expmed: Always use QImode for init_expmed set_zero_cost [PR119785]

This is a regression on some targets introduced I believe by r6-2055
which added mode argument to set_src_cost.

The problem here is that in the first iteration, mode is always QImode
and we get as -Os zero cost set_src_cost (const0_rtx, QImode, false).
But then we use the mode variable for iterating over int, partial int
and vector int modes, so for the second iteration we call set_src_cost
with mode which is at that time (machine_mode) (MAX_MODE_VECTOR_INT + 1).

In the x86 case that happens to be V2HFmode and we don't crash (and
compute the same 0 cost as we would for QImode).
But e.g. in the SPARC case (machine_mode) (MAX_MODE_VECTOR_INT + 1) is
MAX_MACHINE_MODE and that does all kinds of weird things especially
when doing ubsan bootstrap.

Fixed by always using QImode.

2025-04-14  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/119785
	* expmed.cc (init_expmed): Always pass QImode rather than mode to
	set_src_cost passed to set_zero_cost.

(cherry picked from commit f96a54350afcf7f3c90d0ecb51d7683d826acc00)

diff --git a/gcc/expmed.cc b/gcc/expmed.cc
index 39e53faec70eacef28f9f7a99165354ac650b551..9c3bf094f8962b3b00506b5f13d1fdbb32d54831 100644 (file)
--- a/gcc/expmed.cc
+++ b/gcc/expmed.cc
@@ -284,7 +284,7 @@ init_expmed (void)
   for (speed = 0; speed < 2; speed++)
     {
       crtl->maybe_hot_insn_p = speed;
-      set_zero_cost (speed, set_src_cost (const0_rtx, mode, speed));
+      set_zero_cost (speed, set_src_cost (const0_rtx, QImode, speed));
 
       for (mode = MIN_MODE_INT; mode <= MAX_MODE_INT;
           mode = (machine_mode)(mode + 1))