ci: add -Werror strict lane and auto-discovered regression harness

Two pieces of CI hardening (#315):

* WERROR opt-in (Make.inc) and a dedicated `strict-werror` CI job that
  builds with -Werror under both gcc and clang on a pinned ubuntu-24.04.
  It is off by default and pinned so a future compiler upgrade surfaces
  as one isolated failure rather than breaking the whole matrix. Fixes
  the warnings this surfaces in openlibm's own code:
    - irint(): mark the header-defined helper __unused (it is only used
      by e_rem_pio2*.c, so it is unused in every other TU).
    - lgamma_r/lgammal_r: zero-init nadj, which is written and read under
      the same hx<0 guard (-Wmaybe-uninitialized false positive).
  Clang-only -Wimplicit-int-float-conversion (intentional lround
  boundary trick) and -Wignored-attributes (pre-existing extern-inline
  fenv redeclarations) are documented and suppressed for the lane.

* Regression harness: test/regression/*.c are self-contained programs
  (exit 0=pass, 77=skip, else=fail) auto-discovered and run by
  `make test` from the repo root, so later fixes can land a regression
  test by dropping in one file with no Makefile changes. The previously
  orphaned test-211.c (never built or run) is moved in as the first one.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ViralBShah

.github/workflows/ci.yml

@@ -52,6 +52,25 @@ jobs:
           install: base-devel mingw-w64-${{matrix.env}}-toolchain
       - run: make -j$(nproc)
       - run: make test
+  strict-warnings:
+    # Dedicated -Werror lane. Pinned to a fixed image (not ubuntu-latest) so a
+    # compiler upgrade surfaces here as an explicit, isolated failure instead of
+    # breaking the whole matrix. See WERROR in Make.inc.
+    name: strict-werror (${{ matrix.cc }})
+    runs-on: ubuntu-24.04
+    timeout-minutes: 10
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - { cc: gcc,   flags: "" }
+          - { cc: clang, flags: "USECLANG=1 USEGCC=0" }
+    steps:
+      - uses: actions/checkout@v7
+      - name: Build with -Werror
+        run: make -j$(nproc) WERROR=1 ${{ matrix.flags }}
+      - name: Test
+        run: make test ${{ matrix.flags }}
   code-coverage:
     runs-on: ubuntu-latest
     timeout-minutes: 10

Make.inc

@@ -159,6 +159,21 @@ SFLAGS_add  += $(SFLAGS_arch)
 LDFLAGS_add += $(LDFLAGS_arch)
 
 CFLAGS_add += -std=c99 -Wall -I$(OPENLIBM_HOME) -I$(OPENLIBM_HOME)/include -I$(OPENLIBM_HOME)/$(ARCH) -I$(OPENLIBM_HOME)/src -DASSEMBLER -D__BSD_VISIBLE -Wno-implicit-function-declaration
+
+# Treat warnings as errors. Off by default so a compiler upgrade can't break a
+# normal build; a dedicated CI lane sets WERROR=1 to catch new warnings early.
+WERROR ?= 0
+ifeq ($(WERROR),1)
+CFLAGS_add += -Werror
+# Two clang-only diagnostics are silenced for the strict lane (gcc ignores
+# unknown -Wno-* options, so this is safe for both compilers):
+#  * -Wimplicit-int-float-conversion: s_lround/s_llround deliberately round
+#    DTYPE_MAX through (dtype)x; the boundary arithmetic is correct by design.
+#  * -Wignored-attributes: the extern-inline fenv re-declarations in
+#    openlibm_fenv_*.h trip a harmless attribute-placement diagnostic; tracked
+#    separately rather than reworked under the warnings sweep.
+CFLAGS_add += -Wno-implicit-int-float-conversion -Wno-ignored-attributes
+endif
 ifneq ($(filter $(ARCH),i387 amd64 powerpc),)
 CFLAGS_add += -I$(OPENLIBM_HOME)/ld80
 else

Makefile

@@ -49,9 +49,15 @@ endif
 LDFLAGS_add += -Wl,$(SONAME_FLAG),libopenlibm.$(OLM_MAJOR_SHLIB_EXT)
 endif
 
-.PHONY: all check test clean distclean \
+.PHONY: all check test test-regression clean distclean \
 	install install-static install-shared install-pkgconfig install-headers
 
+# Per-issue regression programs live in test/regression/*.c. They are run from
+# the repo root (like test-double/test-float) so the freshly built shared
+# library is found the same way on every platform.
+REGRESSION_SRCS := $(sort $(wildcard test/regression/*.c))
+REGRESSION_BINS := $(REGRESSION_SRCS:.c=)
+
 
 OLM_LIBS := libopenlibm.a
 ifneq ($(ARCH), wasm32)
@@ -63,6 +69,21 @@ all : $(OLM_LIBS)
 check test: test/test-double test/test-float
 	test/test-double
 	test/test-float
+	$(MAKE) test-regression
+
+# Build (in test/) then run each regression program from the repo root.
+# Exit status 0 = pass, 77 = skipped (not applicable here), anything else = fail.
+test-regression: libopenlibm.$(OLM_MAJOR_MINOR_SHLIB_EXT)
+	$(MAKE) -C test regression-build
+	@pass=0; skip=0; fail=0; \
+	for t in $(REGRESSION_BINS); do \
+		./$$t; rc=$$?; \
+		if [ "$$rc" = "0" ]; then echo "  PASS $$t"; pass=`expr $$pass + 1`; \
+		elif [ "$$rc" = "77" ]; then echo "  SKIP $$t"; skip=`expr $$skip + 1`; \
+		else echo "  FAIL $$t (exit $$rc)"; fail=`expr $$fail + 1`; fi; \
+	done; \
+	echo "regression: $$pass passed, $$skip skipped, $$fail failed"; \
+	[ "$$fail" = "0" ]
 
 libopenlibm.a: $(OBJS)
 	$(AR) -rcs libopenlibm.a $(OBJS)

ld80/e_lgammal_r.c

@@ -271,6 +271,7 @@ lgammal_r(long double x, int *signgamp)
   long double t, y, z, nadj, p, p1, p2, q, r, w;
   int i, ix;
   u_int32_t se, i0, i1;
+  nadj = 0;	/* only set & used when hx<0; init silences -Wmaybe-uninitialized */
 
   *signgamp = 1;
   GET_LDOUBLE_WORDS (se, i0, i1, x);

src/e_lgamma_r.c

@@ -208,6 +208,7 @@ __ieee754_lgamma_r(double x, int *signgamp)
 	double t,y,z,nadj,p,p1,p2,p3,q,r,w;
 	int32_t hx;
 	int i,lx,ix;
+	nadj = 0;	/* only set & used when hx<0; init silences -Wmaybe-uninitialized */
 
 	EXTRACT_WORDS(hx,lx,x);
 

src/math_private.h

@@ -253,7 +253,7 @@ void __scan_nan(u_int32_t *__words, int __num_words, const char *__s);
 /* Asm versions of some functions. */
 
 #ifdef __amd64__
-static __inline int
+static __inline int __attribute__((__unused__))
 irint(double x)
 {
 	int n;
@@ -265,7 +265,7 @@ irint(double x)
 #endif
 
 #ifdef __i386__
-static __inline int
+static __inline int __attribute__((__unused__))
 irint(double x)
 {
 	int n;

test/.gitignore

@@ -7,3 +7,8 @@
 /bench-openlibm
 /bench-syslibm
 /*.exe
+# Built regression programs (keep the .c sources and the shared header).
+/regression/test-*
+!/regression/test-*.c
+/regression/*.exe
+/regression/*.dSYM

test/Makefile

@@ -13,6 +13,17 @@ endif
 
 all: test-double test-float # test-double-system test-float-system
 
+# Per-issue regression tests: every test/regression/*.c is a self-contained
+# program named after the issue it covers. New files are picked up automatically
+# (no Makefile edit needed); the top-level Makefile runs them via `make test`.
+REGRESSION_SRCS := $(sort $(wildcard regression/*.c))
+REGRESSION_BINS := $(REGRESSION_SRCS:.c=)
+
+regression-build: $(REGRESSION_BINS)
+
+regression/%: regression/%.c regression/regress-util.h
+	$(CC) $(CPPFLAGS) $(CFLAGS) $(CFLAGS_add) $(LDFLAGS) $(LDFLAGS_arch) $< -D__BSD_VISIBLE -I ../include -I../src $(OPENLIBM_LIB) -o $@
+
 bench: bench-syslibm bench-openlibm
 
 test-double: test-double.c libm-test.c libm-test-ulps.h
@@ -35,3 +46,6 @@ bench-syslibm: libm-bench.cpp
 
 clean:
 	rm -fr test-double test-float test-double-system test-float-system bench-openlibm bench-syslibm *.dSYM
+	rm -fr $(REGRESSION_BINS) $(addsuffix .exe,$(REGRESSION_BINS)) regression/*.dSYM
+
+.PHONY: all bench regression-build clean

test/regression/regress-util.h

@@ -0,0 +1,31 @@
+/*
+ * Minimal helpers for openlibm standalone regression tests.
+ *
+ * Each regression test is a self-contained program named after the issue it
+ * covers (test/regression/test-<issue>.c).  The harness in test/Makefile builds
+ * and runs every file in this directory and interprets the exit status as:
+ *
+ *     0   the test passed
+ *     77  the test does not apply on this platform and was skipped
+ *     *   the test failed
+ *
+ * Use REGRESS_SKIP for the skip status and CHECK() for assertions so a failing
+ * test prints which condition broke and where.
+ */
+#ifndef OPENLIBM_REGRESS_UTIL_H
+#define OPENLIBM_REGRESS_UTIL_H
+
+#include <stdio.h>
+
+#define REGRESS_SKIP 77
+
+#define CHECK(cond)							\
+	do {								\
+		if (!(cond)) {						\
+			fprintf(stderr, "  check failed: %s (%s:%d)\n",	\
+			    #cond, __FILE__, __LINE__);			\
+			return 1;					\
+		}							\
+	} while (0)
+
+#endif /* OPENLIBM_REGRESS_UTIL_H */

test/regression/test-211.c

@@ -0,0 +1,21 @@
+/*
+ * Regression test for issue #211: loss of precision in powf.
+ * https://github.com/JuliaMath/openlibm/issues/211
+ *
+ * Fixed in 98f8713 by importing the latest msun powf; this pins the exact
+ * result so the regression cannot silently return.
+ */
+#include <math.h>
+
+#include "regress-util.h"
+
+int
+main(void)
+{
+	float x = 0xd.65874p-4f;
+	float y = 4.0f;
+	float z = powf(x, y);
+
+	CHECK(z == 0x1.f74424p-2f);
+	return 0;
+}