Revert "SROA: Enhance speculateSelectInstLoads"

This reverts commit ffc3fb6.

Author: cdevadas

llvm/lib/Transforms/Scalar/SROA.cpp

@@ -1330,21 +1330,14 @@ static void speculatePHINodeLoads(PHINode &PN) {
 ///   %V = select i1 %cond, i32 %V1, i32 %V2
 ///
 /// We can do this to a select if its only uses are loads and if the operand
-/// to the select can be loaded unconditionally. If found an intervening bitcast
-/// with a single use of the load, allow the promotion.
+/// to the select can be loaded unconditionally.
 static bool isSafeSelectToSpeculate(SelectInst &SI) {
   Value *TValue = SI.getTrueValue();
   Value *FValue = SI.getFalseValue();
   const DataLayout &DL = SI.getModule()->getDataLayout();
 
   for (User *U : SI.users()) {
-    LoadInst *LI;
-    BitCastInst *BC = dyn_cast<BitCastInst>(U);
-    if (BC && BC->hasOneUse())
-      LI = dyn_cast<LoadInst>(*BC->user_begin());
-    else
-      LI = dyn_cast<LoadInst>(U);
-
+    LoadInst *LI = dyn_cast<LoadInst>(U);
     if (!LI || !LI->isSimple())
       return false;
 
@@ -1370,24 +1363,10 @@ static void speculateSelectInstLoads(SelectInst &SI) {
   Value *FV = SI.getFalseValue();
   // Replace the loads of the select with a select of two loads.
   while (!SI.use_empty()) {
-    LoadInst *LI;
-    BitCastInst *BC = dyn_cast<BitCastInst>(SI.user_back());
-    if (BC) {
-      assert(BC->hasOneUse() && "Bitcast should have a single use.");
-      LI = cast<LoadInst>(BC->user_back());
-    } else {
-      LI = cast<LoadInst>(SI.user_back());
-    }
-
+    LoadInst *LI = cast<LoadInst>(SI.user_back());
     assert(LI->isSimple() && "We only speculate simple loads");
 
     IRB.SetInsertPoint(LI);
-    if (BC) {
-      // Cast the operands to bitcast's target type.
-      TV = IRB.CreateBitCast(TV, BC->getType(), TV->getName() + ".sroa.cast");
-      FV = IRB.CreateBitCast(FV, BC->getType(), FV->getName() + ".sroa.cast");
-    }
-
     LoadInst *TL = IRB.CreateLoad(LI->getType(), TV,
                                   LI->getName() + ".sroa.speculate.load.true");
     LoadInst *FL = IRB.CreateLoad(LI->getType(), FV,
@@ -1411,8 +1390,6 @@ static void speculateSelectInstLoads(SelectInst &SI) {
     LLVM_DEBUG(dbgs() << "          speculated to: " << *V << "\n");
     LI->replaceAllUsesWith(V);
     LI->eraseFromParent();
-    if (BC)
-      BC->eraseFromParent();
   }
   SI.eraseFromParent();
 }

llvm/test/Transforms/SROA/phi-and-select.ll

@@ -60,14 +60,23 @@ entry:
   ret i32 %result
 }
 
+; If bitcast isn't considered a safe phi/select use, the alloca
+; remains as an array.
+; FIXME: Why isn't this identical to test2?
 define float @test2_bitcast() {
 ; CHECK-LABEL: @test2_bitcast(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[COND:%.*]] = icmp sle i32 0, 1
-; CHECK-NEXT:    [[TMP0:%.*]] = bitcast i32 1 to float
-; CHECK-NEXT:    [[TMP1:%.*]] = bitcast i32 0 to float
-; CHECK-NEXT:    [[RESULT_SROA_SPECULATED:%.*]] = select i1 [[COND]], float [[TMP0]], float [[TMP1]]
-; CHECK-NEXT:    ret float [[RESULT_SROA_SPECULATED]]
+; CHECK-NEXT:    [[A_SROA_0:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[A_SROA_3:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    store i32 0, i32* [[A_SROA_0]], align 4
+; CHECK-NEXT:    store i32 1, i32* [[A_SROA_3]], align 4
+; CHECK-NEXT:    [[A_SROA_0_0_A_SROA_0_0_V0:%.*]] = load i32, i32* [[A_SROA_0]], align 4
+; CHECK-NEXT:    [[A_SROA_3_0_A_SROA_3_4_V1:%.*]] = load i32, i32* [[A_SROA_3]], align 4
+; CHECK-NEXT:    [[COND:%.*]] = icmp sle i32 [[A_SROA_0_0_A_SROA_0_0_V0]], [[A_SROA_3_0_A_SROA_3_4_V1]]
+; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[COND]], i32* [[A_SROA_3]], i32* [[A_SROA_0]]
+; CHECK-NEXT:    [[SELECT_BC:%.*]] = bitcast i32* [[SELECT]] to float*
+; CHECK-NEXT:    [[RESULT:%.*]] = load float, float* [[SELECT_BC]], align 4
+; CHECK-NEXT:    ret float [[RESULT]]
 ;
 entry:
   %a = alloca [2 x i32]