[PATCH] D140831: Fix a phase-ordering problem in SimplifyCFG.

[Owen Anderson via Phabricator via llvm-commits]

resistor updated this revision to Diff 486097.
resistor added a comment.

Restart case iteration when we fold the switch condition.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D140831/new/

https://reviews.llvm.org/D140831

Files:
  llvm/lib/Transforms/Utils/Local.cpp
  llvm/test/Transforms/SimplifyCFG/switch-simplify-crash2.ll


Index: llvm/test/Transforms/SimplifyCFG/switch-simplify-crash2.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/SimplifyCFG/switch-simplify-crash2.ll
@@ -0,0 +1,27 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -passes="simplifycfg<forward-switch-cond;no-keep-loops>" < %s | FileCheck %s
+
+define i8 @test() {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP2:%.*]]
+; CHECK:       loop2:
+; CHECK-NEXT:    br label [[LOOP2]]
+;
+entry:
+  br label %loop
+
+loop:
+  %phi1 = phi i8 [ 0, %entry ], [ %phi2, %loop2 ]
+  br label %loop2
+
+loop2:
+  %phi2 = phi i8 [ %phi1, %loop ], [ 0, %loop2 ]
+  switch i8 %phi2, label %loop [
+  i8 0, label %loop2
+  i8 1, label %exit
+  ]
+
+exit:
+  ret i8 0
+}
Index: llvm/lib/Transforms/Utils/Local.cpp
===================================================================
--- llvm/lib/Transforms/Utils/Local.cpp
+++ llvm/lib/Transforms/Utils/Local.cpp
@@ -237,6 +237,15 @@
         DefaultDest->removePredecessor(ParentBB);
         i = SI->removeCase(i);
         e = SI->case_end();
+
+        // Removing this case may have made the condition constant. In that
+        // case, update CI and restart iteration through the cases.
+        ConstantInt* NewCI = dyn_cast<ConstantInt>(SI->getCondition());
+        if (NewCI) {
+          CI = NewCI;
+          i = SI->case_begin();
+        }
+
         Changed = true;
         continue;
       }


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