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teach ComputeNumSignBits to look through PHI nodes.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92964 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-01-07 23:44:37 +00:00
parent e3874deb61
commit 8d10f9d4a8
3 changed files with 37 additions and 7 deletions
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23
lib/Analysis/ValueTracking.cpp
View File

@ -726,8 +726,7 @@ unsigned llvm::ComputeNumSignBits(Value *V, const TargetData *TD,
Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
if (Tmp2 == 1) return 1;
return std::min(Tmp, Tmp2)-1;
break;
return std::min(Tmp, Tmp2)-1;
case Instruction::Sub:
Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
@ -757,8 +756,24 @@ unsigned llvm::ComputeNumSignBits(Value *V, const TargetData *TD,
// is, at worst, one more bit than the inputs.
Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
if (Tmp == 1) return 1; // Early out.
return std::min(Tmp, Tmp2)-1;
break;
return std::min(Tmp, Tmp2)-1;
case Instruction::PHI: {
PHINode *PN = cast<PHINode>(U);
// Don't analyze large in-degree PHIs.
if (PN->getNumIncomingValues() > 4) break;
// Take the minimum of all incoming values. This can't infinitely loop
// because of our depth threshold.
Tmp = ComputeNumSignBits(PN->getIncomingValue(0), TD, Depth+1);
for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
if (Tmp == 1) return Tmp;
Tmp = std::min(Tmp,
ComputeNumSignBits(PN->getIncomingValue(1), TD, Depth+1));
}
return Tmp;
}
case Instruction::Trunc:
// FIXME: it's tricky to do anything useful for this, but it is an important
// case for targets like X86.

3
lib/Transforms/InstCombine/InstructionCombining.cpp
View File

@ -1027,8 +1027,6 @@ static bool AddReachableCodeToWorklist(BasicBlock *BB,
continue;
}
if (TD) {
// See if we can constant fold its operands.
for (User::op_iterator i = Inst->op_begin(), e = Inst->op_end();
@ -1048,7 +1046,6 @@ static bool AddReachableCodeToWorklist(BasicBlock *BB,
}
}
InstrsForInstCombineWorklist.push_back(Inst);
}

18
test/Transforms/InstCombine/shift-sra.ll
View File

@ -19,3 +19,21 @@ define i32 @test2(i8 %tmp) {
; CHECK: @test2
; CHECK: lshr i32 %tmp4, 3
}
define i64 @test3(i1 %X, i64 %Y, i1 %Cond) {
br i1 %Cond, label %T, label %F
T:
%X2 = sext i1 %X to i64
br label %C
F:
%Y2 = ashr i64 %Y, 63
br label %C
C:
%P = phi i64 [%X2, %T], [%Y2, %F]
%S = ashr i64 %P, 12
ret i64 %S
; CHECK: @test3
; CHECK: %P = phi i64
; CHECK-NEXT: ret i64 %P
}