[llvm][nsan] Skip function declarations (#105598)

Skip function declarations in the instrumentation pass.

Author: alexander-shaposhnikov

llvm/lib/Transforms/Instrumentation/NumericalStabilitySanitizer.cpp

@@ -2038,7 +2038,8 @@ static void moveFastMathFlags(Function &F,
 
 bool NumericalStabilitySanitizer::sanitizeFunction(
     Function &F, const TargetLibraryInfo &TLI) {
-  if (!F.hasFnAttribute(Attribute::SanitizeNumericalStability))
+  if (!F.hasFnAttribute(Attribute::SanitizeNumericalStability) ||
+      F.isDeclaration())
     return false;
 
   // This is required to prevent instrumenting call to __nsan_init from within

llvm/test/Instrumentation/NumericalStabilitySanitizer/basic.ll

@@ -4,6 +4,8 @@
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 
+declare float @declaration_only(float %a) sanitize_numerical_stability
+
 ; Tests with simple control flow.
 
 @float_const = private unnamed_addr constant float 0.5