Address a large chunk of this FIXME by accumulating the cost for

unfolded constant expressions rather than checking each one
independently.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173341 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Utils/SimplifyCFG.cpp

@@ -1446,14 +1446,12 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB) {
     if (Operator::getOpcode(CE) == Instruction::Select)
       return false;
 
-    // An unfolded ConstantExpr could end up getting expanded into
-    // Instructions. Don't speculate this and another instruction at
-    // the same time.
-    // FIXME: This is strange because provided we haven't already hit the cost
-    // of 1, this code will speculate an arbitrary number of complex constant
-    // expression PHI nodes. Also, this doesn't account for how complex the
-    // constant expression is.
-    if (SpeculationCost > 0)
+    // 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.
+    ++SpeculationCost;
+    if (SpeculationCost > 1)
       return false;
   }
 

test/Transforms/SimplifyCFG/SpeculativeExec.ll

@@ -66,3 +66,45 @@ end:
 
   ret i8* %x
 }
+
+define i8* @test4(i1* %dummy, i8* %a, i8* %b) {
+; Test that we don't speculate an arbitrarily large number of unfolded constant
+; expressions.
+; CHECK: @test4
+
+entry:
+  %cond1 = load volatile i1* %dummy
+  br i1 %cond1, label %if, label %end
+
+if:
+  %cond2 = load volatile i1* %dummy
+  br i1 %cond2, label %then, label %end
+
+then:
+  br label %end
+
+end:
+  %x1 = phi i8* [ %a, %entry ], [ %b, %if ], [ inttoptr (i64 1 to i8*), %then ]
+  %x2 = phi i8* [ %a, %entry ], [ %b, %if ], [ inttoptr (i64 2 to i8*), %then ]
+  %x3 = phi i8* [ %a, %entry ], [ %b, %if ], [ inttoptr (i64 3 to i8*), %then ]
+  %x4 = phi i8* [ %a, %entry ], [ %b, %if ], [ inttoptr (i64 4 to i8*), %then ]
+  %x5 = phi i8* [ %a, %entry ], [ %b, %if ], [ inttoptr (i64 5 to i8*), %then ]
+  %x6 = phi i8* [ %a, %entry ], [ %b, %if ], [ inttoptr (i64 6 to i8*), %then ]
+  %x7 = phi i8* [ %a, %entry ], [ %b, %if ], [ inttoptr (i64 7 to i8*), %then ]
+  %x8 = phi i8* [ %a, %entry ], [ %b, %if ], [ inttoptr (i64 8 to i8*), %then ]
+  %x9 = phi i8* [ %a, %entry ], [ %b, %if ], [ inttoptr (i64 9 to i8*), %then ]
+  %x10 = phi i8* [ %a, %entry ], [ %b, %if ], [ inttoptr (i64 10 to i8*), %then ]
+; CHECK-NOT: select
+; CHECK: phi i8*
+; CHECK: phi i8*
+; CHECK: phi i8*
+; CHECK: phi i8*
+; CHECK: phi i8*
+; CHECK: phi i8*
+; CHECK: phi i8*
+; CHECK: phi i8*
+; CHECK: phi i8*
+; CHECK: phi i8*
+
+  ret i8* %x10
+}