AIX: workaround the aix FP glibc bug

Due to a bug on AIX, some of the glibc FP functions do not
preserve the sign bit when a negative input is passed by
value and the output is rounded to 0:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97086

This CL forces the use of "-0.0" in such cases.

Change-Id: If9935596e32e97720f3cb22f27975267ac1124d7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2468618Reviewed-by: Zhi An Ng <zhin@chromium.org>
Commit-Queue: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/master@{#70512}

src/utils/utils.h

@@ -708,6 +708,19 @@ static inline V ByteReverse(V value) {
   }
 }
 
+#if V8_OS_AIX
+// glibc on aix has a bug when using ceil, trunc or nearbyint:
+// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97086
+template <typename T>
+T FpOpWorkaround(T input, T value) {
+  if (/*if -*/ std::signbit(input) && value == 0.0 &&
+      /*if +*/ !std::signbit(value)) {
+    return -0.0;
+  }
+  return value;
+}
+#endif
+
 V8_EXPORT_PRIVATE bool PassesFilter(Vector<const char> name,
                                     Vector<const char> filter);
 

src/wasm/wasm-external-refs.cc

@@ -405,9 +405,12 @@ template <typename T, T (*float_round_op)(T)>
 void simd_float_round_wrapper(Address data) {
   constexpr int n = kSimd128Size / sizeof(T);
   for (int i = 0; i < n; i++) {
-    WriteUnalignedValue<T>(
-        data + (i * sizeof(T)),
-        float_round_op(ReadUnalignedValue<T>(data + (i * sizeof(T)))));
+    T input = ReadUnalignedValue<T>(data + (i * sizeof(T)));
+    T value = float_round_op(input);
+#if V8_OS_AIX
+    value = FpOpWorkaround<T>(input, value);
+#endif
+    WriteUnalignedValue<T>(data + (i * sizeof(T)), value);
   }
 }
 

test/cctest/cctest.status

@@ -396,13 +396,6 @@
   # TODO(ppc): Implement load/store reverse byte instructions
   'test-run-wasm-simd/RunWasm_SimdLoadStoreLoad': [SKIP],
   'test-run-wasm-simd/RunWasm_SimdLoadStoreLoad_turbofan': [SKIP],
-  # TODO(miladfarca): remove once aix gcc bug is fixed.
-  # gcc on aix has a bug when using ceilf or truncf:
-  # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97086
-  'test-run-wasm-simd/RunWasm_F32x4Ceil_*': [SKIP],
-  'test-run-wasm-simd/RunWasm_F32x4Trunc_*': [SKIP],
-  'test-run-wasm-simd/RunWasm_F64x2Ceil_*': [SKIP],
-  'test-run-wasm-simd/RunWasm_F64x2Trunc_*': [SKIP],
 
 }],  # 'system == aix or (arch == ppc64 and byteorder == big)'
 

test/cctest/wasm/test-run-wasm-simd.cc

@@ -586,6 +586,9 @@ void RunF32x4UnOpTest(TestExecutionTier execution_tier, LowerSimd lower_simd,
     // Extreme values have larger errors so skip them for approximation tests.
     if (!exact && IsExtreme(x)) continue;
     float expected = expected_op(x);
+#if V8_OS_AIX
+    expected = FpOpWorkaround<float>(x, expected);
+#endif
     if (!PlatformCanRepresent(expected)) continue;
     r.Call(x);
     for (int i = 0; i < 4; i++) {
@@ -1176,6 +1179,9 @@ void RunF64x2UnOpTest(TestExecutionTier execution_tier, LowerSimd lower_simd,
     // Extreme values have larger errors so skip them for approximation tests.
     if (!exact && IsExtreme(x)) continue;
     double expected = expected_op(x);
+#if V8_OS_AIX
+    expected = FpOpWorkaround<double>(x, expected);
+#endif
     if (!PlatformCanRepresent(expected)) continue;
     r.Call(x);
     for (int i = 0; i < 2; i++) {