Configure BOLT behavior through BOLT_{COMMON,APPLY}_FLAGS (#1178)

Configure BOLT behavior using the `BOLT_COMMON_FLAGS` and
`BOLT_APPLY_FLAGS` environment variables. The existing BOLT behavior is
preserved.

Previously patches were used to modify the default values defined in
configure.ac

This approach allows complete control over the BOLT behavior and makes
the configuration easier to test, debug and update in the future.

Would make the existing patches unnecessary. 
closes #877 
closes #878 
closes #879

Author: jjhelmus

cpython-unix/build-cpython.sh

@@ -226,31 +226,6 @@ if [ -n "${PYTHON_MEETS_MINIMUM_VERSION_3_11}" ]; then
     patch -p1 -i "${ROOT}/patch-pwd-remove-conditional.patch"
 fi
 
-if [ -n "${PYTHON_MEETS_MINIMUM_VERSION_3_12}" ]; then
-    # Additional BOLT optimizations, being upstreamed in
-    # https://github.com/python/cpython/issues/128514
-    patch -p1 -i "${ROOT}/patch-configure-bolt-apply-flags-128514.patch"
-
-    # Disable unsafe identical code folding. Objects/typeobject.c
-    # update_one_slot requires that wrap_binaryfunc != wrap_binaryfunc_l,
-    # despite the functions being identical.
-    # https://github.com/python/cpython/pull/134642
-    patch -p1 -i "${ROOT}/patch-configure-bolt-icf-safe.patch"
-
-    # Tweak --skip-funcs to work with our toolchain.
-    if [ -n "${PYTHON_MEETS_MINIMUM_VERSION_3_15}" ]; then
-        patch -p1 -i "${ROOT}/patch-configure-bolt-skip-funcs-3.15.patch"
-    else
-        patch -p1 -i "${ROOT}/patch-configure-bolt-skip-funcs.patch"
-    fi
-
-    # Remove -use-gnu-stack from the BOLT optimization flags as it incorrectly
-    # removes the PT_GNU_STACK segment. This patch can be removed when this bug
-    # is fixed in LLVM.
-    # https://github.com/llvm/llvm-project/issues/174191
-    patch -p1 -i "${ROOT}/patch-configure-bolt-remove-use-gnu-stack.patch"
-fi
-
 # The optimization make targets are both phony and non-phony. This leads
 # to PGO targets getting reevaluated after a build when you use multiple
 # make invocations. e.g. `make install` like we do below. Fix that.
@@ -498,6 +473,31 @@ if [ -n "${CPYTHON_OPTIMIZED}" ]; then
     CONFIGURE_FLAGS="${CONFIGURE_FLAGS} --enable-optimizations"
     if [[ -n "${PYTHON_MEETS_MINIMUM_VERSION_3_12}" && -n "${BOLT_CAPABLE}" ]]; then
         CONFIGURE_FLAGS="${CONFIGURE_FLAGS} --enable-bolt"
+
+        # CPython allows overriding the default BOLT flags via configure
+        # environment variables. Use our toolchain-specific skip list, add
+        # additional optimizations, use safe identical code folding, and omit
+        # -use-gnu-stack because it incorrectly removes the PT_GNU_STACK
+        # segment.
+        # https://github.com/python/cpython/issues/128514
+        # https://github.com/python/cpython/pull/134642
+        # https://github.com/llvm/llvm-project/issues/174191
+        BOLT_COMMON_FLAGS="-update-debug-sections -skip-funcs=RC4_options/1"
+        BOLT_APPLY_FLAGS="${BOLT_COMMON_FLAGS} \
+-reorder-blocks=ext-tsp \
+-reorder-functions=cdsort \
+-split-functions \
+-split-strategy=cdsplit \
+-icf=safe \
+-inline-all \
+-split-eh \
+-reorder-functions-use-hot-size \
+-peepholes=none \
+-jump-tables=aggressive \
+-inline-ap \
+-indirect-call-promotion=all \
+-dyno-stats \
+-frame-opt=hot"
     fi
 
     # Allow users to enable the experimental JIT on 3.13+
@@ -774,7 +774,8 @@ if [[ -n "${PYTHON_MEETS_MINIMUM_VERSION_3_14}" && "${TARGET_TRIPLE}" == x86_64*
     CFLAGS_JIT="${CFLAGS_JIT//-fPIC/}"
 fi
 
-CFLAGS=$CFLAGS CPPFLAGS=$CFLAGS CFLAGS_JIT=$CFLAGS_JIT LDFLAGS=$LDFLAGS \
+BOLT_COMMON_FLAGS="${BOLT_COMMON_FLAGS:-}" BOLT_APPLY_FLAGS="${BOLT_APPLY_FLAGS:-}" \
+    CFLAGS=$CFLAGS CPPFLAGS=$CFLAGS CFLAGS_JIT=$CFLAGS_JIT LDFLAGS=$LDFLAGS \
     ./configure ${CONFIGURE_FLAGS}
 
 # Supplement produced Makefile with our modifications.