[llvm] 384996f - [IndVarSimplify] Fix Modified status when handling dead PHI nodes

[David Stenberg via llvm-commits]

Author: David Stenberg
Date: 2020-11-26T14:28:21+01:00
New Revision: 384996f9e18ff3b7fa35b2083bf352c64b05c7bc

URL: https://github.com/llvm/llvm-project/commit/384996f9e18ff3b7fa35b2083bf352c64b05c7bc
DIFF: https://github.com/llvm/llvm-project/commit/384996f9e18ff3b7fa35b2083bf352c64b05c7bc.diff

LOG: [IndVarSimplify] Fix Modified status when handling dead PHI nodes

When bailing out in rewriteLoopExitValues() you could be left with PHI
nodes in the DeadInsts vector. Those would be not handled by the use of
RecursivelyDeleteTriviallyDeadInstructions() in IndVarSimplify. This
resulted in the IndVarSimplify pass returning an incorrect modified
status. This was caught by the expensive check introduced in D86589.

This patches changes IndVarSimplify so that it deletes those PHI nodes,
using RecursivelyDeleteDeadPHINode().

This fixes PR47486.

Reviewed By: mkazantsev

Differential Revision: https://reviews.llvm.org/D91153

Added: 
    llvm/test/Transforms/IndVarSimplify/rewrite-loop-exit-values-phi.ll

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index 5ff4c9ad18f46..ab40a9e533de2 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -1869,11 +1869,15 @@ bool IndVarSimplify::run(Loop *L) {
 
   // Now that we're done iterating through lists, clean up any instructions
   // which are now dead.
-  while (!DeadInsts.empty())
-    if (Instruction *Inst =
-            dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val()))
+  while (!DeadInsts.empty()) {
+    Value *V = DeadInsts.pop_back_val();
+
+    if (PHINode *PHI = dyn_cast_or_null<PHINode>(V))
+      Changed |= RecursivelyDeleteDeadPHINode(PHI, TLI, MSSAU.get());
+    else if (Instruction *Inst = dyn_cast_or_null<Instruction>(V))
       Changed |=
           RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI, MSSAU.get());
+  }
 
   // The Rewriter may not be used from this point on.
 

diff  --git a/llvm/test/Transforms/IndVarSimplify/rewrite-loop-exit-values-phi.ll b/llvm/test/Transforms/IndVarSimplify/rewrite-loop-exit-values-phi.ll
new file mode 100644
index 0000000000000..21eb9892f9c95
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/rewrite-loop-exit-values-phi.ll
@@ -0,0 +1,51 @@
+; RUN: opt -indvars -S %s -o - | FileCheck %s
+
+; When bailing out in rewriteLoopExitValues() you would be left with a PHI node
+; that was not deleted, and the IndVar pass would return an incorrect modified
+; status. This was caught by the expensive check introduced in D86589.
+
+; CHECK-LABEL: header:
+; CHECK-NEXT: %idx = phi i64 [ %idx.next, %latch ], [ undef, %entry ]
+; CHECK-NEXT: %cond = icmp sgt i64 %n, %idx
+; CHECK-NEXT: br i1 %cond, label %end, label %inner.preheader
+
+; CHECK-LABEL: latch:
+; CHECK-NEXT: %idx.next = add nsw i64 %idx, -1
+; CHECK-NEXT: br label %header
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+ at ptr = external global i64
+
+define dso_local void @hoge() local_unnamed_addr {
+entry:                                            ; preds = %entry
+  %n = sdiv exact i64 undef, 40
+  br label %header
+
+header:                                           ; preds = %latch, %entry
+  %idx = phi i64 [ %idx.next, %latch ], [ undef, %entry ]
+  %cond = icmp sgt i64 %n, %idx
+  br i1 %cond, label %end, label %inner
+
+inner:                                            ; preds = %inner, %header
+  %i = phi i64 [ %i.next, %inner ], [ 0, %header ]
+  %j = phi i64 [ %j.next, %inner ], [ %n, %header ]
+  %i.next = add nsw i64 %i, 1
+  %j.next = add nsw i64 %j, 1
+  store i64 undef, i64* @ptr
+  %cond1 = icmp slt i64 %j, %idx
+  br i1 %cond1, label %inner, label %inner_exit
+
+inner_exit:                                       ; preds = %inner
+  %indvar = phi i64 [ %i.next, %inner ]
+  %indvar_use = add i64 %indvar, 1
+  br label %latch
+
+latch:                                            ; preds = %inner_exit
+  %idx.next = add nsw i64 %idx, -1
+  br label %header
+
+end:                                              ; preds = %header
+  ret void
+}