From 97fd9a58de3c99a74b0890a908430fa3ab894bed Mon Sep 17 00:00:00 2001 From: Dale Johannesen Date: Mon, 10 Jan 2011 21:53:07 +0000 Subject: [PATCH] Fix PR 8916 (qv for analysis), at least the immediate problem. There's an inherent tension in DAGCombine between assuming that things will be put in canonical form, and the Depth mechanism that disables transformations when recursion gets too deep. It would not surprise me if there's a lot of little bugs like this one waiting to be discovered. The mechanism seems fragile and I'd suggest looking at it from a design viewpoint. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123191 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/CodeGen/SelectionDAG/TargetLowering.cpp | 3 ++- test/CodeGen/X86/2011-01-10-DagCombineHang.ll | 15 +++++++++++++++ 2 files changed, 17 insertions(+), 1 deletion(-) create mode 100644 test/CodeGen/X86/2011-01-10-DagCombineHang.ll diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp index 396ebc15c6d..f9e0992ea14 100644 --- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp +++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp @@ -1176,8 +1176,9 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op, // the RHS. if (ConstantSDNode *RHSC = dyn_cast(Op.getOperand(1))) { APInt LHSZero, LHSOne; + // Do not increment Depth here; that can cause an infinite loop. TLO.DAG.ComputeMaskedBits(Op.getOperand(0), NewMask, - LHSZero, LHSOne, Depth+1); + LHSZero, LHSOne, Depth); // If the LHS already has zeros where RHSC does, this and is dead. if ((LHSZero & NewMask) == (~RHSC->getAPIntValue() & NewMask)) return TLO.CombineTo(Op, Op.getOperand(0)); diff --git a/test/CodeGen/X86/2011-01-10-DagCombineHang.ll b/test/CodeGen/X86/2011-01-10-DagCombineHang.ll new file mode 100644 index 00000000000..bf438b82edf --- /dev/null +++ b/test/CodeGen/X86/2011-01-10-DagCombineHang.ll @@ -0,0 +1,15 @@ +; RUN: llc < %s -mtriple=x86_64-apple-darwin10 +; This formerly got DagCombine into a loop, PR 8916. + +define i32 @foo(i64 %x, i64 %y, i64 %z, i32 %a, i32 %b) { +entry: + %"alloca point" = bitcast i32 0 to i32 ; [#uses=0] + %t1 = shl i64 %x, 15 + %t2 = and i64 %t1, 4294934528 + %t3 = or i64 %t2, %y + %t4 = xor i64 %z, %t3 + %t5 = trunc i64 %t4 to i32 + %t6 = add i32 %a, %t5 + %t7 = add i32 %t6, %b + ret i32 %t7 +}