Do not remove empty basic blocks which have address taken.

[rlavaee]

This PR replaces isMachineBlockAddressTaken by hasAddressTaken to include blocks which have their IR address taken as well. These blocks are also not removable since their predecessors' terminators do not directly point to the block.

[llvmbot]

@llvm/pr-subscribers-backend-x86

Changes

This PR replaces isMachineBlockAddressTaken by hasAddressTaken to include blocks which have their IR address taken as well. These blocks are also not removable since their predecessors' terminators do not directly point to the block.

---

Full diff: https://github.com/llvm/llvm-project/pull/67740.diff

2 Files Affected:

• (modified) llvm/lib/CodeGen/GCEmptyBasicBlocks.cpp (+1-1)
• (modified) llvm/test/CodeGen/X86/gc-empty-basic-blocks.ll (+29-5)

diff --git a/llvm/lib/CodeGen/GCEmptyBasicBlocks.cpp b/llvm/lib/CodeGen/GCEmptyBasicBlocks.cpp
index e261531eb014052..598be26e40c8e9a 100644
--- a/llvm/lib/CodeGen/GCEmptyBasicBlocks.cpp
+++ b/llvm/lib/CodeGen/GCEmptyBasicBlocks.cpp
@@ -58,7 +58,7 @@ bool GCEmptyBasicBlocks::runOnMachineFunction(MachineFunction &MF) {
     // TODO If a block is an eh pad, or it has address taken, we don't remove
     // it. Removing such blocks is possible, but it probably requires a more
     // complex logic.
-    if (MBB->isEHPad() || MBB->isMachineBlockAddressTaken())
+    if (MBB->isEHPad() || MBB->hasAddressTaken())
       continue;
     // Skip blocks with real code.
     bool HasAnyRealCode = llvm::any_of(*MBB, [](const MachineInstr &MI) {
diff --git a/llvm/test/CodeGen/X86/gc-empty-basic-blocks.ll b/llvm/test/CodeGen/X86/gc-empty-basic-blocks.ll
index f737e43d3b816af..bacdad07a14a51e 100644
--- a/llvm/test/CodeGen/X86/gc-empty-basic-blocks.ll
+++ b/llvm/test/CodeGen/X86/gc-empty-basic-blocks.ll
@@ -1,6 +1,8 @@
-;; This test verifies that -gc-empty-basic-blocks removes empty blocks.
+;; This test verifies that -gc-empty-basic-blocks removes regular empty blocks
+;; but does not remove empty blocks which have their address taken.
 ; RUN: llc < %s -mtriple=x86_64 -O0 -gc-empty-basic-blocks | FileCheck %s
 
+;; This function has a regular empty block.
 define void @foo(i1 zeroext %0) nounwind {
   br i1 %0, label %2, label %empty_block
 
@@ -10,7 +12,7 @@ define void @foo(i1 zeroext %0) nounwind {
 ; CHECK-NEXT:    jmp .LBB0_3
 
 2:                                               ; preds = %1
-  %3 = call i32 @bar()
+  %3 = call i32 @baz()
   br label %4
 
 ; CHECK-LABEL: .LBB0_1:
@@ -19,8 +21,8 @@ define void @foo(i1 zeroext %0) nounwind {
 empty_block:                                     ; preds = %1
   unreachable
 
-; CHECK-NOT: %empty_block
-; CHECK-NOT: .LBB0_2
+; CHECK-NOT:     %empty_block
+; CHECK-NOT:   .LBB0_2
 
 4:                                               ; preds = %2, %empty_block
   ret void
@@ -30,4 +32,26 @@ empty_block:                                     ; preds = %1
 
 }
 
-declare i32 @bar()
+;; This function has an empty block which has its address taken.
+define void @bar(i1 zeroext %0) nounwind {
+entry:
+  %1 = select i1 %0, ptr blockaddress(@bar, %empty_block), ptr blockaddress(@bar, %bb2) ; <ptr> [#uses=1]
+  indirectbr ptr %1, [label %empty_block, label %bb2]
+
+; CHECK-LABEL: bar:
+; CHECK-LABEL: %bb.0:
+; CHECK:         jmpq *%rax
+
+empty_block:                                                ; preds = %entry
+  unreachable
+
+; CHECK-LABEL: .LBB1_1: # %empty_block
+
+bb2:                                                ; preds = %entry
+  %2 = call i32 @baz()
+  ret void
+; CHECK-LABEL: .LBB1_2:
+; CHECK-NEXT:    callq   baz
+}
+
+declare i32 @baz()