From 5cf06d10f8ebd736d5c4bbabd3d6f9e4b10c9291 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov@redhat.com>
Date: Wed, 2 Mar 2022 12:48:54 +0100
Subject: [PATCH] Revert "[InstCombine] Support switch in phi to cond fold"

This reverts commit 0817ce86b540f909eade6a8d7370e1b47e863a70.

Seeing some ppc64le stage2 failures, reverting to investigate.
---
 llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp | 47 ++++++++--------------
 .../Transforms/InstCombine/simple_phi_condition.ll | 13 +++---
 2 files changed, 24 insertions(+), 36 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
index 85efd3e..f1a9128 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
@@ -1261,6 +1261,9 @@ static Value *simplifyUsingControlFlow(InstCombiner &Self, PHINode &PN,
   //      ...      ...
   //       \       /
   //    phi [true] [false]
+  if (!PN.getType()->isIntegerTy(1))
+    return nullptr;
+
   // Make sure all inputs are constants.
   if (!all_of(PN.operands(), [](Value *V) { return isa<ConstantInt>(V); }))
     return nullptr;
@@ -1270,49 +1273,30 @@ static Value *simplifyUsingControlFlow(InstCombiner &Self, PHINode &PN,
   if (!DT.isReachableFromEntry(BB))
     return nullptr;
 
-  // Determine which value the condition of the idom has for which successor.
-  LLVMContext &Context = PN.getContext();
+  // Check that the immediate dominator has a conditional branch.
   auto *IDom = DT.getNode(BB)->getIDom()->getBlock();
-  Value *Cond;
-  SmallDenseMap<ConstantInt *, BasicBlock *, 8> SuccForValue;
-  if (auto *BI = dyn_cast<BranchInst>(IDom->getTerminator())) {
-    if (BI->isUnconditional())
-      return nullptr;
-
-    Cond = BI->getCondition();
-    SuccForValue[ConstantInt::getTrue(Context)] = BI->getSuccessor(0);
-    SuccForValue[ConstantInt::getFalse(Context)] = BI->getSuccessor(1);
-  } else if (auto *SI = dyn_cast<SwitchInst>(IDom->getTerminator())) {
-    Cond = SI->getCondition();
-    for (auto Case : SI->cases())
-      SuccForValue[Case.getCaseValue()] = Case.getCaseSuccessor();
-  } else {
-    return nullptr;
-  }
-
-  if (Cond->getType() != PN.getType())
+  auto *BI = dyn_cast<BranchInst>(IDom->getTerminator());
+  if (!BI || BI->isUnconditional())
     return nullptr;
 
   // Check that edges outgoing from the idom's terminators dominate respective
   // inputs of the Phi.
+  BasicBlockEdge TrueOutEdge(IDom, BI->getSuccessor(0));
+  BasicBlockEdge FalseOutEdge(IDom, BI->getSuccessor(1));
+
   Optional<bool> Invert;
   for (auto Pair : zip(PN.incoming_values(), PN.blocks())) {
     auto *Input = cast<ConstantInt>(std::get<0>(Pair));
     BasicBlock *Pred = std::get<1>(Pair);
-    auto IsCorrectInput = [&](ConstantInt *Input) {
-      // The input needs to be dominated by the corresponding edge of the idom.
-      auto It = SuccForValue.find(Input);
-      return It != SuccForValue.end() &&
-             DT.dominates(BasicBlockEdge(IDom, It->second),
-                          BasicBlockEdge(Pred, BB));
-    };
+    BasicBlockEdge Edge(Pred, BB);
 
+    // The input needs to be dominated by one of the edges of the idom.
     // Depending on the constant, the condition may need to be inverted.
     bool NeedsInvert;
-    if (IsCorrectInput(Input))
-      NeedsInvert = false;
-    else if (IsCorrectInput(cast<ConstantInt>(ConstantExpr::getNot(Input))))
-      NeedsInvert = true;
+    if (DT.dominates(TrueOutEdge, Edge))
+      NeedsInvert = Input->isZero();
+    else if (DT.dominates(FalseOutEdge, Edge))
+      NeedsInvert = Input->isOne();
     else
       return nullptr;
 
@@ -1323,6 +1307,7 @@ static Value *simplifyUsingControlFlow(InstCombiner &Self, PHINode &PN,
     Invert = NeedsInvert;
   }
 
+  auto *Cond = BI->getCondition();
   if (!*Invert)
     return Cond;
 
diff --git a/llvm/test/Transforms/InstCombine/simple_phi_condition.ll b/llvm/test/Transforms/InstCombine/simple_phi_condition.ll
index cfbd386..a247a2e 100644
--- a/llvm/test/Transforms/InstCombine/simple_phi_condition.ll
+++ b/llvm/test/Transforms/InstCombine/simple_phi_condition.ll
@@ -279,7 +279,8 @@ define i8 @test_switch(i8 %cond) {
 ; CHECK:       default:
 ; CHECK-NEXT:    ret i8 42
 ; CHECK:       merge:
-; CHECK-NEXT:    ret i8 [[COND]]
+; CHECK-NEXT:    [[RET:%.*]] = phi i8 [ 1, [[SW_1]] ], [ 7, [[SW_7]] ], [ 19, [[SW_19]] ]
+; CHECK-NEXT:    ret i8 [[RET]]
 ;
 entry:
   switch i8 %cond, label %default [
@@ -320,7 +321,8 @@ define i8 @test_switch_direct_edge(i8 %cond) {
 ; CHECK:       default:
 ; CHECK-NEXT:    ret i8 42
 ; CHECK:       merge:
-; CHECK-NEXT:    ret i8 [[COND]]
+; CHECK-NEXT:    [[RET:%.*]] = phi i8 [ 1, [[SW_1]] ], [ 7, [[SW_7]] ], [ 19, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    ret i8 [[RET]]
 ;
 entry:
   switch i8 %cond, label %default [
@@ -360,7 +362,8 @@ define i8 @test_switch_subset(i8 %cond) {
 ; CHECK:       default:
 ; CHECK-NEXT:    ret i8 42
 ; CHECK:       merge:
-; CHECK-NEXT:    ret i8 [[COND]]
+; CHECK-NEXT:    [[RET:%.*]] = phi i8 [ 1, [[SW_1]] ], [ 7, [[SW_7]] ]
+; CHECK-NEXT:    ret i8 [[RET]]
 ;
 entry:
   switch i8 %cond, label %default [
@@ -447,8 +450,8 @@ define i8 @test_switch_inverted(i8 %cond) {
 ; CHECK:       default:
 ; CHECK-NEXT:    ret i8 42
 ; CHECK:       merge:
-; CHECK-NEXT:    [[TMP0:%.*]] = xor i8 [[COND]], -1
-; CHECK-NEXT:    ret i8 [[TMP0]]
+; CHECK-NEXT:    [[RET:%.*]] = phi i8 [ -1, [[SW_0]] ], [ -2, [[SW_1]] ], [ -3, [[SW_2]] ]
+; CHECK-NEXT:    ret i8 [[RET]]
 ;
 entry:
   switch i8 %cond, label %default [
-- 
2.7.4