[PATCH 0/2] MR8474: configure: Build PEs with -ffp-exception-behavior=maytrap.

[Jacek Caban (＠jacek)]

Fixes gdiplus tests in Clang build.

When the compiler assumes non-trapping floating-point math, it may apply more aggressive optimizations. For example, in the fast path of `GdipInvertMatrix`, it may merge paired divisions into a single `divss` instruction. This can leave unused lanes whose results are ignored, but they still execute and may cause a division by zero, breaking tests that have the FP exception mask enabled.

Using `-ffp-exception-behavior=maytrap` prevents the compiler from performing such transformations.

It's a bit surprising that this flag also disables optimizations like those seen in the dmime tests, so there’s likely room for improvement on the compiler side. Regardless, relying on `round()` in tests isn't valid, as it's not available in msvcrt.dll and may depend on compiler-specific behavior.

[PATCH 1/2] configure: Build PEs with -ffp-exception-behavior=maytrap.

[Jacek Caban]

From: Jacek Caban

Fixes gdiplus tests in Clang build.
---
 configure.ac | 1 +
 1 file changed, 1 insertion(+)

diff --git a/configure.ac b/configure.ac
index c408e3788d6..ff306d6a98e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -565,6 +565,7 @@ This is an error since --enable-archs=$wine_arch was requested.])])
     WINE_TRY_PE_CFLAGS([-Wenum-enum-conversion],[:],WINE_TRY_PE_CFLAGS([-Wenum-conversion]))
     WINE_TRY_PE_CFLAGS([-ffunction-sections])
     WINE_TRY_PE_CFLAGS([-fasync-exceptions -DMIN_CLANG_VERSION=19], AS_VAR_APPEND([${wine_arch}_EXTRACFLAGS],[" -fasync-exceptions"]))
+    WINE_TRY_PE_CFLAGS([-ffp-exception-behavior=maytrap])

dnl clang had broken -fms-hotpatch support before version 18 (https://github.com/llvm/llvm-project/pull/77245)
     WINE_TRY_PE_CFLAGS([-fms-hotpatch -DMIN_CLANG_VERSION=18],

[PATCH 2/2] dmime/tests: Use ceil instead of round.

[Jacek Caban]

From: Jacek Caban

round is not available in msvcrt.dll. While it’s typically handled via a compiler
builtin, that’s not the case with Clang when -ffp-exception-behavior=maytrap is used.
---
 dlls/dmime/tests/dmime.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dlls/dmime/tests/dmime.c b/dlls/dmime/tests/dmime.c
index 2329a1411ba..389f2546c01 100644
--- a/dlls/dmime/tests/dmime.c
+++ b/dlls/dmime/tests/dmime.c
@@ -4090,7 +4090,7 @@ static void test_wave_pmsg(unsigned num_repeats)
     hr = IDirectMusicPerformance_ReferenceToMusicTime(performance, 1000000, &length);
     ok(hr == S_OK, "got %#lx\n", hr);
     /* assuming not modified tempo */
-    length = round((1000000 * 120.0 * DMUS_PPQ) / 600000000.0);
+    length = ceil((1000000 * 120.0 * DMUS_PPQ) / 600000000.0);

for (i = 0; i <= num_repeats; i++)
     {