Commit 002da67d authored by Nikita Popov's avatar Nikita Popov
Browse files

[InstCombine] Require ImmConstant in shift of shift fold 

This fixes an infinite loop reported at:
https://github.com/llvm/llvm-project/commit/82f68a992b9f89036042d57a5f6345cb2925b2c1#commitcomment-132406739
parent a4196666

llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp

+1 −1
Original line number Diff line number Diff line
@@ -760,7 +760,7 @@ Instruction *InstCombinerImpl::FoldShiftByConstant(Value *Op0, Constant *C1, 
  // (C2 >> X) >> C1 --> (C2 >> C1) >> X

  Constant *C2;

  Value *X;

  if (match(Op0, m_BinOp(I.getOpcode(), m_Constant(C2), m_Value(X))))

  if (match(Op0, m_BinOp(I.getOpcode(), m_ImmConstant(C2), m_Value(X))))

    return BinaryOperator::Create(

        I.getOpcode(), Builder.CreateBinOp(I.getOpcode(), C2, C1), X);

llvm/test/Transforms/InstCombine/shift-shift.ll

+12 −0
Original line number Diff line number Diff line
@@ -732,3 +732,15 @@ define <2 x i8> @lshr_shl_demand5_nonuniform_vec_both(<2 x i8> %x) { 
  %r = and <2 x i8> %shl, <i8 -4, i8 -16>

  ret <2 x i8> %r

}



@g = external global i8, align 8



define i64 @ashr_ashr_constexpr() {

; CHECK-LABEL: @ashr_ashr_constexpr(

; CHECK-NEXT:    [[SHR2:%.*]] = ashr exact i64 ptrtoint (ptr @g to i64), 3

; CHECK-NEXT:    ret i64 [[SHR2]]

;

  %shr = ashr i64 ptrtoint (ptr @g to i64), 1

  %shr2 = ashr i64 %shr, 2

  ret i64 %shr2

}