simplify-rtx: Fix up last argument to simplify_gen_unary [PR113656]

When simplifying e.g. (float_truncate:SF (float_truncate:DF (reg:XF))
or (float_truncate:SF (float_extend:XF (reg:DF)) etc. into
(float_truncate:SF (reg:XF)) or (float_truncate:SF (reg:DF)) we call
simplify_gen_unary with incorrect op_mode argument, it should be
the argument's mode, but we call it with the outer mode instead.
As these are all floating point operations, the argument always
has non-VOIDmode and so we can just use that mode (as done in similar
simplifications a few lines later), but neither FLOAT_TRUNCATE nor
FLOAT_EXTEND are operations that should have the same modes of operand
and result.  This bug hasn't been a problem for years because normally
op_mode is used only if the mode of op is VOIDmode, otherwise it is
redundant, but r10-2139 added an assertion in some spots that op_mode
is right even in such cases.

2024-01-31  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/113656
	* simplify-rtx.cc (simplify_context::simplify_unary_operation_1)
	<case FLOAT_TRUNCATE>: Fix up last argument to simplify_gen_unary.

	* gcc.target/i386/pr113656.c: New test.

(cherry picked from commit b59775b642bb2b1ecd2e6d52c988b9c432117bc8)

diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
index ee75079917f8359dbb8bfa378a8a634894105b30..33fa88d369d96045d8d12c8127f0a9f201d372fc 100644 (file)
--- a/gcc/simplify-rtx.cc
+++ b/gcc/simplify-rtx.cc
@@ -1305,7 +1305,7 @@ simplify_context::simplify_unary_operation_1 (rtx_code code, machine_mode mode,
                                   > GET_MODE_UNIT_SIZE (mode)
                                   ? FLOAT_TRUNCATE : FLOAT_EXTEND,
                                   mode,
-                                  XEXP (op, 0), mode);
+                                  XEXP (op, 0), GET_MODE (XEXP (op, 0)));
 
       /*  (float_truncate (float x)) is (float x)  */
       if ((GET_CODE (op) == FLOAT || GET_CODE (op) == UNSIGNED_FLOAT)

diff --git a/gcc/testsuite/gcc.target/i386/pr113656.c b/gcc/testsuite/gcc.target/i386/pr113656.c
new file mode 100644 (file)
index 0000000..fa57a56
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr113656.c
@@ -0,0 +1,12 @@
+/* PR rtl-optimization/113656 */
+/* { dg-do compile } */
+/* { dg-options "-O3 -frounding-math -funsafe-math-optimizations -mavx512fp16 -mavx512vl" } */
+
+_Float16 a[8];
+
+void
+foo ()
+{
+  for (int i = 0; i < 8; i++)
+    a[i] = i - 8.4;
+}