Hello world, Following Richard's suggestion, I have implemented the GFC_ASSERT macro and used it to (hopefully) silence the ominous warning and allow further optimization.
OK for trunk? Regards Thomas 2017-03-12 Thomas Koenig <tkoe...@gcc.gnu.org> PR libfortran/79956 * libgfortran.h (GFC_ASSERT): New macro. * m4/reshape.m4 (reshape_'rtype_ccode`): Use GFC_ASSERT to specify that sdim > 0. * intrinsic/reshape_generic.c (reshape_internal): Likweise. * generated/reshape_c10.c: Regenerated. * generated/reshape_c16.c: Regenerated. * generated/reshape_c4.c: Regenerated. * generated/reshape_c8.c: Regenerated. * generated/reshape_i16.c: Regenerated. * generated/reshape_i4.c: Regenerated. * generated/reshape_i8.c: Regenerated. * generated/reshape_r10.c: Regenerated. * generated/reshape_r16.c: Regenerated. * generated/reshape_r4.c: Regenerated. * generated/reshape_r8.c: Regenerated.
Index: generated/reshape_c10.c =================================================================== --- generated/reshape_c10.c (Revision 245760) +++ generated/reshape_c10.c (Arbeitskopie) @@ -232,6 +232,11 @@ reshape_c10 (gfc_array_c10 * const restrict ret, } sdim = GFC_DESCRIPTOR_RANK (source); + + /* sdim is always > 0; this lets the compiler optimize more and + avoids a warning. */ + GFC_ASSERT(sdim>0); + ssize = 1; sempty = 0; for (n = 0; n < sdim; n++) Index: generated/reshape_c16.c =================================================================== --- generated/reshape_c16.c (Revision 245760) +++ generated/reshape_c16.c (Arbeitskopie) @@ -232,6 +232,11 @@ reshape_c16 (gfc_array_c16 * const restrict ret, } sdim = GFC_DESCRIPTOR_RANK (source); + + /* sdim is always > 0; this lets the compiler optimize more and + avoids a warning. */ + GFC_ASSERT(sdim>0); + ssize = 1; sempty = 0; for (n = 0; n < sdim; n++) Index: generated/reshape_c4.c =================================================================== --- generated/reshape_c4.c (Revision 245760) +++ generated/reshape_c4.c (Arbeitskopie) @@ -232,6 +232,11 @@ reshape_c4 (gfc_array_c4 * const restrict ret, } sdim = GFC_DESCRIPTOR_RANK (source); + + /* sdim is always > 0; this lets the compiler optimize more and + avoids a warning. */ + GFC_ASSERT(sdim>0); + ssize = 1; sempty = 0; for (n = 0; n < sdim; n++) Index: generated/reshape_c8.c =================================================================== --- generated/reshape_c8.c (Revision 245760) +++ generated/reshape_c8.c (Arbeitskopie) @@ -232,6 +232,11 @@ reshape_c8 (gfc_array_c8 * const restrict ret, } sdim = GFC_DESCRIPTOR_RANK (source); + + /* sdim is always > 0; this lets the compiler optimize more and + avoids a warning. */ + GFC_ASSERT(sdim>0); + ssize = 1; sempty = 0; for (n = 0; n < sdim; n++) Index: generated/reshape_i16.c =================================================================== --- generated/reshape_i16.c (Revision 245760) +++ generated/reshape_i16.c (Arbeitskopie) @@ -232,6 +232,11 @@ reshape_16 (gfc_array_i16 * const restrict ret, } sdim = GFC_DESCRIPTOR_RANK (source); + + /* sdim is always > 0; this lets the compiler optimize more and + avoids a warning. */ + GFC_ASSERT(sdim>0); + ssize = 1; sempty = 0; for (n = 0; n < sdim; n++) Index: generated/reshape_i4.c =================================================================== --- generated/reshape_i4.c (Revision 245760) +++ generated/reshape_i4.c (Arbeitskopie) @@ -232,6 +232,11 @@ reshape_4 (gfc_array_i4 * const restrict ret, } sdim = GFC_DESCRIPTOR_RANK (source); + + /* sdim is always > 0; this lets the compiler optimize more and + avoids a warning. */ + GFC_ASSERT(sdim>0); + ssize = 1; sempty = 0; for (n = 0; n < sdim; n++) Index: generated/reshape_i8.c =================================================================== --- generated/reshape_i8.c (Revision 245760) +++ generated/reshape_i8.c (Arbeitskopie) @@ -232,6 +232,11 @@ reshape_8 (gfc_array_i8 * const restrict ret, } sdim = GFC_DESCRIPTOR_RANK (source); + + /* sdim is always > 0; this lets the compiler optimize more and + avoids a warning. */ + GFC_ASSERT(sdim>0); + ssize = 1; sempty = 0; for (n = 0; n < sdim; n++) Index: generated/reshape_r10.c =================================================================== --- generated/reshape_r10.c (Revision 245760) +++ generated/reshape_r10.c (Arbeitskopie) @@ -232,6 +232,11 @@ reshape_r10 (gfc_array_r10 * const restrict ret, } sdim = GFC_DESCRIPTOR_RANK (source); + + /* sdim is always > 0; this lets the compiler optimize more and + avoids a warning. */ + GFC_ASSERT(sdim>0); + ssize = 1; sempty = 0; for (n = 0; n < sdim; n++) Index: generated/reshape_r16.c =================================================================== --- generated/reshape_r16.c (Revision 245760) +++ generated/reshape_r16.c (Arbeitskopie) @@ -232,6 +232,11 @@ reshape_r16 (gfc_array_r16 * const restrict ret, } sdim = GFC_DESCRIPTOR_RANK (source); + + /* sdim is always > 0; this lets the compiler optimize more and + avoids a warning. */ + GFC_ASSERT(sdim>0); + ssize = 1; sempty = 0; for (n = 0; n < sdim; n++) Index: generated/reshape_r4.c =================================================================== --- generated/reshape_r4.c (Revision 245760) +++ generated/reshape_r4.c (Arbeitskopie) @@ -232,6 +232,11 @@ reshape_r4 (gfc_array_r4 * const restrict ret, } sdim = GFC_DESCRIPTOR_RANK (source); + + /* sdim is always > 0; this lets the compiler optimize more and + avoids a warning. */ + GFC_ASSERT(sdim>0); + ssize = 1; sempty = 0; for (n = 0; n < sdim; n++) Index: generated/reshape_r8.c =================================================================== --- generated/reshape_r8.c (Revision 245760) +++ generated/reshape_r8.c (Arbeitskopie) @@ -232,6 +232,11 @@ reshape_r8 (gfc_array_r8 * const restrict ret, } sdim = GFC_DESCRIPTOR_RANK (source); + + /* sdim is always > 0; this lets the compiler optimize more and + avoids a warning. */ + GFC_ASSERT(sdim>0); + ssize = 1; sempty = 0; for (n = 0; n < sdim; n++) Index: intrinsics/reshape_generic.c =================================================================== --- intrinsics/reshape_generic.c (Revision 245760) +++ intrinsics/reshape_generic.c (Arbeitskopie) @@ -158,6 +158,10 @@ reshape_internal (parray *ret, parray *source, sha source_extent = 1; sdim = GFC_DESCRIPTOR_RANK (source); + /* sdim is always > 0; this lets the compiler optimize more and + avoids a warning. */ + GFC_ASSERT(sdim>0); + for (n = 0; n < sdim; n++) { index_type se; Index: libgfortran.h =================================================================== --- libgfortran.h (Revision 245760) +++ libgfortran.h (Arbeitskopie) @@ -111,7 +111,12 @@ typedef off_t gfc_offset; #define likely(x) __builtin_expect(!!(x), 1) #define unlikely(x) __builtin_expect(!!(x), 0) +/* This macro can be used to annotate conditions which we know to + be true, so that the compiler can optimize based on the condition. */ +#define GFC_ASSERT(EXPR) \ + ((void)(__builtin_expect (!(EXPR), 0) ? __builtin_unreachable (), 0 : 0)) + /* Make sure we have ptrdiff_t. */ #ifndef HAVE_PTRDIFF_T typedef intptr_t ptrdiff_t; Index: m4/reshape.m4 =================================================================== --- m4/reshape.m4 (Revision 245760) +++ m4/reshape.m4 (Arbeitskopie) @@ -236,6 +236,11 @@ reshape_'rtype_ccode` ('rtype` * const restrict re } sdim = GFC_DESCRIPTOR_RANK (source); + + /* sdim is always > 0; this lets the compiler optimize more and + avoids a warning. */ + GFC_ASSERT(sdim>0); + ssize = 1; sempty = 0; for (n = 0; n < sdim; n++)