From 919c9d4bd3db7da09061af3b6f2a9193bf7bae45 Mon Sep 17 00:00:00 2001
From: Roger Sayle <roger@nextmovesoftware.com>
Date: Mon, 3 Aug 2020 13:15:58 +0100
Subject: [PATCH] PR rtl-optimization 61494: Preserve x-0.0 with HONOR_SNANS.
The following patch avoids simplifying x-0.0 to x when -fsignaling-nans
is specified, which resolves PR rtl-optimization 61494. Indeed, running
the test program attached to that PR now reports no failures.
2020-08-02 Roger Sayle <roger@nextmovesoftware.com>
gcc/ChangeLog
PR rtl-optimization/61494
* simplify-rtx.c (simplify_binary_operation_1) [MINUS]: Don't
simplify x - 0.0 with -fsignaling-nans.
---
gcc/simplify-rtx.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index d2211686accf..4f0652f553ec 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -2678,11 +2678,12 @@ simplify_binary_operation_1 (enum rtx_code code, machine_mode mode,
&& !contains_symbolic_reference_p (op1))
return simplify_gen_unary (NOT, mode, op1, mode);
- /* Subtracting 0 has no effect unless the mode has signed zeros
- and supports rounding towards -infinity. In such a case,
- 0 - 0 is -0. */
+ /* Subtracting 0 has no effect unless the mode has signalling NaNs,
+ or has signed zeros and supports rounding towards -infinity.
+ In such a case, 0 - 0 is -0. */
if (!(HONOR_SIGNED_ZEROS (mode)
&& HONOR_SIGN_DEPENDENT_ROUNDING (mode))
+ && !HONOR_SNANS (mode)
&& trueop1 == CONST0_RTX (mode))
return op0;