diff mbox series

[committed] combine: Punt on out of range rotate counts [PR93505]

Message ID 20200130203927.GP17695@tucnak
State New
Headers show
Series [committed] combine: Punt on out of range rotate counts [PR93505] | expand

Commit Message

Jakub Jelinek Jan. 30, 2020, 8:39 p.m. UTC 
Hi!

What happens on this testcase is with the out of bounds rotate we get:
Trying 13 -> 16:
   13: r129:SI=r132:DI#0<-<0x20
       REG_DEAD r132:DI
   16: r123:DI=r129:SI<0
       REG_DEAD r129:SI
Successfully matched this instruction:
(set (reg/v:DI 123 [ <retval> ])
     (const_int 0 [0]))
during combine.  So, perhaps we could also change simplify-rtx.c to punt
if it is out of bounds rather than trying to optimize anything.
Or, but probably GCC11 material, if we decide that ROTATE/ROTATERT doesn't
have out of bounds counts or introduce targetm.rotate_truncation_mask,
we should truncate the argument instead of punting.
Punting is better for backports though.

Bootstrapped/regtested on powerpc64{,le}-linux, preapproved by Segher in the
PR, committed to trunk.

2020-01-30  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/93505
	* combine.c (simplify_comparison) <case ROTATE>: Punt on out of range
	rotate counts.

	* gcc.c-torture/compile/pr93505.c: New test.



	Jakub
diff mbox series

Patch

--- gcc/combine.c.jj	2020-01-12 11:54:36.222416290 +0100
+++ gcc/combine.c	2020-01-30 15:08:13.607205111 +0100
@@ -12410,7 +12410,8 @@  simplify_comparison (enum rtx_code code,
 	     bit.  This will be converted into a ZERO_EXTRACT.  */
 	  if (const_op == 0 && sign_bit_comparison_p
 	      && CONST_INT_P (XEXP (op0, 1))
-	      && mode_width <= HOST_BITS_PER_WIDE_INT)
+	      && mode_width <= HOST_BITS_PER_WIDE_INT
+	      && UINTVAL (XEXP (op0, 1)) < mode_width)
 	    {
 	      op0 = simplify_and_const_int (NULL_RTX, mode, XEXP (op0, 0),
 					    (HOST_WIDE_INT_1U
--- gcc/testsuite/gcc.c-torture/compile/pr93505.c.jj	2020-01-30 15:23:19.919634317 +0100
+++ gcc/testsuite/gcc.c-torture/compile/pr93505.c	2020-01-30 15:22:59.537939346 +0100
@@ -0,0 +1,15 @@ 
+/* PR middle-end/93505 */
+
+unsigned a;
+
+unsigned
+foo (unsigned x)
+{
+  unsigned int y = 32 - __builtin_bswap64 (-a);
+  /* This would be UB (x << 32) at runtime.  Ensure we don't
+     invoke UB in the compiler because of that (visible with
+     bootstrap-ubsan).  */
+  x = x << y | x >> (-y & 31);
+  x >>= 31;
+  return x;
+}