From 5e044c673f8e7d473a2207cd3ba32910c4f5fc75 Mon Sep 17 00:00:00 2001
From: Tom de Vries <tdevries@suse.de>
Date: Fri, 11 Sep 2020 07:13:25 +0200
Subject: [PATCH] [nvptx] Fix UB in nvptx_assemble_value

When nvptx_assemble_value is called with size == 16, this bitshift runs
into UB:
...
  val &= ((unsigned  HOST_WIDE_INT)2 << (size * BITS_PER_UNIT - 1)) - 1;
...

Fix this by checking the shift amount.

Tested on nvptx.

gcc/ChangeLog:

	* config/nvptx/nvptx.c (nvptx_assemble_value): Fix undefined
	behaviour.
---
 gcc/config/nvptx/nvptx.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/gcc/config/nvptx/nvptx.c b/gcc/config/nvptx/nvptx.c
index 4fca0ed76d9..0c590d8d1f6 100644
--- a/gcc/config/nvptx/nvptx.c
+++ b/gcc/config/nvptx/nvptx.c
@@ -2053,7 +2053,9 @@ nvptx_assemble_value (unsigned HOST_WIDE_INT val, unsigned size)
   bool negative_p
     = val & (HOST_WIDE_INT_1U << (HOST_BITS_PER_WIDE_INT - 1));
 
-  val &= ((unsigned  HOST_WIDE_INT)2 << (size * BITS_PER_UNIT - 1)) - 1;
+  /* Avoid undefined behaviour.  */
+  if (size * BITS_PER_UNIT < HOST_BITS_PER_WIDE_INT)
+    val &= (HOST_WIDE_INT_1U << (size * BITS_PER_UNIT)) - 1;
 
   for (unsigned part = 0; size; size -= part)
     {