[clang] f6f625f - [clang] Do not clear FP pragma stack when instantiating functions (#70646)

[via cfe-commits]

Author: Serge Pavlov
Date: 2023-11-13T17:24:46+07:00
New Revision: f6f625f4c6c3cbeb8cf6b889cdafc848dd4cb117

URL: https://github.com/llvm/llvm-project/commit/f6f625f4c6c3cbeb8cf6b889cdafc848dd4cb117
DIFF: https://github.com/llvm/llvm-project/commit/f6f625f4c6c3cbeb8cf6b889cdafc848dd4cb117.diff

LOG: [clang] Do not clear FP pragma stack when instantiating functions (#70646)

When instantiation function, a call to Sema::resetFPOption was used to
set the FP options associated with AST node. However this function also
cleared FP pragma stack, and it is incorrect. Template instantiation
takes place on AST representation and semantic information like the FP
pragma stack should not affect it. This was a reason for miscompilation
in some cases.

To make the Sema interface more consistent, now `resetFPOptions` does
not clear FP pragma stack anymore. It is cleared in
`FpPragmaStackSaveRAII`, which is used in parsing only.

This change must fix https://github.com/llvm/llvm-project/issues/69717
(Problems with float_control pragma stack in Clang 17.x).

Added: 
    clang/test/Sema/PR69717.cpp

Modified: 
    clang/include/clang/Sema/Sema.h

Removed: 
    


################################################################################
diff  --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index f69f366c1750918..38377f01a10086f 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -710,9 +710,13 @@ class Sema final {
     return result;
   }
 
+  // Saves the current floating-point pragma stack and clear it in this Sema.
   class FpPragmaStackSaveRAII {
   public:
-    FpPragmaStackSaveRAII(Sema &S) : S(S), SavedStack(S.FpPragmaStack) {}
+    FpPragmaStackSaveRAII(Sema &S)
+        : S(S), SavedStack(std::move(S.FpPragmaStack)) {
+      S.FpPragmaStack.Stack.clear();
+    }
     ~FpPragmaStackSaveRAII() { S.FpPragmaStack = std::move(SavedStack); }
 
   private:
@@ -722,7 +726,6 @@ class Sema final {
 
   void resetFPOptions(FPOptions FPO) {
     CurFPFeatures = FPO;
-    FpPragmaStack.Stack.clear();
     FpPragmaStack.CurrentValue = FPO.getChangesFrom(FPOptions(LangOpts));
   }
 

diff  --git a/clang/test/Sema/PR69717.cpp b/clang/test/Sema/PR69717.cpp
new file mode 100644
index 000000000000000..3207092b948ae86
--- /dev/null
+++ b/clang/test/Sema/PR69717.cpp
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -verify -fsyntax-only %s
+// expected-no-diagnostics
+
+// Testcase for https://github.com/llvm/llvm-project/issues/69717
+
+#pragma float_control(precise, on, push)
+
+template<typename T>
+constexpr T multi(T x, T y) {
+  return x * y;
+}
+
+int multi_i(int x, int y) {
+  return multi<int>(x, y);
+}
+
+#pragma float_control(pop)