cpp

845–855

I'm confused as to why we want to predefine this macro *only* when the input source is stdin? So I'm not certain I understand why this change is desired.

e.g., https://godbolt.org/z/E8Y67381r (note how there's no __FLT_EVAL_METHOD__ defined there)

[zahiraam]

clang/lib/Frontend/FrontendAction.cpp

845–855

I was offering a solution to the issue raised by @glandium in https://reviews.llvm.org/D109239. I thought that the issue was only when the source is stdin, but obviously not. The default setting should happen under no condition.

[aaron.ballman]

clang/lib/Frontend/FrontendAction.cpp

845–855

There have been a lot of reviews over this stuff, so I may be remembering incorrectly... but I thought it was a conscious decision to *not* predefine __FLT_EVAL_METHOD__ because that value changes depending on pragmas in the TU. I thought the way that macro worked was that we registered it as a macro and we figure out its value at expansion time.

(The original report confused me into thinking that __FLT_EVAL_METHOD__ was behaving as though it was never defined, so expansion would never result in a correct value except when the eval method is 0.)

[zahiraam]

clang/lib/Frontend/FrontendAction.cpp

845–855

Yes, you are remembering correctly. I looked at older comments and it's something that was intended. We didn't want to pre-define it, until it is set at expansion.

[aaron.ballman]

clang/lib/Frontend/FrontendAction.cpp

845–855

Thank you for double-checking! I would recommend that you abandon this change, and instead make an NFC change to https://clang.llvm.org/docs/UsersManual.html#a-note-about-flt-eval-method to make it clear that this macro does not appear when dumping preprocessor macro definitions but is instead resolved when expanding it as a macro definition.

[zahiraam]

clang/lib/Frontend/FrontendAction.cpp

845–855

Good idea! I seem to be regularly falling into forgetting this.

clang/lib/Frontend/FrontendAction.cpp

 //===--- FrontendAction.cpp -----------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "clang/Frontend/FrontendAction.h"
 #include "clang/AST/ASTConsumer.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/DeclGroup.h"
 #include "clang/Basic/Builtins.h"
 #include "clang/Basic/LangStandard.h"
+#include "clang/Basic/MacroBuilder.h"
 #include "clang/Frontend/ASTUnit.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/FrontendDiagnostic.h"
 #include "clang/Frontend/FrontendPluginRegistry.h"
 #include "clang/Frontend/LayoutOverrideSource.h"
 #include "clang/Frontend/MultiplexConsumer.h"
 #include "clang/Frontend/Utils.h"
 #include "clang/Lex/HeaderSearch.h"
if (CI.getLangOpts().CPlusPlusModules && Input.getKind().isHeaderUnit() &&
     }
     // Unless the user has overridden the name, the header unit module name is
     // the pathname for the file.
     if (CI.getLangOpts().ModuleName.empty())
       CI.getLangOpts().ModuleName = std::string(FileName);
     CI.getLangOpts().CurrentModule = CI.getLangOpts().ModuleName;
   }
 
+  // Set the __FLT_EVAL_METHOD__ when the input source is stdin.
+  if (Input.isFile() && Input.getFile() == "-") {
+    Preprocessor &PP = CI.getPreprocessor();
+    std::string PredefineBuffer;
+    PredefineBuffer.reserve(4080);
+    llvm::raw_string_ostream Predefines(PredefineBuffer);
+    Predefines << PP.getPredefines();
+    MacroBuilder Builder(Predefines);
+    Builder.append("# 1 \"<built-in>\" 3");
+    Builder.defineMacro("__FLT_EVAL_METHOD__", Twine(PP.getTUFPEvalMethod()));
+    PP.setPredefines(Predefines.str());
+  }
+
   if (!CI.InitializeSourceManager(Input))
     return false;
 
   if (CI.getLangOpts().CPlusPlusModules && Input.getKind().isHeaderUnit() &&
       Input.getKind().isPreprocessed() && !usesPreprocessorOnly()) {
     // We have an input filename like foo.iih, but we want to find the right
     // module name (and original file, to build the map entry).
     // Check if the first line specifies the original source file name with a

clang/test/Preprocessor/flt_eval_macro.cpp

 
 // RUN: %clang_cc1 -E -dM -triple i386-pc-windows -target-cpu pentium4 %s -o - \
 // RUN:   | FileCheck %s  -strict-whitespace
 
 // RUN: %clang_cc1 -E -dM -triple i386-pc-windows -target-cpu pentium4 \
 // RUN:   -target-feature -sse %s -o - | FileCheck -check-prefix=EXT %s \
 // RUN:   -strict-whitespace
 
+// RUN: %clang_cc1 -E -dM -triple=x86_64-none-none  < /dev/null \
+// RUN:   | FileCheck %s  --check-prefix=CHECK-FEM
+
+// RUN: %clang_cc1 -E -dM -triple=x86_64-none-none -target-feature -sse \
+// RUN:   < /dev/null | FileCheck %s  --check-prefix=CHECK-FEM-EXT
+
+// RUN: %clang_cc1 -E -dM -triple=arm64e-apple-ios -target-feature -sse \
+// RUN:   < /dev/null | FileCheck %s  --check-prefix=CHECK-FEM
+
+// RUN: %clang_cc1 -E -dM -triple=arm64e-apple-ios -target-feature +sse \
+// RUN:   < /dev/null | FileCheck %s  --check-prefix=CHECK-FEM
+
+// RUN: %clang_cc1 -E -dM -triple=arm64_32-apple-ios < /dev/null \
+// RUN:   | FileCheck %s  --check-prefix=CHECK-FEM
+
+// RUN: %clang_cc1 -E -dM -triple=arm64_32-apple-ios -target-feature -sse \
+// RUN:   < /dev/null | FileCheck %s  --check-prefix=CHECK-FEM
+
+// RUN: %clang_cc1 -E -dM -triple i386-pc-windows -target-cpu pentium4 \
+// RUN:   < /dev/null | FileCheck %s  --check-prefix=CHECK-FEM
+
+// RUN: %clang_cc1 -E -dM -triple i386-pc-windows -target-cpu pentium4 \
+// RUN:   -target-feature -sse < /dev/null \
+// RUN:   | FileCheck %s  --check-prefix=CHECK-FEM-EXT
+
 #ifdef __FLT_EVAL_METHOD__
 #if __FLT_EVAL_METHOD__ == 3
 #define __GLIBC_FLT_EVAL_METHOD 2
 #else
 #define __GLIBC_FLT_EVAL_METHOD __FLT_EVAL_METHOD__
 #endif
 #elif defined __x86_64__
 #define __GLIBC_FLT_EVAL_METHOD 0

 #define Val "val2"
 #endif
 
 int goo() {
   // CHECK: #define Val "val0"
   // EXT: #define Val "val2"
   return Val;
 }
+
+// CHECK-FEM: #define __FLT_EVAL_METHOD__ 0
+// CHECK-FEM-EXT: #define __FLT_EVAL_METHOD__ 2

clang/test/Preprocessor/init.c

 // WEBASSEMBLY-NOT:#define __FLT16_MAX__
 // WEBASSEMBLY-NOT:#define __FLT16_MIN_10_EXP__
 // WEBASSEMBLY-NOT:#define __FLT16_MIN_EXP__
 // WEBASSEMBLY-NOT:#define __FLT16_MIN__
 // WEBASSEMBLY-NEXT:#define __FLT_DECIMAL_DIG__ 9
 // WEBASSEMBLY-NEXT:#define __FLT_DENORM_MIN__ 1.40129846e-45F
 // WEBASSEMBLY-NEXT:#define __FLT_DIG__ 6
 // WEBASSEMBLY-NEXT:#define __FLT_EPSILON__ 1.19209290e-7F
+// WEBASSEMBLY-NEXT:#define __FLT_EVAL_METHOD__ 0
 // WEBASSEMBLY-NEXT:#define __FLT_HAS_DENORM__ 1
 // WEBASSEMBLY-NEXT:#define __FLT_HAS_INFINITY__ 1
 // WEBASSEMBLY-NEXT:#define __FLT_HAS_QUIET_NAN__ 1
 // WEBASSEMBLY-NEXT:#define __FLT_MANT_DIG__ 24
 // WEBASSEMBLY-NEXT:#define __FLT_MAX_10_EXP__ 38
 // WEBASSEMBLY-NEXT:#define __FLT_MAX_EXP__ 128
 // WEBASSEMBLY-NEXT:#define __FLT_MAX__ 3.40282347e+38F
 // WEBASSEMBLY-NEXT:#define __FLT_MIN_10_EXP__ (-37)