Re: Floating-point comparisons in the middle-end

[FX <fxcoudert@gmail.com>]

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Hi,

> Dunno if we really need a builtin for this, especially if it is lowered
> to that x >= y && x <= y early, will defer to Joseph.

I think it’d be nice to have one for consistency, as the other standard floating-point functions are there. It would also make things slightly easier for our Fortran implementation, although admittedly we can do without.

A tentative patch is attached, it seems to work well on simple examples, but for test coverage the hard part is going to be that the comparisons seem to be optimised away very easily into their non-signaling versions. Basically, if I do:

  float x = __builtin_nanf("");
  printf("%d\n", __builtin_iseqsig(__builtin_nanf(""), __builtin_inff()));
  printf("%d\n", __builtin_iseqsig(x, __builtin_inff()));

With -O0 -fno-unsafe-math-optimizations -frounding-math -fsignaling-nans: first one does not raise invalid, second one does.
With -O2 -fno-unsafe-math-optimizations -frounding-math -fsignaling-nans: no invalid raised at all.

FX


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diff --git a/gcc/builtins.cc b/gcc/builtins.cc
index f1f7c0ce337..bf6bf2809d8 100644
--- a/gcc/builtins.cc
+++ b/gcc/builtins.cc
@@ -171,6 +171,7 @@ static tree fold_builtin_fabs (location_t, tree, tree);
 static tree fold_builtin_abs (location_t, tree, tree);
 static tree fold_builtin_unordered_cmp (location_t, tree, tree, tree, enum tree_code,
 					enum tree_code);
+static tree fold_builtin_iseqsig (location_t, tree, tree);
 static tree fold_builtin_varargs (location_t, tree, tree*, int);
 
 static tree fold_builtin_strpbrk (location_t, tree, tree, tree, tree);
@@ -9404,6 +9405,42 @@ fold_builtin_unordered_cmp (location_t loc, tree fndecl, tree arg0, tree arg1,
 		      fold_build2_loc (loc, code, type, arg0, arg1));
 }
 
+/* Fold a call to __builtin_iseqsig().  ARG0 and ARG1 are the arguments.
+   After choosing the wider floating-point type for the comparison,
+   the code is folded to:
+     SAVE_EXPR<ARG0> >= SAVE_EXPR<ARG1> && SAVE_EXPR<ARG0> <= SAVE_EXPR<ARG1>  */
+
+static tree
+fold_builtin_iseqsig (location_t loc, tree arg0, tree arg1)
+{
+  tree type0, type1;
+  enum tree_code code0, code1;
+  tree cmp1, cmp2, cmp_type = NULL_TREE;
+
+  type0 = TREE_TYPE (arg0);
+  type1 = TREE_TYPE (arg1);
+
+  code0 = TREE_CODE (type0);
+  code1 = TREE_CODE (type1);
+
+  if (code0 == REAL_TYPE && code1 == REAL_TYPE)
+    /* Choose the wider of two real types.  */
+    cmp_type = TYPE_PRECISION (type0) >= TYPE_PRECISION (type1)
+      ? type0 : type1;
+  else if (code0 == REAL_TYPE && code1 == INTEGER_TYPE)
+    cmp_type = type0;
+  else if (code0 == INTEGER_TYPE && code1 == REAL_TYPE)
+    cmp_type = type1;
+
+  arg0 = builtin_save_expr (fold_convert_loc (loc, cmp_type, arg0));
+  arg1 = builtin_save_expr (fold_convert_loc (loc, cmp_type, arg1));
+
+  cmp1 = fold_build2_loc (loc, GE_EXPR, integer_type_node, arg0, arg1);
+  cmp2 = fold_build2_loc (loc, LE_EXPR, integer_type_node, arg0, arg1);
+
+  return fold_build2_loc (loc, TRUTH_AND_EXPR, integer_type_node, cmp1, cmp2);
+}
+
 /* Fold __builtin_{,s,u}{add,sub,mul}{,l,ll}_overflow, either into normal
    arithmetics if it can never overflow, or into internal functions that
    return both result of arithmetics and overflowed boolean flag in
@@ -9791,6 +9828,9 @@ fold_builtin_2 (location_t loc, tree expr, tree fndecl, tree arg0, tree arg1)
 					 arg0, arg1, UNORDERED_EXPR,
 					 NOP_EXPR);
 
+    case BUILT_IN_ISEQSIG:
+      return fold_builtin_iseqsig (loc, arg0, arg1);
+
       /* We do the folding for va_start in the expander.  */
     case BUILT_IN_VA_START:
       break;
@@ -11303,6 +11343,7 @@ is_inexpensive_builtin (tree decl)
       case BUILT_IN_ISLESSEQUAL:
       case BUILT_IN_ISLESSGREATER:
       case BUILT_IN_ISUNORDERED:
+      case BUILT_IN_ISEQSIG:
       case BUILT_IN_VA_ARG_PACK:
       case BUILT_IN_VA_ARG_PACK_LEN:
       case BUILT_IN_VA_COPY:
diff --git a/gcc/builtins.def b/gcc/builtins.def
index f0236316850..8fab9dc3f1b 100644
--- a/gcc/builtins.def
+++ b/gcc/builtins.def
@@ -908,6 +908,7 @@ DEF_GCC_BUILTIN        (BUILT_IN_ISLESS, "isless", BT_FN_INT_VAR, ATTR_CONST_NOT
 DEF_GCC_BUILTIN        (BUILT_IN_ISLESSEQUAL, "islessequal", BT_FN_INT_VAR, ATTR_CONST_NOTHROW_TYPEGENERIC_LEAF)
 DEF_GCC_BUILTIN        (BUILT_IN_ISLESSGREATER, "islessgreater", BT_FN_INT_VAR, ATTR_CONST_NOTHROW_TYPEGENERIC_LEAF)
 DEF_GCC_BUILTIN        (BUILT_IN_ISUNORDERED, "isunordered", BT_FN_INT_VAR, ATTR_CONST_NOTHROW_TYPEGENERIC_LEAF)
+DEF_GCC_BUILTIN        (BUILT_IN_ISEQSIG, "iseqsig", BT_FN_INT_VAR, ATTR_CONST_NOTHROW_TYPEGENERIC_LEAF)
 DEF_GCC_BUILTIN        (BUILT_IN_ISSIGNALING, "issignaling", BT_FN_INT_VAR, ATTR_CONST_NOTHROW_TYPEGENERIC_LEAF)
 DEF_LIB_BUILTIN        (BUILT_IN_LABS, "labs", BT_FN_LONG_LONG, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C99_BUILTIN        (BUILT_IN_LLABS, "llabs", BT_FN_LONGLONG_LONGLONG, ATTR_CONST_NOTHROW_LEAF_LIST)
diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
index 1eb842e1c7b..44d30436e47 100644
--- a/gcc/c-family/c-common.cc
+++ b/gcc/c-family/c-common.cc
@@ -6330,6 +6330,7 @@ check_builtin_function_arguments (location_t loc, vec<location_t> arg_loc,
     case BUILT_IN_ISLESSEQUAL:
     case BUILT_IN_ISLESSGREATER:
     case BUILT_IN_ISUNORDERED:
+    case BUILT_IN_ISEQSIG:
       if (builtin_function_validate_nargs (loc, fndecl, nargs, 2))
 	{
 	  enum tree_code code0, code1;