explow: Fix ICE caused by plus_constant [PR94002]

The following testcase ICEs in cross to riscv64-linux.  The problem is
that we have a DImode integral constant (that doesn't fit into SImode),
which is pushed into a constant pool and later access just the first half of
it using a MEM.  When plus_constant is called on such a MEM, if the constant
has mode, we verify the mode, but if it doesn't, we don't and ICE later on
when we think the CONST_INT is a valid SImode constant.

2020-03-03  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/94002
	* explow.c (plus_constant): Punt if cst has VOIDmode and
	get_pool_mode is different from mode.

	* gcc.dg/pr94002.c: New test.

gcc/ChangeLog

+2020-03-03  Jakub Jelinek  <jakub@redhat.com>
+
+	PR rtl-optimization/94002
+	* explow.c (plus_constant): Punt if cst has VOIDmode and
+	get_pool_mode is different from mode.
+
 2020-03-03  Claudiu Zissulescu  <claziss@synopsys.com>
 
 	* config/arc/arc.c (leigitimate_small_data_address_p): Check if an

gcc/explow.c

@@ -128,6 +128,9 @@ plus_constant (machine_mode mode, rtx x, poly_int64 c, bool inplace)
 	      cst = gen_lowpart (mode, cst);
 	      gcc_assert (cst);
 	    }
+	  else if (GET_MODE (cst) == VOIDmode
+		   && get_pool_mode (XEXP (x, 0)) != mode)
+	    break;
 	  if (GET_MODE (cst) == VOIDmode || GET_MODE (cst) == mode)
 	    {
 	      tem = plus_constant (mode, cst, c);

gcc/testsuite/ChangeLog

 2020-03-03  Jakub Jelinek  <jakub@redhat.com>
 
+	PR rtl-optimization/94002
+	* gcc.dg/pr94002.c: New test.
+
 	PR tree-optimization/93927
 	* gcc.c-torture/compile/pr93927-1.c: New test.
 	* gcc.c-torture/compile/pr93927-2.c: New test.

gcc/testsuite/gcc.dg/pr94002.c

+/* PR rtl-optimization/94002 */
+/* { dg-do compile } */
+/* { dg-options "-O1 -fno-tree-dce -fno-tree-reassoc" } */
+/* { dg-additional-options "-fPIC" { target fpic } } */
+
+unsigned a, b;
+
+void
+foo (void)
+{
+  __builtin_sub_overflow (b, 44852956282LL, &a);
+  a += ~b;
+}