[llvm] e9716c6 - [StructurizeCFG] Remove imposible case and replace by assert

[Juan Manuel MARTINEZ CAAMAÑO via llvm-commits]

Author: Juan Manuel MARTINEZ CAAMAÑO
Date: 2022-09-29T08:27:49Z
New Revision: e9716c64ec065693d53502b84b8a74190b691248

URL: https://github.com/llvm/llvm-project/commit/e9716c64ec065693d53502b84b8a74190b691248
DIFF: https://github.com/llvm/llvm-project/commit/e9716c64ec065693d53502b84b8a74190b691248.diff

LOG: [StructurizeCFG] Remove imposible case and replace by assert

In addition, replace outdated XFAIL test by a new one.

Differential Revision: https://reviews.llvm.org/D134439

Added: 
    llvm/test/Transforms/StructurizeCFG/infinite-loop.ll

Modified: 
    llvm/lib/Transforms/Scalar/StructurizeCFG.cpp

Removed: 
    llvm/test/Transforms/StructurizeCFG/no-branch-to-entry.ll


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/StructurizeCFG.cpp b/llvm/lib/Transforms/Scalar/StructurizeCFG.cpp
index b8ad09e037e70..9e2fb6a27f5a4 100644
--- a/llvm/lib/Transforms/Scalar/StructurizeCFG.cpp
+++ b/llvm/lib/Transforms/Scalar/StructurizeCFG.cpp
@@ -972,20 +972,7 @@ void StructurizeCFG::handleLoops(bool ExitUseAllowed,
     handleLoops(false, LoopEnd);
   }
 
-  // If the start of the loop is the entry block, we can't branch to it so
-  // insert a new dummy entry block.
-  Function *LoopFunc = LoopStart->getParent();
-  if (LoopStart == &LoopFunc->getEntryBlock()) {
-    LoopStart->setName("entry.orig");
-
-    BasicBlock *NewEntry =
-      BasicBlock::Create(LoopStart->getContext(),
-                         "entry",
-                         LoopFunc,
-                         LoopStart);
-    BranchInst::Create(LoopStart, NewEntry);
-    DT->setNewRoot(NewEntry);
-  }
+  assert(LoopStart != &LoopStart->getParent()->getEntryBlock());
 
   // Create an extra loop end node
   LoopEnd = needPrefix(false);

diff  --git a/llvm/test/Transforms/StructurizeCFG/infinite-loop.ll b/llvm/test/Transforms/StructurizeCFG/infinite-loop.ll
new file mode 100644
index 0000000000000..30ffb5602ae4c
--- /dev/null
+++ b/llvm/test/Transforms/StructurizeCFG/infinite-loop.ll
@@ -0,0 +1,59 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -o - -structurizecfg -verify-dom-info < %s | FileCheck %s
+
+; This test hits a limitation in StructurizeCFG: it doesn't handle infinite-loops.
+; In this case, the IR remains unchanged.
+
+define void @infinite_loop_false(i32 addrspace(1)* %out, i1 %cond) {
+; CHECK-LABEL: @infinite_loop_false(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[COND:%.*]], label [[FOR_END:%.*]], label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    store volatile i32 999, i32 addrspace(1)* [[OUT:%.*]], align 4
+; CHECK-NEXT:    br label [[FOR_BODY]]
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br i1 %cond, label %for.end, label %for.body
+
+for.body:
+  store volatile i32 999, i32 addrspace(1)* %out, align 4
+  br label %for.body
+
+for.end:
+  ret void
+}
+
+define void @infinite_loop_on_branch(i32 addrspace(1)* %out, i1 %cond) {
+; CHECK-LABEL: @infinite_loop_on_branch(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[COND:%.*]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    store volatile i32 999, i32 addrspace(1)* [[OUT:%.*]], align 4
+; CHECK-NEXT:    br label [[FOR_BODY]]
+; CHECK:       if.else:
+; CHECK-NEXT:    store volatile i32 111, i32 addrspace(1)* [[OUT]], align 4
+; CHECK-NEXT:    br label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br i1 %cond, label %if.then, label %if.else
+
+if.then:
+  br label %for.body
+
+for.body:
+  store volatile i32 999, i32 addrspace(1)* %out, align 4
+  br label %for.body
+
+if.else:
+  store volatile i32 111, i32 addrspace(1)* %out, align 4
+  br label %exit
+
+exit:
+  ret void
+}

diff  --git a/llvm/test/Transforms/StructurizeCFG/no-branch-to-entry.ll b/llvm/test/Transforms/StructurizeCFG/no-branch-to-entry.ll
deleted file mode 100644
index b0897ee6c8596..0000000000000
--- a/llvm/test/Transforms/StructurizeCFG/no-branch-to-entry.ll
+++ /dev/null
@@ -1,38 +0,0 @@
-; XFAIL: *
-
-; This test used to generate a region that caused it to delete the entry block,
-; but it does not anymore after the changes to handling of infinite loops in the
-; PostDominatorTree.
-; TODO: This should be either replaced with another IR or deleted completely.
-
-; RUN: opt -S -o - -structurizecfg -verify-dom-info < %s | FileCheck %s
-
-; CHECK-LABEL: @no_branch_to_entry_undef(
-; CHECK: entry:
-; CHECK-NEXT: br label %entry.orig
-define void @no_branch_to_entry_undef(i32 addrspace(1)* %out) {
-entry:
-  br i1 undef, label %for.end, label %for.body
-
-for.body:                                         ; preds = %entry, %for.body
-  store i32 999, i32 addrspace(1)* %out, align 4
-  br label %for.body
-
-for.end:                                          ; preds = %Flow
-  ret void
-}
-
-; CHECK-LABEL: @no_branch_to_entry_true(
-; CHECK: entry:
-; CHECK-NEXT: br label %entry.orig
-define void @no_branch_to_entry_true(i32 addrspace(1)* %out) {
-entry:
-  br i1 true, label %for.end, label %for.body
-
-for.body:                                         ; preds = %entry, %for.body
-  store i32 999, i32 addrspace(1)* %out, align 4
-  br label %for.body
-
-for.end:                                          ; preds = %Flow
-  ret void
-}