[ELF] Refine warning condition for memory region assignment for non-allocatable section

The warning "ignoring memory region assignment for non-allocatable section"  should be generated under the following conditions:

* sections without SHF_ALLOC attribute and,
* presence of input sections or data commands (ByteCommand)

The goal of the change is to reduce spurious warnings that are generated for some output sections that have no input section.

Reviewed By: MaskRay, peter.smith

Differential Revision: https://reviews.llvm.org/D151802

Author: Andreu Carminati

lld/ELF/LinkerScript.cpp

@@ -909,7 +909,12 @@ std::pair<MemoryRegion *, MemoryRegion *>
 LinkerScript::findMemoryRegion(OutputSection *sec, MemoryRegion *hint) {
   // Non-allocatable sections are not part of the process image.
   if (!(sec->flags & SHF_ALLOC)) {
-    if (!sec->memoryRegionName.empty())
+    bool hasInputOrByteCommand =
+        sec->hasInputSections ||
+        llvm::any_of(sec->commands, [](SectionCommand *comm) {
+          return ByteCommand::classof(comm);
+        });
+    if (!sec->memoryRegionName.empty() && hasInputOrByteCommand)
       warn("ignoring memory region assignment for non-allocatable section '" +
            sec->name + "'");
     return {nullptr, nullptr};

lld/test/ELF/linkerscript/memory-nonalloc-no-warn.test

@@ -0,0 +1,59 @@
+# REQUIRES: x86
+
+# RUN: split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/a.s -o %t/a.o
+
+## Check if the linker can generate the final file, containing all non-empty sections,
+## without warnings for .intvec0_out, .intvec1_out1, .intvec2_out, because their
+## input sections are empty. Althoung, the linker must generate a warning for the
+## first ".nonalloc" section and the second .dat, as expected.
+
+# RUN: ld.lld %t/a.o -T %t/a.lds -o %t/a.elf 2>&1 | FileCheck %s --check-prefix=WARN --implicit-check-not=warning:
+
+# WARN: warning: ignoring memory region assignment for non-allocatable section '.nonalloc'
+# WARN: warning: ignoring memory region assignment for non-allocatable section '.dat'
+
+## The output file must include all sections.
+# RUN: llvm-readelf -S %t/a.elf | FileCheck %s
+
+# CHECK:      There are 12 section headers, starting at offset 0x2140:
+# CHECK:      [Nr] Name         Type      Address          Off    Size   ES Flg Lk Inf Al
+# CHECK-NEXT: [ 0]              NULL      0000000000000000 000000 000000 00     0  0   0
+# CHECK-NEXT: [ 1] .nonalloc    PROGBITS  0000000000000000 001064 001000 00 W   0  0   1
+# CHECK-NEXT: [ 2] .comment     PROGBITS  0000000000000000 {{.*}} {{.*}} 01 MS  0  0   1
+# CHECK-NEXT: [ 3] .symtab      SYMTAB    0000000000000000 {{.*}} {{.*}} 18     5  1   8
+# CHECK-NEXT: [ 4] .shstrtab    STRTAB    0000000000000000 {{.*}} {{.*}} 00     0  0   1
+# CHECK-NEXT: [ 5] .strtab      STRTAB    0000000000000000 {{.*}} {{.*}} 00     0  0   1
+# CHECK-NEXT: [ 6] .dat         PROGBITS  0000000000000000 002137 000004 00 W   0  0   1
+# CHECK-NEXT: [ 7] .intvec0_out PROGBITS  0000000000000000 00213b 000000 00 W   0  0   1
+# CHECK-NEXT: [ 8] .intvec1_out PROGBITS  0000000000000000 00213b 000000 00 W   0  0   1
+# CHECK-NEXT: [ 9] .intvec2_out PROGBITS  0000000000000000 00213b 000000 00 W   0  0   1
+# CHECK-NEXT: [10] .intvec3_out PROGBITS  00000000803fe060 001060 000004 00 AX  0  0   1
+# CHECK-NEXT: [11] .text        PROGBITS  00000000803fe064 001064 000000 00 AX  0  0   4
+
+
+#--- a.s
+.global _start
+.text
+_start:
+.section .nonalloc,"w"
+.zero 0x1000
+.section .intvec3,"ax",@progbits
+.long 1
+
+#--- a.lds
+MEMORY {
+  MEM1 : ORIGIN = 0x10000000, LENGTH = 1M
+  MEM2 (rx) : ORIGIN = 0x80000000, LENGTH = 4M
+}
+
+VEC_START = 0x803FE000;
+
+SECTIONS {
+ .nonalloc : { *(.nonalloc) } > MEM
+ .dat : { LONG(0); } > MEM1
+ .intvec0_out (VEC_START + 0x0000) : {KEEP (*(.intvec1)) } > MEM2
+ .intvec1_out (VEC_START + 0x0020) : {KEEP (*(.intvec1)) } > MEM2
+ .intvec2_out (VEC_START + 0x0040) : {KEEP (*(.intvec2)) } > MEM2
+ .intvec3_out (VEC_START + 0x0060) : {KEEP (*(.intvec3)) } > MEM2
+}