[llvm] [Codegen, BasicBlockSections] Avoid cloning blocks which have their machine block address taken. (PR #94296)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: Rahman Lavaee (rlavaee)

<details>
<summary>Changes</summary>

These blocks usually show up in the form of branches within inline assembly. Since it's hard to rewire them, we fully omit paths with such blocks from path cloning.

---
Full diff: https://github.com/llvm/llvm-project/pull/94296.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/BasicBlockPathCloning.cpp (+10) 
- (modified) llvm/test/CodeGen/X86/basic-block-sections-cloning-invalid.ll (+21-6) 


``````````diff
diff --git a/llvm/lib/CodeGen/BasicBlockPathCloning.cpp b/llvm/lib/CodeGen/BasicBlockPathCloning.cpp
index 901542e8507bd..19f824850607c 100644
--- a/llvm/lib/CodeGen/BasicBlockPathCloning.cpp
+++ b/llvm/lib/CodeGen/BasicBlockPathCloning.cpp
@@ -119,6 +119,16 @@ bool IsValidCloning(const MachineFunction &MF,
           return false;
         }
       }
+      if (PathBB->isMachineBlockAddressTaken()) {
+        // Avoid cloning blocks which have their address taken since we can't
+        // rewire branches to those blocks as easily (e.g., branches within
+        // inline assembly).
+        WithColor::warning()
+            << "block #" << BBID
+            << " has its machine block address taken in function "
+            << MF.getName() << "\n";
+        return false;
+      }
     }
 
     if (I != ClonePath.size() - 1 && !PathBB->empty() &&
diff --git a/llvm/test/CodeGen/X86/basic-block-sections-cloning-invalid.ll b/llvm/test/CodeGen/X86/basic-block-sections-cloning-invalid.ll
index 521ec43ef050a..c316ef9f8f260 100644
--- a/llvm/test/CodeGen/X86/basic-block-sections-cloning-invalid.ll
+++ b/llvm/test/CodeGen/X86/basic-block-sections-cloning-invalid.ll
@@ -13,8 +13,8 @@ declare void @effect(i32 zeroext)
 ; RUN: echo 'v1' > %t2
 ; RUN: echo 'f foo' >> %t2
 ; RUN: echo 'p 0 2 3' >> %t2
-; RUN: echo 'p 0 1 3' >> %t2
-; RUN: echo 'c 0 1.1 3.2 2.1 3.1 1' >> %t2
+; RUN: echo 'p 0 1 2 3' >> %t2
+; RUN: echo 'c 0 1.1 2.2 3.2 2.1 3.1 1' >> %t2
 ; RUN: llc < %s -mtriple=x86_64-pc-linux -O0 -function-sections -basic-block-sections=%t2 2> %t2.err | FileCheck %s --check-prefixes=PATH
 ; RUN: FileCheck %s --check-prefixes=WARN1 < %t2.err
 ; RUN: echo 'v1' > %t3
@@ -23,6 +23,14 @@ declare void @effect(i32 zeroext)
 ; RUN: echo 'c 0 100.1 1' >> %t3
 ; RUN: llc < %s -mtriple=x86_64-pc-linux -O0 -function-sections -basic-block-sections=%t3 2> %t3.err | FileCheck %s
 ; RUN: FileCheck %s --check-prefixes=WARN2 < %t3.err
+; RUN: echo 'v1' > %t4
+; RUN: echo 'f foo' >> %t4
+; RUN: echo 'p 1 6' >> %t4
+; RUN: echo 'c 0 1 6.1' >> %t4
+; RUN: llc < %s -mtriple=x86_64-pc-linux -O0 -function-sections -basic-block-sections=%t4 2> %t4.err | FileCheck %s
+; RUN: FileCheck %s --check-prefixes=WARN3 < %t4.err
+
+
 
 define void @foo(i1 %a, i1 %b, i1 %c, i1 %d) {
 b0:
@@ -31,23 +39,29 @@ b0:
 
 b1:                                           ; preds = %b0
   call void @effect(i32 1)
-  br i1 %b, label %b2, label %b3
+  br i1 %b, label %b2, label %b6
 
 b2:                                             ; preds = %b1
   call void @effect(i32 2)
   br label %b3
 
-b3:                                            ; preds = %b0, %b1, %b2
+b3:                                            ; preds = %b0, %b2
   call void @effect(i32 3)
   br i1 %c, label %b4, label %b5
 
 b4:                                             ; preds = %b3
   call void @effect(i32 4)
-  br i1 %d, label %b5, label %cold
+  callbr void asm sideeffect "je ${0:l}", "!i,~{dirflag},~{fpsr},~{flags}"()
+    to label %b5 [label %b6]
 
 b5:                                            ; preds = %b3, %b4
   call void @effect(i32 5)
   ret void
+
+b6:                                            ; preds = %b1, %b4
+  call void @effect(i32 6)
+  ret void
+
 cold:
   call void @effect(i32 6)                     ; preds = %b4
   ret void
@@ -59,7 +73,7 @@ cold:
 
 ; CHECK:   je .LBB0_3
 ; PATH:  # %bb.7:      # %b1
-; PATH:  # %bb.8:      # %b3
+; PATH:  # %bb.8:      # %b2
 ; PATH:    jne .LBB0_4
 ; CHECK: # %bb.1:      # %b1
 ; CHECK:   jne foo.cold
@@ -69,4 +83,5 @@ cold:
 ;; Check the warnings
 ; WARN1: warning: block #2 is not a successor of block #0 in function foo
 ; WARN2: warning: no block with id 100 in function foo
+; WARN3: warning: block #6 has its machine block address taken in function foo
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/94296