From: Roger Sayle <roger@nextmovesoftware.com>
Date: Mon, 23 Aug 2021 14:35:05 +0000 (+0100)
Subject: [Committed] Restore build on !TARGET_TRULY_NOOP_TRUNCATION targets
X-Git-Tag: basepoints/gcc-13~5227
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=89ff4f027b5c92e96a8527920b8ccc3b94aec672;p=thirdparty%2Fgcc.git

[Committed] Restore build on !TARGET_TRULY_NOOP_TRUNCATION targets

My sincere apologies to everyone, but especially Andrew Pinski
who warned me in advance that TRULY_NOOP_TRUNCATION results in
different code paths/optimizations on some targets. This restores
the build on nvptx-none (and presumably others) where mysteriously
(truncate:QI (reg:QI)) fails to be simplified to (reg:QI), which
is expected (everywhere) in my recently added self-tests.

2021-08-23  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* simplify-rtx.c (simplify_unary_operation_1): [TRUNCATE]:
	Handle case where the operand is already the desired mode.
---

diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index f3df6140766f..8eea9fb7e0a6 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -1268,6 +1268,9 @@ simplify_context::simplify_unary_operation_1 (rtx_code code, machine_mode mode,
 	    return temp;
 	}
 
+      /* Check for useless truncation.  */
+      if (GET_MODE (op) == mode)
+	return op;
       break;
 
     case FLOAT_TRUNCATE: