[PATCH] D154359: [clang] Reset FP options before template instantiation

[Serge Pavlov via Phabricator via cfe-commits]

sepavloff created this revision.
sepavloff added reviewers: rsmith, rjmccall, aaron.ballman, efriedma.
Herald added a project: All.
sepavloff requested review of this revision.
Herald added a project: clang.

AST nodes that may depend on FP options keep them as a difference
relative to the options outside the AST node. At the moment of
instantiation the FP options may be different from the default values,
defined by command-line option. In such case FP attributes would have
unexpected values. For example, the code:

  template <class C> void func_01(int last, C) {
    func_01(last, int());
  }
  void func_02() { func_01(0, 1); }
  #pragma STDC FENV_ACCESS ON

caused compiler crash, because template instantiation takes place at the
end of translation unit, where pragma STDC FENV_ACCESS is in effect. As
a result, code in the template instantiation would use constrained
intrinsics while the function does not have StrictFP attribute.

To solve this problem, FP attributes in Sema must be set to default
values, defined by command line options.

This change resolves https://github.com/llvm/llvm-project/issues/63542.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D154359

Files:
  clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
  clang/test/CodeGen/fp-template.cpp


Index: clang/test/CodeGen/fp-template.cpp
===================================================================
--- clang/test/CodeGen/fp-template.cpp
+++ clang/test/CodeGen/fp-template.cpp
@@ -15,4 +15,19 @@
 // CHECK-SAME:  (float noundef %{{.*}}, float noundef %{{.*}}) #[[ATTR01:[0-9]+]]{{.*}} {
 // CHECK:       call float @llvm.experimental.constrained.fadd.f32
 
+namespace PR63542 {
+  template <class Compare> float stable_sort(float x, Compare) {
+    float result = x + x;
+    stable_sort(x, int());
+    return result;
+  }
+  float linkage_wrap() { return stable_sort(0.0, 1); }
+}
+
+// CHECK-LABEL: define {{.*}} float @_ZN7PR6354211stable_sortIiEEffT_(
+// CHECK:         fadd float
+
+// Must be at the end of translation unit.
+#pragma STDC FENV_ACCESS ON
+
 // CHECK: attributes #[[ATTR01]] = { {{.*}}strictfp
Index: clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
===================================================================
--- clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -5087,6 +5087,10 @@
     // PushDeclContext because we don't have a scope.
     Sema::ContextRAII savedContext(*this, Function);
 
+    FPFeaturesStateRAII SavedFPFeatures(*this);
+    CurFPFeatures = FPOptions(getLangOpts());
+    FpPragmaStack.CurrentValue = FPOptionsOverride();
+
     if (addInstantiatedParametersToScope(Function, PatternDecl, Scope,
                                          TemplateArgs))
       return;


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