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

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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
This commit is contained in:
Chandler Carruth 2013-01-24 12:05:17 +00:00
parent 681add7a63
commit 47d8f6dca5
2 changed files with 48 additions and 8 deletions
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14
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -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;
}

42
test/Transforms/SimplifyCFG/SpeculativeExec.ll
View File

@ -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
}