[llvm] c3b3aa2 - Fix a missing MemorySSA update in breakLoopBackedge

[Philip Reames via llvm-commits]

Author: Philip Reames
Date: 2021-09-01T16:59:01-07:00
New Revision: c3b3aa277acaccf85a49d8d74dde3f1e03a38041

URL: https://github.com/llvm/llvm-project/commit/c3b3aa277acaccf85a49d8d74dde3f1e03a38041
DIFF: https://github.com/llvm/llvm-project/commit/c3b3aa277acaccf85a49d8d74dde3f1e03a38041.diff

LOG: Fix a missing MemorySSA update in breakLoopBackedge

This is a case I'd missed in 6a8237. The odd bit here is that missing the edge removal update seems to produce MemorySSA which verifies, but is still corrupt in a way which bothers following passes. I wasn't able to reduce a single pass test case, which is why the reported test case is taken as is.

Differential Revision: https://reviews.llvm.org/D109068

Added: 
    llvm/test/Transforms/LoopDeletion/bbi-59728.ll

Modified: 
    llvm/lib/Transforms/Utils/LoopUtils.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index 36d8bc5023e48..b8f8ad579d58f 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -729,8 +729,9 @@ void llvm::breakLoopBackedge(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
       // and outer loop so the other target doesn't need to an exit
       if (L->isLoopExiting(Latch)) {
         // TODO: Generalize ConstantFoldTerminator so that it can be used
-        // here without invalidating LCSSA.  (Tricky case: header is an exit
-        // block of a preceeding sibling loop w/o dedicated exits.)
+        // here without invalidating LCSSA or MemorySSA.  (Tricky case for
+        // LCSSA: header is an exit block of a preceeding sibling loop w/o
+        // dedicated exits.)
         const unsigned ExitIdx = L->contains(BI->getSuccessor(0)) ? 1 : 0;
         BasicBlock *ExitBB = BI->getSuccessor(ExitIdx);
 
@@ -746,6 +747,8 @@ void llvm::breakLoopBackedge(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
 
         BI->eraseFromParent();
         DTU.applyUpdates({{DominatorTree::Delete, Latch, Header}});
+        if (MSSA)
+          MSSAU->applyUpdates({{DominatorTree::Delete, Latch, Header}}, DT);
         return;
       }
     }

diff  --git a/llvm/test/Transforms/LoopDeletion/bbi-59728.ll b/llvm/test/Transforms/LoopDeletion/bbi-59728.ll
new file mode 100644
index 0000000000000..7f7426fe522a5
--- /dev/null
+++ b/llvm/test/Transforms/LoopDeletion/bbi-59728.ll
@@ -0,0 +1,27 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt %s -verify-memoryssa -passes='loop-mssa(loop-deletion,loop-simplifycfg)' -S | FileCheck %s
+
+; This is a case where we failed to update memory SSA correctly in
+; loop-deletion which escapes local verification, but causes a crash
+; in loop-simplifycfg.
+define void @func_45() {
+; CHECK-LABEL: @func_45(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_BODY45:%.*]]
+; CHECK:       for.body45:
+; CHECK-NEXT:    store i32 433429641, i32* undef, align 1
+; CHECK-NEXT:    br label [[FOR_BODY45]]
+;
+entry:
+  br label %for.body45
+
+for.body45:                                       ; preds = %for.end72, %entry
+  br label %for.body48
+
+for.body48:                                       ; preds = %for.body48, %for.body45
+  store i32 433429641, i32* undef, align 1
+  br i1 undef, label %for.body48, label %for.end72
+
+for.end72:                                        ; preds = %for.body48
+  br label %for.body45
+}