[clang] Fix -fno-unsafe-math-optimizations behavior (PR #89473)

[Andy Kaylor via cfe-commits]

https://github.com/andykaylor updated https://github.com/llvm/llvm-project/pull/89473

>From a137c023aaf5ccc174d347b7bda403bf15d683ae Mon Sep 17 00:00:00 2001
From: Andy Kaylor <andrew.kaylor at intel.com>
Date: Wed, 24 Apr 2024 12:35:49 -0700
Subject: [PATCH] Fix -fno-unsafe-math-optimizations behavior

This changes the handling of -fno-unsafe-fp-math to stop having that
option imply -ftrapping-math. In gcc, -fno-unsafe-math-optimizations sets
-ftrapping-math, but that dependency is based on the fact the
-ftrapping-math is enabled by default in gcc. Because clang does not
enabled -ftrapping-math by default, there is no reason for
-fno-unsafe-math-optimizations to set it.

On the other hand, -funsafe-math-optimizations continues to imply
-fno-trapping-math because this option necessarily disables strict
exception semantics.

This fixes https://github.com/llvm/llvm-project/issues/87523
---
 clang/docs/UsersManual.rst            | 1 -
 clang/lib/Driver/ToolChains/Clang.cpp | 2 --
 clang/test/Driver/fast-math.c         | 7 +++----
 3 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst
index 8df40566fcba3d..fb0ade943999a5 100644
--- a/clang/docs/UsersManual.rst
+++ b/clang/docs/UsersManual.rst
@@ -1690,7 +1690,6 @@ floating point semantic models: precise (the default), strict, and fast.
    * ``-fno-associative-math``
    * ``-fno-reciprocal-math``
    * ``-fsigned-zeros``
-   * ``-ftrapping-math``
    * ``-ffp-contract=on``
    * ``-fdenormal-fp-math=ieee``
 
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 5f5d720cf759f4..a4755248180294 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -3151,8 +3151,6 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
       ReciprocalMath = false;
       SignedZeros = true;
       ApproxFunc = false;
-      TrappingMath = true;
-      FPExceptionBehavior = "strict";
 
       // The target may have opted to flush by default, so force IEEE.
       DenormalFPMath = llvm::DenormalMode::getIEEE();
diff --git a/clang/test/Driver/fast-math.c b/clang/test/Driver/fast-math.c
index b07d5732932cdb..274f1f22ea5e9e 100644
--- a/clang/test/Driver/fast-math.c
+++ b/clang/test/Driver/fast-math.c
@@ -157,7 +157,7 @@
 
 // FIXME: This case leaves nnan and ninf. That seems wrong!
 // RUN: %clang -### -ffast-math -fno-unsafe-math-optimizations -c %s 2>&1 \
-// RUN:   | FileCheck --check-prefixes=CHECK,NO-FAST,NINF,NNAN,FINITE-ONLY,NO-REASSOC,NO-NSZ,NO-ARCP,NO-AFN,NOROUNDING %s
+// RUN:   | FileCheck --check-prefixes=CHECK,NO-FAST,NINF,NNAN,FINITE-ONLY,NO-REASSOC,NO-NSZ,NO-ARCP,NO-AFN,NOROUNDING,NO-TRAPPING %s
 // RUN: %clang -### -ffast-math -fmath-errno -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefixes=CHECK,NO-FAST,NINF,NNAN,FINITE-ONLY,REASSOC,NSZ,ARCP,AFN,CONTRACT-FAST,ERRNO,NOROUNDING %s
 // RUN: %clang -### -ffast-math -fno-associative-math -c %s 2>&1 \
@@ -209,7 +209,7 @@
 
 // RUN: %clang -### -funsafe-math-optimizations -fno-unsafe-math-optimizations \
 // RUN:     -c %s 2>&1 \
-// RUN:   | FileCheck --check-prefixes=CHECK,NO-UNSAFE,NO-REASSOC,NO-ARCP,NO-NSZ,NO-AFN %s
+// RUN:   | FileCheck --check-prefixes=CHECK,NO-UNSAFE,NO-REASSOC,NO-ARCP,NO-NSZ,NO-AFN,NO-TRAPPING %s
 // RUN: %clang -### -ffast-math -fno-associative-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefixes=CHECK,NO-UNSAFE,NO-REASSOC,ARCP,NSZ,AFN %s
 
@@ -224,9 +224,8 @@
 // RUN: %clang -### -ffast-math -ftrapping-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefixes=CHECK,NO-FAST,NO-UNSAFE,ARCP,NSZ,AFN,TRAPPING %s
 
-// FIXME: -fno-unsafe-math-optimizations shouldn't imply trapping math
 // RUN: %clang -### -ffast-math -fno-unsafe-math-optimizations -c %s 2>&1 \
-// RUN:   | FileCheck --check-prefixes=CHECK,NO-FAST,NO-UNSAFE,NO-ARCP,NO-NSZ,NO-AFN,TRAPPING %s
+// RUN:   | FileCheck --check-prefixes=CHECK,NO-FAST,NO-UNSAFE,NO-ARCP,NO-NSZ,NO-AFN,NO-TRAPPING %s
 
 // Reassociate is allowed because it does not require reciprocal-math.