Fix -fno-unsafe-math-optimizations behavior (#89473)

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
enable -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 #87523

Author: Andy Kaylor

clang/docs/UsersManual.rst

@@ -1696,7 +1696,6 @@ for more details.
    * ``-fno-associative-math``
    * ``-fno-reciprocal-math``
    * ``-fsigned-zeros``
-   * ``-ftrapping-math``
    * ``-ffp-contract=on``
 
    There is ambiguity about how ``-ffp-contract``,

clang/lib/Driver/ToolChains/Clang.cpp

@@ -3112,8 +3112,6 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
       ReciprocalMath = false;
       SignedZeros = true;
       ApproxFunc = false;
-      TrappingMath = true;
-      FPExceptionBehavior = "strict";
 
       if (!JA.isDeviceOffloading(Action::OFK_Cuda) &&
           !JA.isOffloading(Action::OFK_HIP)) {

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.