[cfi] Support explicit sections for functions in cfi-icall.

[eugenis]

Summary

Allow explicit section for indirectly called functions in cfi-icall.
Jumptables for functions in the same type class must be contiguous, so they
always go to the default text section.

Fixes PR25079.

[pcc]

Please add "Fixes PR25079." to commit message.

lib/Transforms/IPO/LowerBitSets.cpp

642

Instead of removing this check, please change it to allow functions but not global variables.

[eugenis]

lib/Transforms/IPO/LowerBitSets.cpp

642

Good point, done.

[pcc]

LGTM

[eugenis]

Thanks!
r266486

lib/Transforms/IPO/LowerBitSets.cpp

void LowerBitSets::verifyBitSetMDNode(MDNode *Op) {
   if (!OpConstMD)
     report_fatal_error("Bit set element must be a constant");
   auto OpGlobal = dyn_cast<GlobalObject>(OpConstMD->getValue());
   if (!OpGlobal)
     return;
 
   if (OpGlobal->isThreadLocal())
     report_fatal_error("Bit set element may not be thread-local");
-  if (OpGlobal->hasSection())
-    report_fatal_error("Bit set element may not have an explicit section");
+  if (isa<GlobalVariable>(OpGlobal) && OpGlobal->hasSection())
+    report_fatal_error(
+        "Bit set global var element may not have an explicit section");
 
   if (isa<GlobalVariable>(OpGlobal) && OpGlobal->isDeclarationForLinker())
     report_fatal_error("Bit set global var element must be a definition");
 
   auto OffsetConstMD = dyn_cast<ConstantAsMetadata>(Op->getOperand(2));
   if (!OffsetConstMD)
     report_fatal_error("Bit set element offset must be a constant");
   auto OffsetInt = dyn_cast<ConstantInt>(OffsetConstMD->getValue());

test/Transforms/LowerBitSets/section.ll

+; Test that functions with "section" attribute are accepted, and jumptables are
+; emitted in ".text".
+
+; RUN: opt -S -lowerbitsets < %s | FileCheck %s
+
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK: @[[A:.*]] = private constant {{.*}} section ".text"
+; CHECK: @f = alias void (), bitcast ({{.*}}* @[[A]] to void ()*)
+; CHECK: define private void {{.*}} section "xxx"
+
+define void @f() section "xxx" {
+entry:
+  ret void
+}
+
+define i1 @g() {
+entry:
+  %0 = call i1 @llvm.bitset.test(i8* bitcast (void ()* @f to i8*), metadata !"_ZTSFvE")
+  ret i1 %0
+}
+
+declare i1 @llvm.bitset.test(i8*, metadata) nounwind readnone
+
+!llvm.bitsets = !{!0}
+!0 = !{!"_ZTSFvE", void ()* @f, i64 0}