c-family: Cast __atomic_load_*/__atomic_exchange_* result to _BitInt rather then...

As written in the PR, torture/bitint-64.c test fails with -O2 -flto
and the reason is that on _BitInt arches where the padding bits
are undefined, the padding bits in the _Atomic vars are also undefined,
but when __atomic_load or __atomic_exchange on a _BitInt _Atomic variable
with some padding bits is lowered into __atomic_load_{1,2,4,8,16} or
__atomic_exchange_*, the mode precision unsigned result is VIEW_CONVERT_EXPR
converted to _BitInt and because of the VCE nothing actually sign/zero
extends it as needed for later uses - the var is no longer addressable and
expansion assumes such automatic vars are properly extended.

The following patch fixes that by using NOP_EXPR on it (the
VIEW_CONVERT_EXPR after it will then be optimized away during
gimplification, didn't want to repeat it in the code as else result = build1
(VIEW_CONVERT_EXPR, ...); twice.

2024-03-27  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/114469
	* c-common.cc (resolve_overloaded_builtin): For _BitInt result
	on !extended targets convert result to the _BitInt type before
	using VIEW_CONVERT_EXPR.

diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
index 48844b17f77a64805feae60177f4b6765edfc607..6fa8243b02b5eda3c427cc210c58e3ed677d8460 100644 (file)
--- a/gcc/c-family/c-common.cc
+++ b/gcc/c-family/c-common.cc
@@ -8461,7 +8461,19 @@ resolve_overloaded_builtin (location_t loc, tree function,
        if (new_return)
          {
            /* Cast function result from I{1,2,4,8,16} to the required type.  */
-           result = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (new_return), result);
+           if (TREE_CODE (TREE_TYPE (new_return)) == BITINT_TYPE)
+             {
+               struct bitint_info info;
+               unsigned prec = TYPE_PRECISION (TREE_TYPE (new_return));
+               targetm.c.bitint_type_info (prec, &info);
+               if (!info.extended)
+                 /* For _BitInt which has the padding bits undefined
+                    convert to the _BitInt type rather than VCE to force
+                    zero or sign extension.  */
+                 result = build1 (NOP_EXPR, TREE_TYPE (new_return), result);
+             }
+           result
+             = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (new_return), result);
            result = build2 (MODIFY_EXPR, TREE_TYPE (new_return), new_return,
                             result);
            TREE_SIDE_EFFECTS (result) = 1;