Revert r173342 temporarily. It appears to cause a very late miscompile

of stage2 in a bootstrap. Still investigating....

llvm-svn: 173343

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -1369,8 +1369,7 @@ static bool SinkThenElseCodeToEnd(BranchInst *BI1) {
 /// \endcode
 ///
 /// \returns true if the conditional block is removed.
-static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
-                                   const TargetTransformInfo &TTI) {
+static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB) {
   // Be conservative for now. FP select instruction can often be expensive.
   Value *BrCond = BI->getCondition();
   if (isa<FCmpInst>(BrCond))
@@ -1399,22 +1398,15 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
 
     // Only speculatively execution a single instruction (not counting the
     // terminator) for now.
-    SpeculationCost += TTI.getUserCost(I);
-    if (SpeculationCost > TargetTransformInfo::TCC_Basic)
+    ++SpeculationCost;
+    if (SpeculationCost > 1)
       return false;
 
     // Don't hoist the instruction if it's unsafe or expensive.
     if (!isSafeToSpeculativelyExecute(I))
       return false;
-    // FIXME: This should really be a cost metric, but our cost model doesn't
-    // accurately model the expense of select.
-    if (isa<SelectInst>(I))
+    if (ComputeSpeculationCost(I) > PHINodeFoldingThreshold)
       return false;
-    // FIXME: The cost metric currently doesn't reason accurately about simple
-    // versus complex GEPs, take a conservative approach here.
-    if (GEPOperator *GEP = dyn_cast<GEPOperator>(I))
-      if (!GEP->hasAllConstantIndices())
-        return false;
 
     // Do not hoist the instruction if any of its operands are defined but not
     // used in this BB. The transformation will prevent the operand from
@@ -1457,10 +1449,9 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
     // Account for the cost of an unfolded ConstantExpr which could end up
     // getting expanded into Instructions.
     // FIXME: This doesn't account for how many operations are combined in the
-    // constant expression. The cost functions in TTI don't yet correctly model
-    // constant expression costs.
-    SpeculationCost += TargetTransformInfo::TCC_Basic;
-    if (SpeculationCost > TargetTransformInfo::TCC_Basic)
+    // constant expression.
+    ++SpeculationCost;
+    if (SpeculationCost > 1)
       return false;
   }
 
@@ -3877,7 +3868,7 @@ bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
       TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
       if (Succ0TI->getNumSuccessors() == 1 &&
           Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
-        if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0), TTI))
+        if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
           return SimplifyCFG(BB, TTI, TD) | true;
     }
   } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
@@ -3886,7 +3877,7 @@ bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
     TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
     if (Succ1TI->getNumSuccessors() == 1 &&
         Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
-      if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1), TTI))
+      if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
         return SimplifyCFG(BB, TTI, TD) | true;
   }
 

llvm/test/Transforms/SimplifyCFG/SpeculativeExec.ll

@@ -108,32 +108,3 @@ end:
 
   ret i8* %x10
 }
-
-define i16 @test5(i1* %dummy, i16 %a, i16 %b) {
-; Test that we speculate no-op instructions.
-; CHECK: @test5
-
-entry:
-  %cond1 = load volatile i1* %dummy
-  br i1 %cond1, label %if, label %end
-
-if:
-  %cond2 = load volatile i1* %dummy
-  %a.conv = sext i16 %a to i32
-  %b.conv = sext i16 %b to i32
-  %cmp = icmp ult i32 %a.conv, %b.conv
-  br i1 %cond2, label %then, label %end
-
-then:
-  %sub = sub i32 %a.conv, %b.conv
-  %sub.conv = trunc i32 %sub to i16
-  br label %end
-
-end:
-  %x = phi i16 [ %a, %entry ], [ %b, %if ], [ %sub.conv, %then ]
-; CHECK-NOT: phi
-; CHECK: select i1
-
-  ret i16 %x
-}
-