[llvm] LangRef: Clarify behaviors of nsz in fast math flag (PR #137567)

[YunQiang Su via llvm-commits]

https://github.com/wzssyqa updated https://github.com/llvm/llvm-project/pull/137567

>From a25d5dcb4d84124ce525777bd1ff209bb5d0a8ce Mon Sep 17 00:00:00 2001
From: YunQiang Su <yunqiang at isrc.iscas.ac.cn>
Date: Mon, 28 Apr 2025 08:54:40 +0800
Subject: [PATCH 1/2] LangRef: Clarify nsz on min/max operations for +0.0 vs
 -0.0

On min/max operations, now +0.0 is treated greater than -0.0. To
ignore this behaivor (fmin/fmax of libc doesn't require it), let's
use `nsz` for this case.
---
 llvm/docs/LangRef.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index 5bd1d29487139..12d5a7fe8c419 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -3914,6 +3914,10 @@ following flags to enable otherwise unsafe floating-point transformations.
    No Signed Zeros - Allow optimizations to treat the sign of a zero
    argument or zero result as insignificant. This does not imply that -0.0
    is poison and/or guaranteed to not exist in the operation.
+   Don't require +0.0>-0.0 for min/max operations - Allow optimizations of the
+   min/max operation not to treat +0.0>-0.0. Note the result should be either of
+   the operands. (max|min)(-0.0, -0.0) should never return +0.0, and vice versa.
+   Note: floating compare operations always imply -0.0 == +0.0.
 
 Note: For :ref:`phi <i_phi>`, :ref:`select <i_select>`, and :ref:`call <i_call>`
 instructions, the following return types are considered to be floating-point

>From 918e5ace424288661b666d255b8419319359de7e Mon Sep 17 00:00:00 2001
From: YunQiang Su <yunqiang at isrc.iscas.ac.cn>
Date: Thu, 8 May 2025 09:36:01 +0800
Subject: [PATCH 2/2] Rewording

---
 llvm/docs/LangRef.rst | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index 12d5a7fe8c419..6f2a1b6c9ee3b 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -3914,10 +3914,11 @@ following flags to enable otherwise unsafe floating-point transformations.
    No Signed Zeros - Allow optimizations to treat the sign of a zero
    argument or zero result as insignificant. This does not imply that -0.0
    is poison and/or guaranteed to not exist in the operation.
-   Don't require +0.0>-0.0 for min/max operations - Allow optimizations of the
-   min/max operation not to treat +0.0>-0.0. Note the result should be either of
-   the operands. (max|min)(-0.0, -0.0) should never return +0.0, and vice versa.
-   Note: floating compare operations always imply -0.0 == +0.0.
+   For fcmp, this has no effect. For min/max intrinsics, this allows
+   returning either +0 or -0 if both +0 and -0 are passed.
+   For calls to anything other than a min/max intrinsic,
+   arithmetic instructions, select, and phi, if the result is zero,
+   the returned value can be a zero of either sign.
 
 Note: For :ref:`phi <i_phi>`, :ref:`select <i_select>`, and :ref:`call <i_call>`
 instructions, the following return types are considered to be floating-point