make/autoconf/flags-cflags.m4

rev 54643 : 8220388: Increase -inlinehint-threshold for Clang to avoid G1 pause time regression
Summary: Make Clang inline more aggressively for functions with inline keyword
Reviewed-by:

*** 534,543 ****
--- 534,549 ----
      # src/hotspot/cpu/*/globalDefinitions_*.hpp files, but this value currently
      # works for all platforms.
      TOOLCHAIN_CFLAGS_JVM="$TOOLCHAIN_CFLAGS_JVM -mno-omit-leaf-frame-pointer -mstack-alignment=16"
  
      if test "x$OPENJDK_TARGET_OS" = xlinux; then
+       if test "x$DEBUG_LEVEL" = xrelease; then
+         # Clang does not inline as much as GCC does for functions with "inline" keyword by default.
+         # This causes noticeable slowdown in pause time for G1, and possibly in other areas.
+         # Increasing the inline hint threshold avoids the slowdown for Clang-built JVM.
+         TOOLCHAIN_CFLAGS_JVM="$TOOLCHAIN_CFLAGS_JVM -mllvm -inlinehint-threshold=100000"
+       fi
        TOOLCHAIN_CFLAGS_JDK="-pipe"
        TOOLCHAIN_CFLAGS_JDK_CONLY="-fno-strict-aliasing" # technically NOT for CXX
      fi
    elif test "x$TOOLCHAIN_TYPE" = xsolstudio; then
      TOOLCHAIN_FLAGS="-errtags -errfmt"