[llvm] d0ec03a - Revert "[BasicBlockSections] avoid insertting redundant branch to fall through blocks"

[Rahman Lavaee via llvm-commits]

Author: Rahman Lavaee
Date: 2023-08-23T01:09:13Z
New Revision: d0ec03a384a5aa73a51735e897fecac0e0ad13b1

URL: https://github.com/llvm/llvm-project/commit/d0ec03a384a5aa73a51735e897fecac0e0ad13b1
DIFF: https://github.com/llvm/llvm-project/commit/d0ec03a384a5aa73a51735e897fecac0e0ad13b1.diff

LOG: Revert "[BasicBlockSections] avoid insertting redundant branch to fall through blocks"

This reverts commit ab53109166c0345a79cbd6939cf7bc764a982856 which was
commited by mistake.

Added: 
    

Modified: 
    llvm/lib/CodeGen/BasicBlockSections.cpp

Removed: 
    llvm/test/CodeGen/X86/basic-block-sections-avoids-redundant-br.ll


################################################################################
diff  --git a/llvm/lib/CodeGen/BasicBlockSections.cpp b/llvm/lib/CodeGen/BasicBlockSections.cpp
index 4ebff65a2daf7f..33e70b160d9212 100644
--- a/llvm/lib/CodeGen/BasicBlockSections.cpp
+++ b/llvm/lib/CodeGen/BasicBlockSections.cpp
@@ -134,14 +134,6 @@ INITIALIZE_PASS_END(BasicBlockSections, "bbsections-prepare",
                     "into clusters of basic blocks.",
                     false, false)
 
-// Returns whether the given basic block has an unconditional branch.
-bool hasUnconditionalBranch(const MachineBasicBlock &MBB) {
-  if (MBB.terminators().empty())
-    return false;
-  const MachineInstr &Terminator = *(--MBB.terminators().end());
-  return Terminator.isUnconditionalBranch();
-}
-
 // This function updates and optimizes the branching instructions of every basic
 // block in a given function to account for changes in the layout.
 static void
@@ -153,14 +145,12 @@ updateBranches(MachineFunction &MF,
     auto NextMBBI = std::next(MBB.getIterator());
     auto *FTMBB = PreLayoutFallThroughs[MBB.getNumber()];
     // If this block had a fallthrough before we need an explicit unconditional
-    // branch to that block if either one of these two conditions hold and the
-    // block doesn't currently have an unconditional branch.
+    // branch to that block if either
     //     1- the block ends a section, which means its next block may be
     //        reorderd by the linker, or
     //     2- the fallthrough block is not adjacent to the block in the new
     //        order.
-    if (FTMBB && (MBB.isEndSection() || &*NextMBBI != FTMBB) &&
-        !hasUnconditionalBranch(MBB))
+    if (FTMBB && (MBB.isEndSection() || &*NextMBBI != FTMBB))
       TII->insertUnconditionalBranch(MBB, FTMBB, MBB.findBranchDebugLoc());
 
     // We do not optimize branches for machine basic blocks ending sections, as

diff  --git a/llvm/test/CodeGen/X86/basic-block-sections-avoids-redundant-br.ll b/llvm/test/CodeGen/X86/basic-block-sections-avoids-redundant-br.ll
deleted file mode 100644
index 6571e273795284..00000000000000
--- a/llvm/test/CodeGen/X86/basic-block-sections-avoids-redundant-br.ll
+++ /dev/null
@@ -1,56 +0,0 @@
-; Tests that basic block sections avoids inserting an unconditional branch when a basic block
-; already has an unconditional branch to its fallthrough block.
-; RUN: llc < %s -mtriple=x86_64 -basic-block-sections=all -O0 | FileCheck %s
-; This test case is generated from code:
-; int
-; mapping (int len)
-; {
-;   switch (len)
-;   {
-;     case 7: return 333;
-;     default:
-;       goto unknown;
-;   }
-; unknown:
-;   return 0;
-; }
-; clang -O0 -fbasic-block-sections=all test.c
-
-; Function Attrs: noinline nounwind optnone uwtable
-define dso_local i32 @mapping(i32 noundef %len) {
-entry:
-  %retval = alloca i32, align 4
-  %len.addr = alloca i32, align 4
-  store i32 %len, ptr %len.addr, align 4
-  %0 = load i32, ptr %len.addr, align 4
-  switch i32 %0, label %sw.default [
-    i32 7, label %sw.bb
-  ]
-
-sw.bb:                                            ; preds = %entry
-  store i32 333, ptr %retval, align 4
-  br label %return
-
-sw.default:                                       ; preds = %entry
-  br label %unknown
-
-unknown:                                          ; preds = %sw.default
-  store i32 0, ptr %retval, align 4
-  br label %return
-
-return:                                           ; preds = %unknown, %sw.bb
-  %1 = load i32, ptr %retval, align 4
-  ret i32 %1
-}
-
-; CHECK: mapping:
-; CHECK-NEXT: .cfi_startproc
-; CHECK-NEXT: # %bb.0: # %entry
-; CHECK-NEXT: movl {{.*}}
-; CHECK-NEXT: movl {{.*}}
-; CHECK-NEXT: subl {{.*}}
-; CHECK-NEXT: jne	mapping.__part.2
-; CHECK-NEXT: jmp	mapping.__part.1
-; CHECK-NOT:  jmp
-; CHECK: mapping.__part.1:
-; CHECK: mapping.__part.2: