|
|
@@ -0,0 +1,116 @@
|
|
|
+From: Ramin Moussavi <ramin.moussavi@yacoub.de>
|
|
|
+Date: Sat May 16 16:00:00 2026 +0000
|
|
|
+Subject: [PATCH] builtins: fix __builtin_iseqsig dropping FE_INVALID under -O2
|
|
|
+
|
|
|
+`__builtin_iseqsig` (added in r14-... by commit
|
|
|
+34cf27a64e7af949538e65bc266963c24f8da458) silently fails to raise
|
|
|
+FE_INVALID on a quiet-NaN operand under -O2 on ARM and other targets
|
|
|
+where signaling and quiet IEEE 754 comparisons map to different machine
|
|
|
+instructions (ARM VCMPE vs VCMP, x86 UCOMISS vs COMISS).
|
|
|
+
|
|
|
+The tests added by that commit -- gcc.dg/torture/builtin-iseqsig-{1,2,3}.c --
|
|
|
+have been observed FAILing on:
|
|
|
+
|
|
|
+ * arm-linux-gnueabihf, GCC 14.2 native (Debian), -Os
|
|
|
+ https://lists.debian.org/debian-gcc/2024/08/msg00143.html
|
|
|
+ * arm-bbs-linux-uclibcgnueabihf, GCC 15.2 cross,
|
|
|
+ -O2 and the LTO torture iterations
|
|
|
+
|
|
|
+Two interacting issues:
|
|
|
+
|
|
|
+1. BUILT_IN_ISEQSIG was registered with ATTR_CONST_NOTHROW_TYPEGENERIC_LEAF.
|
|
|
+ That matches the other IS* predicates (isgreater, isless, ...), which
|
|
|
+ are *quiet* per IEEE 754. But iseqsig is the *signaling* equality:
|
|
|
+ per IEEE 754 it must raise FE_INVALID on any NaN operand, both quiet
|
|
|
+ and signaling. Marking it CONST tells the middle-end it has no side
|
|
|
+ effect.
|
|
|
+
|
|
|
+2. fold_builtin_iseqsig folds the call to
|
|
|
+ "(a >= b) && (a <= b)" using TRUTH_AND_EXPR (non-short-circuit).
|
|
|
+ That is gimplified to BIT_AND_EXPR, producing a linear "compute both
|
|
|
+ comparison flags then AND" sequence. The RTL scheduler is then free
|
|
|
+ to reorder the signaling VCMPE compares around fenv reads -- e.g.
|
|
|
+ fetestexcept(FE_INVALID) -- silently dropping the FE_INVALID side
|
|
|
+ effect that the comparisons raise on NaN.
|
|
|
+
|
|
|
+ The same source-level expression "(a >= b) && (a <= b)" written by
|
|
|
+ the user works correctly: && is parsed as TRUTH_ANDIF_EXPR, which
|
|
|
+ gimplifies to a branched if-then-else where the first comparison
|
|
|
+ stays anchored as a branch condition and cannot move across other
|
|
|
+ side-effecting calls.
|
|
|
+
|
|
|
+Fix:
|
|
|
+
|
|
|
+ - Drop ATTR_CONST_NOTHROW_TYPEGENERIC_LEAF, use
|
|
|
+ ATTR_NOTHROW_TYPEGENERIC_LEAF (already defined in builtin-attrs.def,
|
|
|
+ previously unused).
|
|
|
+
|
|
|
+ - Fold using TRUTH_ANDIF_EXPR rather than TRUTH_AND_EXPR.
|
|
|
+
|
|
|
+After this patch, gcc.dg/torture/builtin-iseqsig-{1,2,3}.c PASS on
|
|
|
+arm-bbs-linux-uclibcgnueabihf (cortex-a5, neon-vfpv4, hard float,
|
|
|
+uClibc-ng) at every torture option:
|
|
|
+
|
|
|
+ -O0, -O1, -O2, -O3, -Os, -O2 -flto -fno-fat-lto-objects,
|
|
|
+ -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects
|
|
|
+
|
|
|
+The same harness reproduces the FAIL on stock 15.2.0 sources and PASSes
|
|
|
+with this patch applied.
|
|
|
+
|
|
|
+Related: PR middle-end/34678, PR middle-end/38960.
|
|
|
+
|
|
|
+gcc/
|
|
|
+ * builtins.def (BUILT_IN_ISEQSIG): Drop ATTR_CONST; iseqsig has
|
|
|
+ an observable fenv side effect (FE_INVALID), unlike the other IS*
|
|
|
+ predicates which are quiet per IEEE 754.
|
|
|
+ * builtins.cc (fold_builtin_iseqsig): Fold using TRUTH_ANDIF_EXPR
|
|
|
+ rather than TRUTH_AND_EXPR. The former gimplifies to a branched
|
|
|
+ if-then-else where the leading signaling comparison is anchored
|
|
|
+ as a branch condition; the latter gimplifies to BIT_AND_EXPR,
|
|
|
+ which the RTL scheduler may reorder around fenv reads, dropping
|
|
|
+ the FE_INVALID side effect.
|
|
|
+
|
|
|
+Signed-off-by: Ramin Moussavi <ramin.moussavi@yacoub.de>
|
|
|
+---
|
|
|
+ gcc/builtins.cc | 12 +++++++++++-
|
|
|
+ gcc/builtins.def | 6 +++++-
|
|
|
+ 2 files changed, 16 insertions(+), 2 deletions(-)
|
|
|
+
|
|
|
+diff --git a/gcc/builtins.cc b/gcc/builtins.cc
|
|
|
+--- a/gcc/builtins.cc
|
|
|
++++ b/gcc/builtins.cc
|
|
|
+@@ -10098,7 +10098,17 @@ fold_builtin_iseqsig (location_t loc, tree arg0, tree arg1)
|
|
|
+ cmp1 = fold_build2_loc (loc, GE_EXPR, integer_type_node, arg0, arg1);
|
|
|
+ cmp2 = fold_build2_loc (loc, LE_EXPR, integer_type_node, arg0, arg1);
|
|
|
+
|
|
|
+- return fold_build2_loc (loc, TRUTH_AND_EXPR, integer_type_node, cmp1, cmp2);
|
|
|
++ /* Use short-circuit && (TRUTH_ANDIF_EXPR) rather than & (TRUTH_AND_EXPR).
|
|
|
++ TRUTH_AND_EXPR is gimplified to BIT_AND_EXPR, producing a linear
|
|
|
++ "compute both flags then AND" sequence that the RTL scheduler may
|
|
|
++ reorder around fenv reads (fetestexcept) - silently dropping the
|
|
|
++ FE_INVALID side effect that the signaling GE/LE comparisons must
|
|
|
++ raise on NaN operands. TRUTH_ANDIF_EXPR gimplifies to a branched
|
|
|
++ if-then-else where the first comparison stays anchored as a
|
|
|
++ branch condition, so the signaling VCMPE (ARM) / UCOMISS (x86)
|
|
|
++ cannot move across other side-effecting calls. */
|
|
|
++ return fold_build2_loc (loc, TRUTH_ANDIF_EXPR, integer_type_node,
|
|
|
++ cmp1, cmp2);
|
|
|
+ }
|
|
|
+
|
|
|
+ /* Fold __builtin_{,s,u}{add,sub,mul}{,l,ll}_overflow, either into normal
|
|
|
+diff --git a/gcc/builtins.def b/gcc/builtins.def
|
|
|
+--- a/gcc/builtins.def
|
|
|
++++ b/gcc/builtins.def
|
|
|
+@@ -1072,7 +1072,11 @@ DEF_GCC_BUILTIN (BUILT_IN_ISLESS, "isless", BT_FN_INT_VAR, ATTR_CONST_NOT
|
|
|
+ DEF_GCC_BUILTIN (BUILT_IN_ISLESSEQUAL, "islessequal", BT_FN_INT_VAR, ATTR_CONST_NOTHROW_TYPEGENERIC_LEAF)
|
|
|
+ DEF_GCC_BUILTIN (BUILT_IN_ISLESSGREATER, "islessgreater", BT_FN_INT_VAR, ATTR_CONST_NOTHROW_TYPEGENERIC_LEAF)
|
|
|
+ DEF_GCC_BUILTIN (BUILT_IN_ISUNORDERED, "isunordered", BT_FN_INT_VAR, ATTR_CONST_NOTHROW_TYPEGENERIC_LEAF)
|
|
|
+-DEF_GCC_BUILTIN (BUILT_IN_ISEQSIG, "iseqsig", BT_FN_INT_VAR, ATTR_CONST_NOTHROW_TYPEGENERIC_LEAF)
|
|
|
++/* iseqsig is the SIGNALING variant of equality: per IEEE 754 it must
|
|
|
++ raise FE_INVALID on any NaN operand (both quiet and signaling NaNs).
|
|
|
++ Unlike the other IS* predicates (which are quiet) it has an observable
|
|
|
++ fenv side effect, so it must NOT carry the const attribute. */
|
|
|
++DEF_GCC_BUILTIN (BUILT_IN_ISEQSIG, "iseqsig", BT_FN_INT_VAR, ATTR_NOTHROW_TYPEGENERIC_LEAF)
|
|
|
+ DEF_GCC_BUILTIN (BUILT_IN_ISSIGNALING, "issignaling", BT_FN_INT_VAR, ATTR_CONST_NOTHROW_TYPEGENERIC_LEAF)
|
|
|
+ DEF_LIB_BUILTIN (BUILT_IN_LABS, "labs", BT_FN_LONG_LONG, ATTR_CONST_NOTHROW_LEAF_LIST)
|
|
|
+ DEF_C99_BUILTIN (BUILT_IN_LLABS, "llabs", BT_FN_LONGLONG_LONGLONG, ATTR_CONST_NOTHROW_LEAF_LIST)
|
Waldemar Brodkorb