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use getPredicateOnEdge to fold comparisons through PHI nodes, 

which implements GCC PR18046.  This also gets us 360 more
jump threads on 176.gcc.

llvm-svn: 86953
This commit is contained in:
Chris Lattner 2009-11-12 05:24:05 +00:00
parent 22db4b5e0c
commit 5f6b8b2bcb
2 changed files with 43 additions and 1 deletions
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12
llvm/lib/Transforms/Scalar/JumpThreading.cpp
View File

@ -368,7 +368,17 @@ ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){
Value *RHS = Cmp->getOperand(1)->DoPHITranslation(BB, PredBB);
Value *Res = SimplifyCmpInst(Cmp->getPredicate(), LHS, RHS, TD);
if (Res == 0) continue;
if (Res == 0) {
if (!LVI || !isa<Constant>(RHS))
continue;
LazyValueInfo::Tristate
ResT = LVI->getPredicateOnEdge(Cmp->getPredicate(), LHS,
cast<Constant>(RHS), PredBB, BB);
if (ResT == LazyValueInfo::Unknown)
continue;
Res = ConstantInt::get(Type::getInt1Ty(LHS->getContext()), ResT);
}
if (isa<UndefValue>(Res))
Result.push_back(std::make_pair((ConstantInt*)0, PredBB));

32
llvm/test/Transforms/JumpThreading/basic.ll
View File

@ -349,6 +349,38 @@ BB4:
ret i32 4
}
;; Correlated value through boolean expression. GCC PR18046.
define void @test12(i32 %A) {
; CHECK: @test12
entry:
%cond = icmp eq i32 %A, 0
br i1 %cond, label %bb, label %bb1
; Should branch to the return block instead of through BB1.
; CHECK: entry:
; CHECK-NEXT: %cond = icmp eq i32 %A, 0
; CHECK-NEXT: br i1 %cond, label %bb1, label %return
bb:
%B = call i32 @test10f2()
br label %bb1
bb1:
%C = phi i32 [ %A, %entry ], [ %B, %bb ]
%cond4 = icmp eq i32 %C, 0
br i1 %cond4, label %bb2, label %return
; CHECK: bb1:
; CHECK-NEXT: %B = call i32 @test10f2()
; CHECK-NEXT: %cond4 = icmp eq i32 %B, 0
; CHECK-NEXT: br i1 %cond4, label %bb2, label %return
bb2:
%D = call i32 @test10f2()
ret void
return:
ret void
}
;;; Duplicate condition to avoid xor of cond.