Blame SOURCES/jdk8210416-rh1632174-compile_fdlibm_with_o2_ffp_contract_off_on_gcc_clang_arches.patch

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# HG changeset patch
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# User sgehwolf
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# Date 1536142767 -7200
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#      Wed Sep 05 12:19:27 2018 +0200
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# Node ID 7ea57274e55054579d1532e757edb21e67beed83
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# Parent  3ee91722550680c18b977f0e00b1013323b5c9ef
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8210416: [linux] Poor StrictMath performance due to non-optimized compilation
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Summary: Compile fdlibm with -O2 -ffp-contract=off on gcc/clang arches.
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Reviewed-by: aph, erikj, dholmes, darcy
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diff --git a/make/autoconf/flags-cflags.m4 b/make/autoconf/flags-cflags.m4
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--- a/make/autoconf/flags-cflags.m4
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+++ b/make/autoconf/flags-cflags.m4
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@@ -366,6 +366,18 @@
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   FLAGS_SETUP_CFLAGS_CPU_DEP([BUILD], [OPENJDK_BUILD_])
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+  COMPILER_FP_CONTRACT_OFF_FLAG="-ffp-contract=off"
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+  # Check that the compiler supports -ffp-contract=off flag
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+  # Set FDLIBM_CFLAGS to -ffp-contract=off if it does. Empty
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+  # otherwise.
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+  # These flags are required for GCC-based builds of
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+  # fdlibm with optimization without losing precision.
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+  # Notably, -ffp-contract=off needs to be added for GCC >= 4.6.
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+  FLAGS_COMPILER_CHECK_ARGUMENTS(ARGUMENT: [${COMPILER_FP_CONTRACT_OFF_FLAG}],
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+      IF_TRUE: [FDLIBM_CFLAGS=${COMPILER_FP_CONTRACT_OFF_FLAG}],
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+      IF_FALSE: [FDLIBM_CFLAGS=""])
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+  AC_SUBST(FDLIBM_CFLAGS)
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+
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   # Tests are only ever compiled for TARGET
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   CFLAGS_TESTLIB="$CFLAGS_JDKLIB"
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   CXXFLAGS_TESTLIB="$CXXFLAGS_JDKLIB"
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diff --git a/make/autoconf/spec.gmk.in b/make/autoconf/spec.gmk.in
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--- a/make/autoconf/spec.gmk.in
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+++ b/make/autoconf/spec.gmk.in
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@@ -444,6 +444,7 @@
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 LIBJSIG_HASHSTYLE_LDFLAGS := @LIBJSIG_HASHSTYLE_LDFLAGS@
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 LIBJSIG_NOEXECSTACK_LDFLAGS := @LIBJSIG_NOEXECSTACK_LDFLAGS@
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+FDLIBM_CFLAGS := @FDLIBM_CFLAGS@
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 JVM_CFLAGS := @JVM_CFLAGS@
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 JVM_LDFLAGS := @JVM_LDFLAGS@
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 JVM_ASFLAGS := @JVM_ASFLAGS@
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diff --git a/make/lib/CoreLibraries.gmk b/make/lib/CoreLibraries.gmk
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--- a/make/lib/CoreLibraries.gmk
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+++ b/make/lib/CoreLibraries.gmk
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@@ -39,20 +39,15 @@
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   BUILD_LIBFDLIBM_OPTIMIZATION := HIGH
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 endif
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-ifeq ($(OPENJDK_TARGET_OS), linux)
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-  ifeq ($(OPENJDK_TARGET_CPU), ppc64)
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-    BUILD_LIBFDLIBM_OPTIMIZATION := HIGH
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-  else ifeq ($(OPENJDK_TARGET_CPU), ppc64le)
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-    BUILD_LIBFDLIBM_OPTIMIZATION := HIGH
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-  else ifeq ($(OPENJDK_TARGET_CPU), s390x)
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-    BUILD_LIBFDLIBM_OPTIMIZATION := HIGH
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-  else ifeq ($(OPENJDK_TARGET_CPU), aarch64)
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-    BUILD_LIBFDLIBM_OPTIMIZATION := HIGH
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-  endif
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+# If FDLIBM_CFLAGS is non-empty we know that we can optimize
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+# fdlibm by adding those extra C flags. Currently GCC,
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+# and clang only.
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+ifneq ($(FDLIBM_CFLAGS), )
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+  BUILD_LIBFDLIBM_OPTIMIZATION := LOW
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 endif
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 LIBFDLIBM_SRC := $(TOPDIR)/src/java.base/share/native/libfdlibm
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-LIBFDLIBM_CFLAGS := -I$(LIBFDLIBM_SRC)
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+LIBFDLIBM_CFLAGS := -I$(LIBFDLIBM_SRC) $(FDLIBM_CFLAGS)
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 ifneq ($(OPENJDK_TARGET_OS), macosx)
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   $(eval $(call SetupNativeCompilation, BUILD_LIBFDLIBM, \
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@@ -64,10 +59,6 @@
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       CFLAGS := $(CFLAGS_JDKLIB) $(LIBFDLIBM_CFLAGS), \
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       CFLAGS_windows_debug := -DLOGGING, \
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       CFLAGS_aix := -qfloat=nomaf, \
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-      CFLAGS_linux_ppc64 := -ffp-contract=off, \
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-      CFLAGS_linux_ppc64le := -ffp-contract=off, \
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-      CFLAGS_linux_s390x := -ffp-contract=off, \
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-      CFLAGS_linux_aarch64 := -ffp-contract=off, \
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       DISABLED_WARNINGS_gcc := sign-compare misleading-indentation array-bounds, \
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       DISABLED_WARNINGS_microsoft := 4146 4244 4018, \
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       ARFLAGS := $(ARFLAGS), \