[PATCH] D46275: [JumpThreading] ComputeValueKnownInPredecessors only handles the case when phi is on lhs of a comparison op

[Wei Mi via Phabricator via llvm-commits]

wmi updated this revision to Diff 144648.
wmi added a comment.

update the patch to fix a bug found in llvm bootstrap.


Repository:
  rL LLVM

https://reviews.llvm.org/D46275

Files:
  lib/Transforms/Scalar/JumpThreading.cpp
  test/Other/pr32085.ll
  test/Transforms/JumpThreading/phi-known.ll


Index: test/Transforms/JumpThreading/phi-known.ll
===================================================================
--- test/Transforms/JumpThreading/phi-known.ll
+++ test/Transforms/JumpThreading/phi-known.ll
@@ -64,3 +64,41 @@
   ret void
 }
 
+; The eq predicate is always true if we go through the path from
+; L1 to L3, no matter the phi result %t5 is on the lhs or rhs of
+; the predicate.
+declare void @goo()
+declare void @hoo()
+
+define void @test3(i32 %m, i32** %t1) {
+L1:
+  %t0 = add i32 %m, 7
+  %t2 = load i32*, i32** %t1, align 8
+; CHECK-LABEL: @test3
+; CHECK: %t3 = icmp eq i32* %t2, null
+; CHECK: br i1 %t3, label %[[LABEL2:.*]], label %[[LABEL1:.*]]
+
+  %t3 = icmp eq i32* %t2, null
+  br i1 %t3, label %L3, label %L2
+
+; CHECK: [[LABEL1]]:
+; CHECK-NEXT: %t4 = load i32, i32* %t2, align 4
+L2:
+  %t4 = load i32, i32* %t2, align 4
+  br label %L3
+
+L3:
+  %t5 = phi i32 [ %t0, %L1 ], [ %t4, %L2 ]
+  %t6 = icmp eq i32 %t0, %t5
+  br i1 %t6, label %L4, label %L5
+
+; CHECK: [[LABEL2]]:
+; CHECK-NEXT: call void @goo()
+L4:
+  call void @goo()
+  ret void
+
+L5:
+  call void @hoo()
+  ret void
+}
Index: test/Other/pr32085.ll
===================================================================
--- test/Other/pr32085.ll
+++ test/Other/pr32085.ll
@@ -1,6 +1,7 @@
 ; RUN: opt -S -O1 < %s -o %t1.ll
 ;; Show that there's no difference after running another simplify CFG
-; RUN: opt -S -simplifycfg < %t1.ll -o %t2.ll
+; RUN: opt -S -simplifycfg < %t1.ll -o %t2.ll 
+; RUN: sed -i 's/; preds = .*//g' %t1.ll %t2.ll
 ; RUN: diff %t1.ll %t2.ll
 
 ; Test from LoopSink pass, leaves some single-entry single-exit basic blocks.
Index: lib/Transforms/Scalar/JumpThreading.cpp
===================================================================
--- lib/Transforms/Scalar/JumpThreading.cpp
+++ lib/Transforms/Scalar/JumpThreading.cpp
@@ -752,6 +752,8 @@
     CmpInst::Predicate Pred = Cmp->getPredicate();
 
     PHINode *PN = dyn_cast<PHINode>(CmpLHS);
+    if (!PN)
+      PN = dyn_cast<PHINode>(CmpRHS);
     if (PN && PN->getParent() == BB) {
       const DataLayout &DL = PN->getModule()->getDataLayout();
       // We can do this simplification if any comparisons fold to true or false.
@@ -762,14 +764,24 @@
         LVI->enableDT();
       for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
         BasicBlock *PredBB = PN->getIncomingBlock(i);
-        Value *LHS = PN->getIncomingValue(i);
-        Value *RHS = CmpRHS->DoPHITranslation(BB, PredBB);
-
+        Value *LHS, *RHS;
+        if (PN == CmpLHS) {
+          LHS = PN->getIncomingValue(i);
+          RHS = CmpRHS->DoPHITranslation(BB, PredBB);
+        } else {
+          LHS = CmpLHS->DoPHITranslation(BB, PredBB);
+          RHS = PN->getIncomingValue(i);
+        }
         Value *Res = SimplifyCmpInst(Pred, LHS, RHS, {DL});
         if (!Res) {
           if (!isa<Constant>(RHS))
             continue;
 
+          // getPredicateOnEdge call will make no sense if LHS is defined in BB.
+          auto LHSInst = dyn_cast<Instruction>(LHS);
+          if (LHSInst && LHSInst->getParent() == BB)
+            continue;
+
           LazyValueInfo::Tristate
             ResT = LVI->getPredicateOnEdge(Pred, LHS,
                                            cast<Constant>(RHS), PredBB, BB,


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D46275.144648.patch
Type: text/x-patch
Size: 3302 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20180430/7f742290/attachment.bin>