[PATCH] D103181: [SimplifyCFG] Don't use phis() while deleting instructions

[Heejin Ahn via Phabricator via llvm-commits]

aheejin created this revision.
aheejin added reviewers: lebedev.ri, dschuff.
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We are deleting `phi` nodes within the for loop, so we can't use
`phis()` to iterate `phi` nodes.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D103181

Files:
  llvm/lib/Transforms/Utils/SimplifyCFG.cpp
  llvm/test/Transforms/SimplifyCFG/cleanup-phis.ll


Index: llvm/test/Transforms/SimplifyCFG/cleanup-phis.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/SimplifyCFG/cleanup-phis.ll
@@ -0,0 +1,43 @@
+; RUN: opt < %s -simplifycfg -S | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown"
+
+; This is a regression test for a bug in which we used phis() in a for loop
+; while deleting phi nodes.
+
+define void @cleanup_phis() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+bb0:
+  invoke void @foo()
+          to label %bb1 unwind label %ehcleanup
+
+bb1:                                              ; preds = %bb0
+  invoke void @foo()
+          to label %invoke.cont unwind label %ehcleanup
+
+invoke.cont:                                      ; preds = %bb1
+  ret void
+
+ehcleanup:                                       ; preds = %bb1, %bb0
+  %phi0 = phi i32 [ 0, %bb0 ], [ 1, %bb1 ]
+  %phi1 = phi i32 [ 2, %bb0 ], [ 3, %bb1 ]
+  %0 = cleanuppad within none []
+  cleanupret from %0 unwind label %catchswitch
+
+; These two phi nodes were originally in ehcleanup. Both phi nodes should be
+; correctly copied to this catchswitch BB.
+; CHECK: catchswitch:
+; CHECK-NEXT:  %phi0 = phi i32 [ 0, %bb0 ], [ 1, %bb1 ]
+; CHECK-NEXT:  %phi1 = phi i32 [ 2, %bb0 ], [ 3, %bb1 ]
+catchswitch:                                      ; preds = %ehcleanup
+  %1 = catchswitch within none [label %catch] unwind to caller
+
+catch:                                            ; preds = %catchswitch
+  %2 = catchpad within %1 [i8* null]
+  call void @bar(i32 %phi0, i32 %phi1)
+  unreachable
+}
+
+declare void @foo()
+declare void @bar(i32, i32)
+declare i32 @__gxx_wasm_personality_v0(...)
Index: llvm/lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -4500,10 +4500,12 @@
 
     // Sink any remaining PHI nodes directly into UnwindDest.
     Instruction *InsertPt = DestEHPad;
-    for (PHINode &PN : BB->phis()) {
+    for (auto I = BB->begin(), IE = BB->getFirstNonPHI()->getIterator();
+         I != IE;) {
       // The iterator must be incremented here because the instructions are
       // being moved to another block.
-      if (PN.use_empty() || !PN.isUsedOutsideOfBlock(BB))
+      PHINode *PN = cast<PHINode>(I++);
+      if (PN->use_empty() || !PN->isUsedOutsideOfBlock(BB))
         // If the PHI node has no uses or all of its uses are in this basic
         // block (meaning they are debug or lifetime intrinsics), just leave
         // it.  It will be erased when we erase BB below.
@@ -4515,11 +4517,11 @@
       // BB.  In this case, the PHI value must reference itself.
       for (auto *pred : predecessors(UnwindDest))
         if (pred != BB)
-          PN.addIncoming(&PN, pred);
-      PN.moveBefore(InsertPt);
+          PN->addIncoming(PN, pred);
+      PN->moveBefore(InsertPt);
       // Also, add a dummy incoming value for the original BB itself,
       // so that the PHI is well-formed until we drop said predecessor.
-      PN.addIncoming(UndefValue::get(PN.getType()), BB);
+      PN->addIncoming(UndefValue::get(PN->getType()), BB);
     }
   }
 


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