[yaml2obj] - Change how p_offset is calculated when creating segments. NFCI.

[grimar]

Summary

This depends on D78361 and simplifies the computation of the p_offset.

[MaskRay]

LGTM.

[jhenderson]

LGTM.

llvm/lib/ObjectYAML/ELFEmitter.cpp

for (auto &YamlPhdr : Doc.ProgramHeaders) {
     Elf_Phdr &PHeader = PHeaders[PhdrIdx++];
     std::vector<Fragment> Fragments = getPhdrFragments(YamlPhdr, SHeaders);
     if (!llvm::is_sorted(Fragments, [](const Fragment &A, const Fragment &B) {
           return A.Offset < B.Offset;
         }))
       reportError("sections in the program header with index " +
                   Twine(PhdrIdx) + " are not sorted by their file offset");
 
-    if (YamlPhdr.Offset) {
+    if (YamlPhdr.Offset)
       PHeader.p_offset = *YamlPhdr.Offset;
-    } else {
-      if (YamlPhdr.Sections.size())
-        PHeader.p_offset = UINT32_MAX;
-      else
-        PHeader.p_offset = 0;
+    else if (!Fragments.empty())
+      PHeader.p_offset = Fragments.front().Offset;
 
-      // Find the minimum offset for the program header.
-      for (const Fragment &F : Fragments)
-        PHeader.p_offset = std::min((uint64_t)PHeader.p_offset, F.Offset);
-    }
-
     // Find the maximum offset of the end of a section in order to set p_filesz
     // and p_memsz. When setting p_filesz, trailing SHT_NOBITS sections are not
     // counted.
     uint64_t FileOffset = PHeader.p_offset, MemOffset = PHeader.p_offset;
     for (const Fragment &F : Fragments) {
       uint64_t End = F.Offset + F.Size;
       MemOffset = std::max(MemOffset, End);